Display types: Difference between revisions

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=Many-element=
=Few-element=
==Backlit flat-panel displays==
==Lighting==
 
===Nixie tubes===
[[Image:Nixie2.gif|thumb|right|]]
<!--
<!--
Nixie tubes were some of the earliest outputs of computers


We may call them LCD, but that was an early generation
They have been a inefficient solution since the transistor or so.
LCD and TFT and various other acronyms are all the same idea, with different refinements on how the pixels work exactly.


There are roughly two parts of such monitors you can care about: How the backlight works, and how the pixels work.
But they're still pretty.


[[Lightbulb_notes#Nixie_tubes]]
-->
<br style="clear:both">


But almost all of them come down to
* pixels will block light, or less so.
* put a bright lights behind those
: in practice, they are on the side, and there is some trickery to try to reflect that as uniformly as possible


===Eggcrate display===


There are a lot of acronyms pointing tou
<!--
: TN and IPS is more about the crystals (and you mostly care about that if you care about viewing angle),
An eggcrate display is a number of often-incandescent, often-smallish lighbulbs in a grid (often 5 by 7),
: TFT is more about the electronics, but the two aren't really separable,
named for the pattern of round cutouts
: and then there are a lot of experiments (with their own acronyms) that


https://en.wikipedia.org/wiki/TFT_LCD


TFT, UFB, TFD, STN
These were bright, and primarily used in gameshows, presumably because they would show up fine even in bright studio lighting.
Note that when showing $0123456789, not all bulbs positions are necessary.




-->
-->


===CCFL or LED backlight===
==Mechanical==
 
===Mechanical counter===
 
https://en.wikipedia.org/wiki/Mechanical_counter
 
 


===Split-flap===
[[Image:Split-flap diagram.png|thumb|right]]
<!--
<!--
Both refer to a global backlight.
It's only things like OLED and QLED that do without.


If you're over thirty or so, you'll have seen these at airports. There's a few remaining now, but only a few.


CCFLs, Cold-Cathode Fluorescnt Lamps, are a variant of [[fluorescent lighting]] that (surprise) runs a lot colder than some other designs.
They're somehow satisfying to many, and that rustling sound is actually nice feedback on when you may want to look at the board again.


CCFL backlights tend to pulse at 100+ Hz{{verify}}, though because they necessarily use phosphors, and those can easily made to be slow, it may be a ''relatively'' steady pulsing.


They are also high voltage devices.
They are entirely mechanical, and only need to be moderately precise -- well, assuming they only need ~36 or so characters.




LED backlights are often either
https://www.youtube.com/watch?v=UAQJJAQSg_g
* [[PWM]]'d at kHz speeds{{verify}},
* current-limited{{verify}}, which are both smoother.
 




-->
-->


https://nl.wikipedia.org/wiki/CCFL
https://en.wikipedia.org/wiki/Split-flap_display
<br style="clear:both"/>


==Self-lit==


===OLED===
{{stub}}


While OLED is also a thing in lighting, OLED ''usually'' comes up in the context of OLED displays.
===Vane display===


It is mainly contrasted with backlit displays (because it is hard to get those to block all light).
OLEDs being off just emit no light at all. So the blacks are blacker, you could go brighter at the same time,
There are some other technical details why they tend to look a little crisper.


Viewing angles are also better, ''roughly'' because the light source is closer to the surface.
===Flip-disc===


https://en.wikipedia.org/wiki/Flip-disc_display


OLED are organic LEDs, which in itself party just a practical production detail, and really just LEDs.
{{comment|(...though you can get fancy in the production process, e.g. pricy see-through displays are often OLED with substate trickery{{verify}})}}


===Other flipping types===


<!--


PMOLED versus AMOLED makes no difference to the light emission,
-->
just to the way we access them (Passive Matrix, Active Matrix).
AMOLED can can somwhat lower power, higher speed, and more options along that scale{{verify}},
all of which makes them interesting for mobile uses. It also scales better to larger monitors.


POLED (and confusingly, pOLED is a trademark) uses a polymer instead of the glass,
==LED segments==
so is less likely to break but has other potential issues


===7-segment and others===
{{stub}}
[[File:Segment displays.png|thumb|right|200px|7-segment,
9-segment display, 14-segment, and 16-segment display. If meant for numbers will be a dot next to each (also common in general), if meant for time there will be a colon in one position.]]


<!--


'''Confusion'''
These are really just separate lights that happen to be arranged in a useful shape.


Very typically LEDs (with a common cathode or anode), though similar ideas are sometimes implemented in other display types - notably the electromechanical one, and also sometimes VFD.


"Isn't LED screen the same as OLED?"


No.  
Even the simplest, 7-segment LED involves a bunch of connectors so are
Marketers will be happy if you confuse "we used a LED backlight instead of a CCFL" (which we've been doing for ''ages'')
* often driven multiplexed, so only one of them is on at a time.
with "one of those new hip crisp OLED thingies", while not technically lying,
* often done via a controller that handles that multiplexing for you<!--
so they may be fuzzy about what they mean with "LED display".
: which one depends on context, e.g. is it a BCD-style calculator, a microcontroller; what interface is more convenient for you
:: if you're the DIY type who bought a board, you may be looking at things like the MAX7219 or MAX7221, TM1637 or TM1638, HT16K33, 74HC595 (shift register), HT16K33 
-->


You'll know when you have an OLED monitor, because it will cost ten times as much - a thousand USD/EUR, more at TV sizes.
The cost-benefit for people without a bunch of disposable income isn't really there.


Seven segments are the minimal and classical case,
good enough to display numbers and so e.g. times, but not really for characters.


More-than-7-segment displays are preferred for that.


"I heard al phones use OLED now?"


Fancier, pricier ones do, yes.


Cheaper ones do not, because the display alone might cost on the order of a hundred bucks.{{verify}}
https://en.wikipedia.org/wiki/Seven-segment_display


==DIY==


===LCD character dislays===


Character displays are basically those with predefined (and occasionally rewritable) fonts.


-->


===QLED===
====Classical interface====
<!--
It's quantum, so it's buzzword compatible. How is it quantum? Who knows!


The more barebones interface is often a 16 pin line with a pinout like


It may surprise you that this is LCD-style, not OLED-style,
* Ground
but is brighter than most LCD style,


they're still working on details like decent contrast.
* Vcc


* Contrast
: usually there's a (trim)pot from Vcc, or a resistor if it's fixed


Quantum Dot LCD  https://en.wikipedia.org/wiki/Quantum_dot_display


* RS: Register Select (character or instruction)
: in instruction mode, it receives commands like 'clear display', 'move cursor',
: in character mode,


-->
* RW: Read/Write
: tied to ground is write, which is usually the only thing you do


==On image persistence / burn-in==
* ENable / clk (for writing)
<!--
CRTs continuously illuminating the same pixels would somewhat-literally cook their phosphors a little,
leading to fairly-literal image burn-in.


* 8 data lines, but you can do most things over 4 of them


Other displays will have similar effects, but it may not be ''literal'' burn in, so we're calling it image persistence or image retention now.


* backlight Vcc
* Backlight gnd


'''LCD and TFT''' have no ''literal'' burn-in, but the crystals may still settle into a preferred state.
: there is limited alleviation for this


'''Plasma''' still has burn-in.


'''OLED''' seems to as well, though it's subtler.
The minimal, write-only setup is:
* tie RW to ground
* connect RS, EN, D7, D6, D5, and D4 to digital outs




Liquid crystals (LCD, TFT, etc.) have an persisting-image effect because
====I2C and other====
of the behaviour of liquid crystals when held at the same state ''almost always''.
<!--
Basically the above wrapped in a controller you can address via I2C or SPI (and usually they then speak that older parallel interface)


You can roughly describe this as having a preferred state they won't easily relax out of -- but there are a few distinct causes, different sensitivity to this from different types of panels, and different potential fixes.
Sometimes these are entirely separate ones bolted onto the classical interface.


Also, last time I checked this wasn't ''thoroughly'' studied.




Unplugging power (/ turning it off) for hours (or days, or sometimes even seconds) may help, and may not.
For DIY, you may prefer these just because it's less wiring hassle.
 
-->


A screensaver with white, or strong moving colors, or noise, may help.
===Matrix displays===


There are TVs that do something like this, like jostling the entire image over time, doing a blink at startup and/or periodically, or scanning a single dot with black and white (you probably won't notice).


===(near-)monochrome===




https://en.wikipedia.org/wiki/Image_persistence
====SSD1306====


http://www.jscreenfix.com/
OLED, 128x64@4 colors{{vierfy}}


http://gribble.org/lcdfix/
https://cdn-shop.adafruit.com/datasheets/SSD1306.pdf


{{search|statictv screensaver}}
====SH1107====


-->
OLED,


==VFD==
https://datasheetspdf.com/pdf-file/1481276/SINOWEALTH/SH1107/1
<gallery mode="packed" style="float:right" heights="200px">
VFD.jpg|larger segments
VFD-dots.jpg|dot matrix VFD
</gallery>


[[Vacuum Fluorescent Display]]s are vacuum tubes applied in a specific way - see [[Lightbulb_notes#VFDs]] for more details.
===Small LCD/TFTs / OLEDs===
{{stub}}


<br style="clear:both"/>
Small as in order of an inch or two (because the controllers are designed for a limited resolution?{{verify}}).


=Few-element=
==Lighting==


===Nixie tubes===
{{zzz|Note that, like with monitors, marketers really don't mind if you confuse LED-backlit LCD with OLED,
[[Image:Nixie2.gif|thumb|right|]]
and some of the ebays and aliexpresses sellers of the world will happily 'accidentally'
call any small screen OLED if it means they sell more.
 
This is further made more confusing by the fact that there are
* few-color OLEDs (2 to 8 colors or so, great for high contrast but ''only'' high cotnrast),
* [[high color]] OLEDs (65K),
...so you sometimes need to dig into the tech specs to see the difference between high color LCD and high color OLED.
}}
 
<!--
<!--
Nixie tubes were some of the earliest outputs of computers
[[Image:OLED.jpg|thumb|300px|right|Monochrome OLED]]
[[Image:OLED.jpg|thumb|300px|right|High color OLED]]
[[Image:Not OLED.jpg|thumb|400px|right|Not OLED (clearly backlit)]]
-->


They have been a inefficient solution since the transistor or so.


But they're still pretty.
When all pixels are off they give zero light pollution (unlike most LCDs) which might be nice in the dark.
These seem to appear in smaller sizes than small LCDs, so are great as compact indicators.


[[Lightbulb_notes#Nixie_tubes]]
-->
<br style="clear:both">


'''Can it do video or not?'''


===Eggcrate display===
If it ''does'' speak e.g. MIPI it's basically just a monitor, probably capable of decent-speed updates, but also the things you ''can'' connect to will (on the scale of microcontroller to mini-PC) be moderately powerful, e.g. a raspberry.


<!--
But the list below don't connect PC video cables.
An eggcrate display is a number of often-incandescent, often-smallish lighbulbs in a grid (often 5 by 7),
named for the pattern of round cutouts


Still, they have their own controller, and can hold their pixel state one way or the other, but connect something more command-like - so you can update a moderate amount of pixels with via an interface that is much less speedy or complex.


These were bright, and primarily used in gameshows, presumably because they would show up fine even in bright studio lighting.
You might get reasonable results over SPI / I2C for a lot of e.g. basic interfaces and guages.
By the time you try to display video you have to think about your design more.
Note that when showing $0123456789, not all bulbs positions are necessary.


For a large part because amount of pixels to update times the rate of frames per second has to fit through the communication (...also the display's capabilities).
There is a semi-standard parallel interface that might make video-speed things feasible.
This interface is faster than the SPI/I2C option, though not always ''that'' much, depending on hardware details.


-->


==Mechanical==
Even if the specs of the screen can do it in theory, you also have to have the video ready to send.
If you're running it from an RP2040 or ESP32, don't expect to libav/ffmpeg.


===Mechanical counter===
Say, something like the {{imagesearch|tinycircuits tinytv|TinyTV}} runs a 216x135 65Kcolor display from a from a [[RP2040]].


https://en.wikipedia.org/wiki/Mechanical_counter
Also note that such hardware won't be doing decoding and rescaling arbitrary video files.
They will use specifically pre-converted video.




In your choices, also consider libraries.
Things like [https://github.com/Bodmer/TFT_eSPI TFT_eSPI] has a compatibility list you will care about.


===Split-flap===
[[Image:Split-flap diagram.png|thumb|right]]
<!--


If you're over thirty or so, you'll have seen these at airports. There's a few remaining now, but only a few.


They're somehow satisfying to many, and that rustling sound is actually nice feedback on when you may want to look at the board again.


====Interfaces====
{{stub}}


They are entirely mechanical, and only need to be moderately precise -- well, assuming they only need ~36 or so characters.
<!--
 
* 4-line SPI
* 3-line SPI ([[half duplex]], basically)
* I2C
* 6800-series parallel
* 8080-series parallel interface


https://www.youtube.com/watch?v=UAQJJAQSg_g


The last two are 8-bit parallel interfaces. ''In theory'' these can be multiples faster,
though notice that in some practice you are instead limited by the display's controller,
your own ability to speak out data that fast, and the difference may not even be twice
(and note that [[bit-banging]] that parallel may take a lot more CPU than dedicated SPI would).


-->
The numbers aren't about capability, they seem to purely references then Intel versus Motorola origins of their specs{{verify}})
They are apparently very similar - the main differences being the read/write and enable, and in some timing.
: If they support both, 8080 seems preferable, in part because some only support that?{{verify}}


https://en.wikipedia.org/wiki/Split-flap_display
<br style="clear:both"/>


There are others that aren't quite ''generic'' high speed moniutor interfaces yet,
but too fast for slower hardware (e.g. CSI, MDDI)


https://forum.arduino.cc/t/is-arduino-6800-series-or-8080-series/201241/2


===Vane display===
-->


====ST7735====


===Flip-disc===
LCD, 132x162@16bits RGB


https://en.wikipedia.org/wiki/Flip-disc_display
<!--
* SPI interface (or parallel)


* 396 source line (so 132*RGB) and 162 gate line
* display data RAM of 132 x 162 x 18 bits


===Other flipping types===
* 2.7~3.3V {{verify}}


<!--


-->
Boards that expose SPI will have roughly:
: GND: power supply
: VCC: 3.3V-5.0V


==LED segments==
: SCL: SPI clock line
: SDA: SPI data line


===7-segment and others===
: RES: reset
{{stub}}
[[File:Segment displays.png|thumb|right|200px|7-segment,
9-segment display, 14-segment, and 16-segment display. If meant for numbers will be a dot next to each (also common in general), if meant for time there will be a colon in one position.]]


: D/C: data/command selection
: CS: chip Selection interface


These are really just separate lights that happen to be arranged in a useful shape.
: BLK: backlight control (often can be left floating, presumably pulled up/down)


Very typically LEDs (with a common cathode or anode), though similar ideas are sometimes implemented in other display types - notably the electromechanical one, and also sometimes VFD.


Lua / NodeMCU:
* [https://nodemcu.readthedocs.io/en/release/modules/ucg/ ucg]
* [https://nodemcu.readthedocs.io/en/release/modules/u8g2/ u8g2]
* https://github.com/AoiSaya/FlashAir-SlibST7735


Even the simplest, 7-segment LED involves a bunch of connectors so are
* often driven multiplexed, so only one of them is on at a time.
* often done via a controller that handles that multiplexing for you<!--
: which one depends on context, e.g. is it a BCD-style calculator, a microcontroller; what interface is more convenient for you
:: if you're the DIY type who bought a board, you may be looking at things like the MAX7219 or MAX7221, TM1637 or TM1638, HT16K33, 74HC595 (shift register), HT16K33 
-->


Arduino libraries
* https://github.com/adafruit/Adafruit-ST7735-Library
* https://github.com/adafruit/Adafruit-GFX-Library


Seven segments are the minimal and classical case,  
These libraries may hardcode some of the pins (particularly the SPI ones),
good enough to display numbers and so e.g. times, but not really for characters.
and this will vary between libraries.


More-than-7-segment displays are preferred for that.




'''ucg notes'''


https://en.wikipedia.org/wiki/Seven-segment_display


=DIY=
Fonts that exist:    https://github.com/marcelstoer/nodemcu-custom-build/issues/22
fonts that you have:  for k,v in pairs(ucg) do print(k,v) end


===LCD character dislays===


Character displays are basically those with predefined (and occasionally rewritable) fonts.
http://blog.unixbigot.id.au/2016/09/using-st7735-lcd-screen-with-nodemcu.html


-->


====Classical interface====
====ST7789====


The more barebones interface is often a 16 pin line with a pinout like
LCD, 240x320@16bits RGB


* Ground
https://www.waveshare.com/w/upload/a/ae/ST7789_Datasheet.pdf


* Vcc
====SSD1331====


* Contrast
OLED, 96x 64, 16bits RGB
: usually there's a (trim)pot from Vcc, or a resistor if it's fixed


https://cdn-shop.adafruit.com/datasheets/SSD1331_1.2.pdf


* RS: Register Select (character or instruction)
: in instruction mode, it receives commands like 'clear display', 'move cursor',
: in character mode,


* RW: Read/Write
====SSD1309====
: tied to ground is write, which is usually the only thing you do


* ENable / clk (for writing)
OLED, 128 x 64, single color?


* 8 data lines, but you can do most things over 4 of them
https://www.hpinfotech.ro/SSD1309.pdf


====SSD1351====


* backlight Vcc
OLED, 65K color
* Backlight gnd


https://newhavendisplay.com/content/app_notes/SSD1351.pdf


 
====HX8352C====
The minimal, write-only setup is:
LCD
* tie RW to ground
* connect RS, EN, D7, D6, D5, and D4 to digital outs
 
 
====I2C and other====
<!--
<!--
Basically the above wrapped in a controller you can address via I2C or SPI (and usually they then speak that older parallel interface)  
240(RGB)x480, 16-bit
-->
https://www.ramtex.dk/display-controller-driver/rgb/hx8352.htm


Sometimes these are entirely separate ones bolted onto the classical interface.




====HX8357C====


For DIY, you may prefer these just because it's less wiring hassle.
====R61581====


<!--
240x320
-->
-->


===Matrix displays===
====ILI9163====
LCD, 162x132@16-bit RGB


http://www.hpinfotech.ro/ILI9163.pdf


===(near-)monochrome===
====ILI9341====


<!--
240RGBx320, 16-bit
-->
https://cdn-shop.adafruit.com/datasheets/ILI9341.pdf


====SSD1306====
====ILI9486====
LCD, 480x320@16-bit RGB


OLED, 128x64@4 colors{{vierfy}}
https://www.hpinfotech.ro/ILI9486.pdf


https://cdn-shop.adafruit.com/datasheets/SSD1306.pdf
====ILI9488====
LCD
<!--
320(RGB) x 480
-->


====SH1107====
https://www.hpinfotech.ro/ILI9488.pdf


OLED,  
====PCF8833====
LCD, 132×132 16-bit RGB


https://datasheetspdf.com/pdf-file/1481276/SINOWEALTH/SH1107/1
https://www.olimex.com/Products/Modules/LCD/MOD-LCD6610/resources/PCF8833.pdf


===Small LCD/TFTs / OLEDs===
====SEPS225====
{{stub}}
LCD


Small as in order of an inch or two (because the controllers are designed for a limited resolution?{{verify}}).
https://vfdclock.jimdofree.com/app/download/7279155568/SEPS225.pdf




{{zzz|Note that, like with monitors, marketers really don't mind if you confuse backlit LCD with OLED,
====RM68140====
and some of the ebays and aliexpresses sellers of the world will happily 'accidentally'
LCD
call any small screen OLED if it means they sell more.
 
This is further made more confusing by the fact that there are
* few-color OLEDs (2 to 8 colors or so, great for high contrast but ''only'' high cotnrast),
* [[high color]] OLEDs (65K),
...so you sometimes need to dig into the tech specs to see the difference between high color LCD and high color OLED.
}}
 
<!--
<!--
[[Image:OLED.jpg|thumb|300px|right|Monochrome OLED]]
320 RGB x 480
[[Image:OLED.jpg|thumb|300px|right|High color OLED]]
[[Image:Not OLED.jpg|thumb|400px|right|Not OLED (clearly backlit)]]
-->
-->


https://www.melt.com.ru/docs/RM68140_datasheet_V0.3_20120605.pdf
====GC9A01====


When all pixels are off they give zero light pollution (unlike most LCDs) which might be nice in the dark.
LCD, 65K colors, SPI
These seem to appear in smaller sizes than small LCDs, so are great as compact indicators.


Seem to often be used on round displays{{verify}}


'''Can it do video or not?'''
https://www.buydisplay.com/download/ic/GC9A01A.pdf


If it ''does'' speak e.g. MIPI it's basically just a monitor, probably capable of decent-speed updates, but also the things you ''can'' connect to will (on the scale of microcontroller to mini-PC) be moderately powerful, e.g. a raspberry.
[[Category:Computer‏‎]]
[[Category:Hardware]]


But the list below don't connect PC video cables.
===Epaper===


Still, they have their own controller, and can hold their pixel state one way or the other, but connect something more command-like - so you can update a moderate amount of pixels with via an interface that is much less speedy or complex.
====SSD1619====


You might get reasonable results over SPI / I2C for a lot of e.g. basic interfaces and guages.
https://cursedhardware.github.io/epd-driver-ic/SSD1619A.pdf
By the time you try to display video you have to think about your design more.


For a large part because amount of pixels to update times the rate of frames per second has to fit through the communication (...also the display's capabilities).
<!--
There is a semi-standard parallel interface that might make video-speed things feasible.
====UC8151====
This interface is faster than the SPI/I2C option, though not always ''that'' much, depending on hardware details.


https://www.orientdisplay.com/wp-content/uploads/2022/09/UC8151C.pdf


Even if the specs of the screen can do it in theory, you also have to have the video ready to send.
If you're running it from an RP2040 or ESP32, don't expect to libav/ffmpeg.


Say, something like the {{imagesearch|tinycircuits tinytv|TinyTV}} runs a 216x135 65Kcolor display from a from a [[RP2040]].
-->


Also note that such hardware won't be doing decoding and rescaling arbitrary video files.
=Many-element - TV and monitor notes (and a little film)=
They will use specifically pre-converted video.
==Backlit flat-panel displays==
<!--


We may call them LCD, but that was an early generation
LCD and TFT and various other acronyms are all the same idea, with different refinements on how the pixels work exactly.


In your choices, also consider libraries.
There are roughly two parts of such monitors you can care about: How the backlight works, and how the pixels work.
Things like [https://github.com/Bodmer/TFT_eSPI TFT_eSPI] has a compatibility list you will care about.




But almost all of them come down to
* pixels will block light, or less so.
* put a bright lights behind those
: in practice, they are on the side, and there is some trickery to try to reflect that as uniformly as possible




====Interfaces====
There are a lot of acronyms pointing tou
{{stub}}
: TN and IPS is more about the crystals (and you mostly care about that if you care about viewing angle),
: TFT is more about the electronics, but the two aren't really separable,
: and then there are a lot of experiments (with their own acronyms) that


<!--
https://en.wikipedia.org/wiki/TFT_LCD
* 4-line SPI
* 3-line SPI ([[half duplex]], basically)
* I2C
* 6800-series parallel
* 8080-series parallel interface


TFT, UFB, TFD, STN


The last two are 8-bit parallel interfaces. ''In theory'' these can be multiples faster,
though notice that in some practice you are instead limited by the display's controller,
your own ability to speak out data that fast, and the difference may not even be twice
(and note that [[bit-banging]] that parallel may take a lot more CPU than dedicated SPI would).


The numbers aren't about capability, they seem to purely references then Intel versus Motorola origins of their specs{{verify}})
-->
They are apparently very similar - the main differences being the read/write and enable, and in some timing.
: If they support both, 8080 seems preferable, in part because some only support that?{{verify}}


===CCFL or LED backlight===


There are others that aren't quite ''generic'' high speed moniutor interfaces yet,
<!--
but too fast for slower hardware (e.g. CSI, MDDI)
Both refer to a global backlight.  
It's only things like OLED and QLED that do without.


https://forum.arduino.cc/t/is-arduino-6800-series-or-8080-series/201241/2


-->
CCFLs, Cold-Cathode Fluorescnt Lamps, are a variant of [[fluorescent lighting]] that (surprise) runs a lot colder than some other designs.


====ST7735====
CCFL backlights tend to pulse at 100+ Hz{{verify}}, though because they necessarily use phosphors, and those can easily made to be slow, it may be a ''relatively'' steady pulsing.


LCD, 132x162@16bits RGB
They are also high voltage devices.


<!--
* SPI interface (or parallel)


* 396 source line (so 132*RGB) and 162 gate line
LED backlights are often either
* display data RAM of 132 x 162 x 18 bits
* [[PWM]]'d at kHz speeds{{verify}},
* current-limited{{verify}}, which are both smoother.


* 2.7~3.3V {{verify}}




Boards that expose SPI will have roughly:
-->
: GND: power supply
: VCC: 3.3V-5.0V


: SCL: SPI clock line
https://nl.wikipedia.org/wiki/CCFL
: SDA: SPI data line


: RES: reset
==Self-lit==


: D/C: data/command selection
===OLED===
: CS: chip Selection interface
{{stub}}


: BLK: backlight control (often can be left floating, presumably pulled up/down)
While OLED is also a thing in lighting, OLED ''usually'' comes up in the context of OLED displays.


It is mainly contrasted with backlit displays (because it is hard to get those to block all light).
OLEDs being off just emit no light at all. So the blacks are blacker, you could go brighter at the same time,
There are some other technical details why they tend to look a little crisper.


Lua / NodeMCU:
Viewing angles are also better, ''roughly'' because the light source is closer to the surface.
* [https://nodemcu.readthedocs.io/en/release/modules/ucg/ ucg]
* [https://nodemcu.readthedocs.io/en/release/modules/u8g2/ u8g2]
* https://github.com/AoiSaya/FlashAir-SlibST7735




Arduino libraries
OLED are organic LEDs, which in itself party just a practical production detail, and really just LEDs.
* https://github.com/adafruit/Adafruit-ST7735-Library
{{comment|(...though you can get fancy in the production process, e.g. pricy see-through displays are often OLED with substate trickery{{verify}})}}
* https://github.com/adafruit/Adafruit-GFX-Library


These libraries may hardcode some of the pins (particularly the SPI ones),
and this will vary between libraries.




PMOLED versus AMOLED makes no difference to the light emission,
just to the way we access them (Passive Matrix, Active Matrix).
AMOLED can can somwhat lower power, higher speed, and more options along that scale{{verify}},
all of which makes them interesting for mobile uses. It also scales better to larger monitors.


'''ucg notes'''
POLED (and confusingly, pOLED is a trademark) uses a polymer instead of the glass,
 
so is less likely to break but has other potential issues


Fonts that exist:    https://github.com/marcelstoer/nodemcu-custom-build/issues/22
fonts that you have:  for k,v in pairs(ucg) do print(k,v) end


<!--


http://blog.unixbigot.id.au/2016/09/using-st7735-lcd-screen-with-nodemcu.html
'''Confusion'''


-->


====ST7789====
"Isn't LED screen the same as OLED?"


LCD, 240x320@16bits RGB
No.
Marketers will be happy if you confuse "we used a LED backlight instead of a CCFL" (which we've been doing for ''ages'')
with "one of those new hip crisp OLED thingies", while not technically lying,
so they may be fuzzy about what they mean with "LED display".


https://www.waveshare.com/w/upload/a/ae/ST7789_Datasheet.pdf
You'll know when you have an OLED monitor, because it will cost ten times as much - a thousand USD/EUR, more at TV sizes.
The cost-benefit for people without a bunch of disposable income isn't really there.


====SSD1331====


OLED, 96x 64, 16bits RGB


https://cdn-shop.adafruit.com/datasheets/SSD1331_1.2.pdf
"I heard al phones use OLED now?"


Fancier, pricier ones do, yes.


====SSD1309====
Cheaper ones do not, because the display alone might cost on the order of a hundred bucks.{{verify}}


OLED, 128 x 64, single color?


https://www.hpinfotech.ro/SSD1309.pdf


====SSD1351====


OLED, 65K color
-->
 
===QLED===
<!--
It's quantum, so it's buzzword compatible. How is it quantum? Who knows!
 


https://newhavendisplay.com/content/app_notes/SSD1351.pdf
It may surprise you that this is LCD-style, not OLED-style,
but is brighter than most LCD style,


====HX8352C====
they're still working on details like decent contrast.
LCD
<!--
240(RGB)x480, 16-bit
-->
https://www.ramtex.dk/display-controller-driver/rgb/hx8352.htm




Quantum Dot LCD  https://en.wikipedia.org/wiki/Quantum_dot_display


====HX8357C====


====R61581====
-->


==On image persistence / burn-in==
<!--
<!--
240x320
CRTs continuously illuminating the same pixels would somewhat-literally cook their phosphors a little,
-->
leading to fairly-literal image burn-in.


====ILI9163====
LCD, 162x132@16-bit RGB


http://www.hpinfotech.ro/ILI9163.pdf
Other displays will have similar effects, but it may not be ''literal'' burn in, so we're calling it image persistence or image retention now.


====ILI9341====


<!--
'''LCD and TFT''' have no ''literal'' burn-in, but the crystals may still settle into a preferred state.
240RGBx320, 16-bit
: there is limited alleviation for this
-->
https://cdn-shop.adafruit.com/datasheets/ILI9341.pdf


====ILI9486====
'''Plasma''' still has burn-in.
LCD, 480x320@16-bit RGB


https://www.hpinfotech.ro/ILI9486.pdf
'''OLED''' seems to as well, though it's subtler.


====ILI9488====
LCD
<!--
320(RGB) x 480
-->


https://www.hpinfotech.ro/ILI9488.pdf
Liquid crystals (LCD, TFT, etc.) have an persisting-image effect because
of the behaviour of liquid crystals when held at the same state ''almost always''.  


====PCF8833====
You can roughly describe this as having a preferred state they won't easily relax out of -- but there are a few distinct causes, different sensitivity to this from different types of panels, and different potential fixes.
LCD, 132×132 16-bit RGB


https://www.olimex.com/Products/Modules/LCD/MOD-LCD6610/resources/PCF8833.pdf
Also, last time I checked this wasn't ''thoroughly'' studied.


====SEPS225====
LCD


https://vfdclock.jimdofree.com/app/download/7279155568/SEPS225.pdf
Unplugging power (/ turning it off) for hours (or days, or sometimes even seconds) may help, and may not.


A screensaver with white, or strong moving colors, or noise, may help.


====RM68140====
There are TVs that do something like this, like jostling the entire image over time, doing a blink at startup and/or periodically, or scanning a single dot with black and white (you probably won't notice).
LCD
<!--
320 RGB x 480
-->


https://www.melt.com.ru/docs/RM68140_datasheet_V0.3_20120605.pdf


====GC9A01 (round)====


LCD, 65K colors, SPI
https://en.wikipedia.org/wiki/Image_persistence


https://www.buydisplay.com/download/ic/GC9A01A.pdf
http://www.jscreenfix.com/


[[Category:Computer‏‎]]
http://gribble.org/lcdfix/
[[Category:Hardware]]


=TV and monitor notes=
{{search|statictv screensaver}}


==On reproduction==
-->


====Reproduction that flashes====
==VFD==
<gallery mode="packed" style="float:right" heights="200px">
VFD.jpg|larger segments
VFD-dots.jpg|dot matrix VFD
</gallery>


{{stub}}
[[Vacuum Fluorescent Display]]s are vacuum tubes applied in a specific way - see [[Lightbulb_notes#VFDs]] for more details.


'''Mechanical film projectors''' flash individual film frames while that film is being held entirely still, before advancing that film to the next (while no light is coming out) and repeating.
<br style="clear:both"/>


{{comment|(see e.g. [https://www.youtube.com/watch?v%3dCsounOrVR7Q this] and note that it moves so quickly that you see ''that'' the film is taken it happens so quickly that you don't even see it move.  Separately, if you slow playback you can also see that it flashes ''twice'' before it advances the film - we'll get to why)}}




This requires a shutter, i.e. not letting through any light a moderate part of the time (specifically while it's advancing the film).
<!--
We are counting on our eyes to sort of ignore that.
==Capabilities==


One significant design concept very relevant to this type of reproduction is the '''flicker fusion threshold'''[https://en.wikipedia.org/wiki/Flicker_fusion_threshold], the "frequency at which intermittent light stimulus appears to be steady light" to our eyes.
===Resolution===
A TFT screen has a number of pixels, and therefore a natural resolution. Lower resolutions (and sometimes higher ones) can be displayed, but are interpolated so will not bee as sharp. Most people use the natural resolution.  
This may also be important for gamers, who may not want to be forced to a higher resolution for crispness than their graphics card can handle in terms of speed.


Research shows that this varies somewhat with conditions, but in most conditions practical around showing people images, that's somewhere between 50Hz and 90Hz.
For:
* 17": 1280x1024 is usual (1280x768 for widescreen)
* 19": 1280x1024 (1440x900 for widescreen)
* 20": 1600x1200 (1680x1050 for widescreen)
* 21": are likely to be 1600x1200 (1920x1200 for widescreen)




Since people are sensitive to flicker, some more than than others, and this can lead to eyestain and headaches,  
Note that some screens are 4:3 (computer-style ratio), some 5:4 (tv ratio), some 16:9 or 16:10 (wide screen), but often not ''exactly'' that, pixelwise; many things opt for some multiple that is easier to handle digitally.
we aim towards the high end of that range - whenever that's not hard to do.


In fact, while film is 24fps and was initially shown at 24Hz flashes, movie projectors soon introduced two-blade and then three-blade shutters, showing each image two or three times before advancing, meaning that while they still only show 24 distinct images per second, they flash it twice or three times for a ''regular'' 48Hz or 72Hz flicker, for a lot less eyestrain.
===Refresh===
Refresh rates as they existed in CRT monitors do not directly apply; there is no line scanning going on anymore.




Pixels are continuously lit, which is why TFTs don't seem to flicker like CRTs do. Still, they react only so fast to the changes in the intensity they should display at, which limits the amount of pixel changes that you will actually see per second.


An arguably even more basic constraint to moving pictures is the point at which rate of images we accept animation as '''fluid movement'''.  
Longer refresh times mean moving images are blurred and you may see ghosting of brigt images. Older TFT/LCDs did something on the order of 20ms (roughly 50fps), which was is not really acceptable for gaming.
: Anything under 10fps looks jerky and stilted or at least like a ''choice'' (western and eastern animation were rarely higher than 12, or 8 or 6 for the simpler ones),
: around 20fps we start readily accepting it as continuous movement,
: above 30 or 40fps it looks smooth,
: and above that it keeps on looking a little better ''yet'' also becomes quickly diminishing returns.




Early movies on film were approximately 24fps, some faster, various slower.  
However, the millisecond measure is nontrivial. The direct meaning of the number has been slaughtered primarily by number-boast-happy PR departments.
The number 24 was a chosen balance between barious things, like the fact that that's enough for fluid movement and relatively few scenes need higher,
and the fact that film stock is expensive, and a standard for projection (adaptable or even multiple projectors would be too expensive for most cinemas).


More exactly, there are various things you can be measuring. It's a little like the speaker rating (watt RMS, watt 'in regular use', PMPO) in that a rating may refer unrealistic exhaggerations as well as strict and real measures.


The reason we ''still'' use 24fps it now is more varied and doesn't really have a one-sentence answer.


But part of it is that making movies go faster is only sometimes well received.  
The argument is that even when the time for a pixel to be fully off to fully on may take 20ms, not everyone is using their monitor to induce epileptic attacks - usually the pixel is done faster, going from some grey to some grey. If you play the DOOM3 dark-room-fest, you may well see the change from that dark green to that dark blue happen in 8ms (not that that's in any way easy to measure).
But a game with sharp contrasts may see slower, somewhat blurry changes.


It seems that we associated 24fps to feels like movies, 50/60fps feels like shaky-cam home movies made by dad's camcorder (when those were still a thing) or sports broadcasts (which we did even though it reduced detail) with their tense, immediate, real-world associations.
So higher, while technically better, was also associated with a specific aesthetic. It mat works well for action movies, yet less for others.


There is an argument that 24fps's sluggishness puts us more at ease, reminds us that it isn't real, seems associated with storytelling, a dreamlike state, memory recall.
8ms is fairly usual these days. Pricier screens will do 4ms or even 2ms, which is nicer for gaming.


Even if we can't put our finger on why, such senses persist.


<!--
===Video noise===




'''when more is and isn't better'''
===Contrast===
The difference between the weakest and strongest brightness it can display. 350:1 is somewhat minimal, 400:1 and 500:1 are fairly usual, 600:1 and 800:1 are nice and crisp.


And you can argue that cinematic language evolved not only with the technical limitations, but also the limitations of how much new information you can show at all.
===Brightness===
The amount of light emitted - basically the strength of the backlight. Not horribly interesting unless you like it to be bright in even a well lit room.


In some ways, 24fps feels a subtle slightly stylized type of video,
300 cd/m2 is fairly usual.
from the framerate alone,
and most directors will like this because most movies benefit from that.
Exceptions include some fast paced - but even they benefit from feeling more distinct from ''other'' movies still doing that stylized thing.




At the same time, a lot of seems like a learned association that will blur and may go away over time.
There are details like brightness uniformity - in some monitors, the edges are noticably darker when the screen is bright, which may be annoying. Some monitors have stranger shapes for their lighting.


Only reviews will reveal this.


Some changes will make things ''better'' (consider that the [[3-2 pulldown]] necessary to put 24fps movies on TV in 60Hz countries made pans look ''worse'').
===Color reproduction===
The range of colors a monitor can reproduce is interesting for photography buffs. The curve of how each color is reproduced is also a little different for every monitor, and for some may be noticeably different from others.  


This becomes relevant when you want a two-monitor deal; it may be hard to get a CRT and a TFT the same color, as much as it may be hard to get two different TFTs from the same manufacturer consistent. If you want perfection in that respect, get two of the same - though spending a while twiddlign with per-channel gamma correction will usually get decent results.


You can get away with even less in certain aesthetic styles - simpler cartoons may update at 8fps or 6fps, and we're conditioned enough that in that cartoon context, 12fps looks ''fancy''.  But more is generally taken to be worse. It may be objectively smoother but there are so many animation choices (comparable to cinematic language) that you basically ''have'' to throw out at high framerates - or accept that it will look ''really'' jarring when it switches between them. It ''cannot'' look like classical animation/anime, for better ''and'' worse.  And that's assuming it was ''made'' this way -- automatic resolution upscaling usually implies filters - they things, they are effectively a stylistic change that was not intended and you can barely control. Automatic frame interpolation generally does ''terribly'' on anime because it was trained on photographic images instead. The more stylistic the animation style, the worse it will look interpolated, never mind that it will deal poorly with intentional animation effects like [https://en.wikipedia.org/wiki/Squash_and_stretch stretch and squash] and in particular [https://en.wikipedia.org/wiki/Smear_frame smear frames].
-->


====CRT screens====
{{stub}}


==Convenience==


'''Also flashing'''
===Viewing angle===
The viewing angle is a slightly magical figure. It's probably well defined in a test, but its meaning is a little elusive.


CRT monitors do something ''vaguely'' similar to movie projectors, in that they light up an image so-many times a second.
Basically it indicates at which angle the discoloration starts being noticeable. Note that the brightness is almost immediately a little off, so no TFT is brilliant to show photos to all the room. The viewing angle is mostly interesting for those that have occasional over-the-shoulder watchers, or rather watchers from other chairs and such.


Where with film you spend a least some of the time with the entire image being lit up continuously (and some time with the shutter coming in and out).
The angle, either from a perpendicular line (e.g. 75°) or as a total angle (e.g. 150°).
with a CRT there is a constantly-flowing beam of electrons lighting whatever phosphor it hits,  
As noted, the figure is a little magical. If it says 178° the colors will be as good as they'll be from any angle, but frankly, for lone home use, even the smallest angle you can find tends to be perfectly fine.
and that beam that is being dragged line-by-line along the screen - look at [https://youtu.be/3BJU2drrtCM?t=137 slow motion footage like this].


The phosphor will have a softish onset and retain light for some while,
===Reflectivity===
and while slow motion tends to exaggerate that a little (looks like a single line),  
While there is no formal measure for this, you may want to look at getting something that isn't reflective. If you're in an office near a window, this is probably about as important to easily seeing your screen as its brightness is.
it's still visible for much less than 1/60th of a second.


The largest reason that these pulsing phosphors don't look like harsh blinking is that our persistence of vision
(you could say our eyes framerate sucks, though actually this is a poor name for our eyes's actual mechanics), combined with the fact that it's relatively bright.


It seems that many glare filters will reduce your color fidelity, though.


<!--
Analog TVs were almost always 50Hz or 60Hz (depending on country).
(separately, broadcast would often only show 25 or 30 new image frames, depending on the type of content content - read up on [[interlacing]] and [[three-two pull down]]).


Most CRT ''monitors'', unlike TVs, can be told to refresh at different rates.


There's a classical 60Hz mode that was easy to support, but people often preferred 72Hz or 75Hz or 85Hz or higher modes because they reduced eyestrain.
-->
==Some theory - on reproduction==


====Reproduction that flashes====


And yes, after working behind one of those faster-rate monitors and moving to a 60Hz monitor would be ''really'' noticeable.
{{stub}}
Because even when we accept it as smooth enough, it still blinked, and we still perceive it as such.


'''Mechanical film projectors''' flash individual film frames while that film is being held entirely still, before advancing that film to the next (while no light is coming out) and repeating.


'''How do pixels get sent?'''
(see e.g. [https://www.youtube.com/watch?v%3dCsounOrVR7Q this] and note that it moves so quickly that you see ''that'' the film is taken it happens so quickly that you don't even see it move.  Separately, if you slow playback you can also see that it flashes ''twice'' before it advances the film - we'll get to why)


This requires a shutter, i.e. not letting through ''any'' light a moderate part of the time (specifically while it's advancing the film).
We are counting on our eyes to sort of ignore that.




-->
One significant design concept very relevant to this type of reproduction is the [https://en.wikipedia.org/wiki/Flicker_fusion_threshold '''flicker fusion threshold'''], the "frequency at which intermittent light stimulus appears to be steady light" to our eyes because separately from actual image it's showing, it appearing smooth is, you know, nice.


====Flatscreens====
Research shows that this varies somewhat with conditions, but in most conditions practical around showing people images, that's somewhere between 50Hz and 90Hz.
{{stub}}


Film projectors and CRTs don't matter directly to the discussion of 'what rate do you need',
because the flatscreens that most of us use do not flicker like that {{comment|(except some do, and ''intentionally so'', but we'll put that aside)}}.


While in film, and in CRTs, the mechanism that lights it up and the mechanism that shows the image is the same mechanism, so inseparable,
Since people are sensitive to flicker to varying degrees, and this can lead to eyestain and headaches,  
in LCD-style flatscreens (including QLED) they are separate - there is a global CCFL or LED backlight, and the pixels are light ''blockers''.
we aim towards the high end of that range whenever that is not hard to do.
{{comment|(In QLED there are the same again, though with some new footnotes)}}


In fact, we did so even with film. While film is 24fps and was initially shown at 24Hz flashes, movie projectors soon introduced two-blade and then three-blade shutters, showing each image two or three times before advancing, meaning that while they still only show 24 distinct images per second, they flash it twice or three times for a ''regular'' 48Hz or 72Hz flicker.
No more detail, but a bunch less eyestrain.


And global backlights tend to be lit fairly continuously.
There is still variation in backlights, mind, and some will still give you a little more eye strain than others.


When a backlight is CCFL, its phosphors are intentionally be made to decay slowly so even if the panel is a mere 100Hz,
that CCFL would look much less blinky than e.g. CRT at 100Hz.


LED backlights are often [[PWM]]'d at kHz speeds{{verify}}, or current-limited{{verify}}, which are both smoother.
As to what is actually being show, an arguably even more basic constraint is the rate of new images that we accept as '''fluid movement'''.
If you take a high speed camera, you may still not see it flicker [https://youtu.be/3BJU2drrtCM?t=267 this part of the same slow motion video] {{comment|(note how the backlight appears constant even when the pixel update is crawling by)}} until you get really fast and specific.
: Anything under 10fps looks jerky and stilted
:: or at least like a ''choice''.
:: western ''and'' eastern animations were rarely higher than 12, or 8 or 6 for the simpler/cheaper ones
: around 20fps we start readily accepting it as continuous movement,  
: above 30 or 40fps it looks smooth,
: and above that it keeps on looking a little better yet, with quickly diminishing returns




So the difference between, say, a 60fps and 240fps monitor isn't in the lighting, it's how fast the light-blocking pixels in front of that constant backlight change.
A 60fps monitor changes its pixels every 16ms (1/60 sec), a 240fps the latter every 4ms (1/240 sec).




A CRT at 30Hz would look very blinky and be hard on the eyes. A flatscreen at 30fps updates looks choppy but the lighting would be constant.
'''So why 24?'''


So in one way, it's more about the fps, but at the same time, the Hz rating usually ''is'' its physical fps.
Film's 24 was not universal at the time, and has no strong significance then or now.
It's just that when a standard was needed, the number 24 was a chosen balance between various aspects, like the fact that that's enough for fluid movement and relatively few scenes need higher, and the fact that film stock is expensive, and a standard for projection (adaptable or even multiple projectors would be too expensive for most cinemas).


<!--
'''Footnotes to backlight'''


Note also that dimming a PWM'd backlight screen will effectively change the flicker a little.
The reason we ''still'' use 24fps ''today'' is more faceted, and doesn't really have a one-sentence answer.
At high speeds this should not matter perceptibly, though.  


On regular screens the dimming is usually fixed, for laptop screens it may do so based on battery status as well as ambient light.
But part of it is that making movies go faster is not always well received.  


There are another few reasons why both can flicker a little more than that suggests, but only mildly so.
It seems that we associated 24fps to feels like movies, 50/60fps feels like shaky-cam home movies made by dad's camcorder (when those were still a thing) or sports broadcasts (which we did even though it reduced detail) with their tense, immediate, real-world associations.
So higher, while technically better, was also associated with a specific aesthetic. It mat works well for action movies, yet less for others.


There is an argument that 24fps's sluggishness puts us more at ease, reminds us that it isn't real, seems associated with storytelling, a dreamlike state, memory recall.


Even if we can't put our finger on why, such senses persist.


People who are more sensitive to eyestrain and related headaches will want to know the details of the backlight, because the slowest LED PWM will still annoy you, and you're looking for faster PWM or current-limited.
<!--
'''when more both is and isn't better'''


But it's often not specced very well - so whether any particular monitor is better or worse for eyestrain is essentially not specced.
And you can argue that cinematic language evolved not only with the technical limitations, but also the limitations of how much new information you can show at all.


In some ways, 24fps feels a subtle slightly stylized type of video,
from the framerate alone,
and most directors will like this because most movies benefit from that.
Exceptions include some fast paced - but even they benefit from feeling more distinct from ''other'' movies still doing that stylized thing.


-->


At the same time, a lot of seems like a learned association that will blur and may go away over time.


=====On updating pixels=====


<!--
Some changes will make things ''better'' (consider that the [[3-2 pulldown]] necessary to put 24fps movies on TV in 60Hz countries made pans look ''worse'').


To recap, '''in TVs and CRT monitors''', there is a narrow stream of electrons steered across the screen, making small bits of phosphor glow, one line at a time {{comment|(the line nature is not the only way to use a CRT, see e.g. [https://en.wikipedia.org/wiki/Vector_monitor vector monitors], and CRT oscilloscopes are also interesting, but it's a good way to do a generic display)}}


So yes, a TV and CRT monitor is essentially updated one pixel at a time, which happens so fast you would need a ''very'' fast camera
You can get away with even less in certain aesthetic styles - simpler cartoons may update at 8fps or 6fps, and we're conditioned enough that in that cartoon context, 12fps looks ''fancy''.  But more is generally taken to be worse. It may be objectively smoother but there are so many animation choices (comparable to cinematic language) that you basically ''have'' to throw out at high framerates - or accept that it will look ''really'' jarring when it switches between them. It ''cannot'' look like classical animation/anime, for better ''and'' worse.  And that's assuming it was ''made'' this way -- automatic resolution upscaling usually implies filters - they things, they are effectively a stylistic change that was not intended and you can barely control. Automatic frame interpolation generally does ''terribly'' on anime because it was trained on photographic images instead. The more stylistic the animation style, the worse it will look interpolated, never mind that it will deal poorly with intentional animation effects like [https://en.wikipedia.org/wiki/Squash_and_stretch stretch and squash] and in particular [https://en.wikipedia.org/wiki/Smear_frame smear frames].
to notice this - see e.g. [https://youtu.be/3BJU2drrtCM?t=52].
-->


This means that there needs to be something that controls the left-to-right and top-to-bottom steering[https://youtu.be/l4UgZBs7ZGo?t=307] - and because you're really just bending it back and forth, there are also times at which that bending shouldn't be visible, which is solved by just not emitting electrons, called the blanking intervals. If you didn't have horizontal blanking interval between lines, you would see nearly-horizontal lines as it gets dragged back for the next line; if you didn't have vertical blanking interval between frames you would see a diagonal line while it gets dragged back to the start of the next frame.
====CRT screens====
{{stub}}


In CRTs monitors, '''hsync''' and '''vsync''' names signals that (not control it directly but) help that movement happen.


'''Also flashing'''


CRTs were driven relatively directly from the graphics card, in the sense that the values of the pixel we're beaming onto a pixel will be the value that is on the line ''at that very moment''.
CRT monitors do something ''vaguely'' similar to movie projectors, in that they light up an image so-many times a second.
It would be hard and expensive to do any buffering, and there would be no reason (the phosphor's short term persistance is a buffer of sorts).  


So there needs to be a precisely timed stream of pixel data that is passed to the phosphors,
and you spend most of the interval drawing pixels (all minus the blanking parts).}}


Where with film you light up the entire thing at once {{comment|(maybe with some time with the shutter coming in and out, ignore that for now)}}.
a CRT light up one spot at a time - there is a beam constantly being dragged line by line across the screen -- look at [https://youtu.be/3BJU2drrtCM?t=137 slow motion footage like this].


The phosphor will have a softish onset and retain light for some while,
and while slow motion tends to exaggerate that a little (looks like a single line),
it's still visible for much less than 1/60th of a second.


'''How are CRT monitors different from CRT TVs?'''
The largest reason that these pulsing phosphors don't look like harsh blinking is that our persistence of vision
(you could say our eyes framerate sucks, though actually this is a poor name for our eyes's actual mechanics), combined with the fact that it's relatively bright.


In TVs, redraw speeds were basically set in stone, as were some decoding details.
It was still synchronized from the signal, but the speed was basically fixed, as that made things easier.


On color TV there were some extra details, but a good deal worked the same way.
<!--
Analog TVs were almost always 50Hz or 60Hz (depending on country).
(separately, broadcast would often only show 25 or 30 new image frames, depending on the type of content content - read up on [[interlacing]] and [[three-two pull down]]).


Early game consoles/computers just generated a TV signal, so that you could use the TV you already had.
Most CRT ''monitors'', unlike TVs, can be told to refresh at different rates.


After that, CRT monitors started out as adapted CRT TVs.
There's a classical 60Hz mode that was easy to support, but people often preferred 72Hz or 75Hz or 85Hz or higher modes because they reduced eyestrain.
Yet we were not tied to the broadcast format,
so it didn't take long at all before speed at which things are drawn was configurable.
By the nineties it wasn't too unusual to drive a CRT monitor at 56, 60, 72, 75, perhaps 85, and sometimes 90{{verify}}, 100, or 120Hz.


We also grew an increasing amount of resolutions that the monitor should be capable of displaying.
Or rather, resolution-refresh combinations. Detecting and dealing that is a topic in and of itself.


And yes, after working behind one of those faster-rate monitors and moving to a 60Hz monitor would be ''really'' noticeable.
Because even when we accept it as smooth enough, it still blinked, and we still perceive it as such.


Yet at the CRT level, they were driven much the same way -
synchronization timing to let the monitor know when and how fast to sweep the beams around,
and a stream of pixels passed through as they arrive on the wires.


So a bunch of the TV mechanism lived on into CRT monitors - and even into the flatscreen era.
'''How do pixels get sent?'''


That means that at, say, 60fps, roughly 16.6 milliseconds per frame,
''most'' of that 16ms is spent moving values onto the wire and onto the screen.




-->


====Flatscreens====
{{stub}}


'''How are flatscreens different from CRTs?'''
Flatscreens do not reproduce by blinking things at us.


The physical means of display is completely different.
While in film, and in CRTs, the mechanism that lights up the screen is the is the same mechanism as the one that shows you the image,
in LCD-style flatscreens, the image updates and the lighting are now different mechanisms.


There is a constant backlight, and from the point of view of a single LCD pixel,
Basically, there's one overall light behind the pixely part of the screen, and each screen pixel blocks light.  
the crystal's blocking-or-not state will sit around until asked to change.




And yet the sending-pixels part is still much the same.
That global backlights tends to be lit ''fairly'' continuously.
Consider that a ''single'' frame is millions of numbers (e.g. 1920 * 1080 * 3 colors ~= 6 million).
Sure there is variation in backlights, and some will still give you a little more eye strain than others.
For PCs with color this was never much under a million.


Regardless of how many colors,  
CCFL backlight phosphors seem intentionally made to decay slowly,
actually just transferring that many individual values will take some time.
so even if the panel is a mere 100Hz, that CCFL ''ought'' to look look much less blinky than e.g. CRT at 100Hz.




The hsync and vsync signals still exist,
LED backlights are often [[PWM]]'d at kHz speeds{{verify}}, or current-limited{{verify}}, which are both smoother.
though LCDs are often a little more forgiving, apparently keeping a short memory and allowing some syncing [https://youtu.be/muuhgrige5Q?t=425]
 
If you take a high speed camera, you may still not see it flicker [https://youtu.be/3BJU2drrtCM?t=267 this part of the same slow motion video] {{comment|(note how the backlight appears constant even when the pixel update is crawling by)}} until you get really fast and specific.




So the difference between, say, a 60fps and 240fps monitor isn't in the lighting, it's how fast the light-blocking pixels in front of that constant backlight change. 
A 60fps monitor changes its pixels every 16ms (1/60 sec), a 240fps the latter every 4ms (1/240 sec). The light just stays on.


Does a monitor have a framebuffer and then update everything at once?
As such, while a cRT at 30Hz would look very blinky and be hard on the eyes,
It ''could'' be designed that way if there was a point, but there rarely is.
a flatscreen at 30fps updates looks choppy but not like a blinky eyestrain.
It would only make things more expensive for no reason.




When the only thing we are required to do is to finish drawing one image before the next starts,
<!--
then we can spend most of that time sending pixels,
'''Footnotes to backlight'''
and the screen, while it has more flexibility in ''how'' exactly, can spend most of the refresh interval updating pixels.
...basically as in the CRT days.


Note also that dimming a PWM'd backlight screen will effectively change the flicker a little.
At high speeds this should not matter perceptibly, though. 


And when we were using VGA on flatscreens, that was what we were doing.
On regular screens the dimming is usually fixed, for laptop screens it may do so based on battery status as well as ambient light.


Panels even tend to update a line at a time.  
There are another few reasons why both can flicker a little more than that suggests, but only mildly so.


Why?
: the ability to update specific pixels would require a lot more wiring - a per-line addressing is already a good amount of wires (there is a similar tradeoff in camera image sensor readout, but in the other direction)
: LCDs need to be refreshed somewhat like DRAM (LCD doesn't like being held at a constant voltage, so monitors apply the pixel voltage in alternating polarities each frame. (This is not something you really need to worry about. [http://www.techmind.org/lcd/index.html#inversion It needs an ''extremely'' specifc image to see])).




People who are more sensitive to eyestrain and related headaches will want to know the details of the backlight, because the slowest LED PWM will still annoy you, and you're looking for faster PWM or current-limited.


Scanout itself basically refers to the readout and transfer of the framebuffer on the PC side,
But it's often not specced very well - so whether any particular monitor is better or worse for eyestrain is essentially not specced.


'''Scanout lag''' can refer to
: the per-line update
: the lag in pixel change, GtG stuff
:


-->


You can find some high speed footage of a monitor updating, e.g. [https://blurbusters.com/understanding-display-scanout-lag-with-high-speed-video here]
which illustrates terms like [[GtG]] (and why they both are and are not a sales trick):
Even if a lines's values are updated in well under a millisecond, the pixels may need ~5ms to settle on their new color,
and seen at high speeds, this looks like a range of the screen is a blur between the old and new image.


=====On updating pixels=====


<!--


'''Would it be technically possible to update all this-many million pixels at the same time? '''
To recap, '''in TVs and CRT monitors''', there is a narrow stream of electrons steered across the screen, making small bits of phosphor glow, one line at a time {{comment|(the line nature is not the only way to use a CRT, see e.g. [https://en.wikipedia.org/wiki/Vector_monitor vector monitors], and CRT oscilloscopes are also interesting, but it's a good way to do a generic display)}}


In theory yes, but even if that didn't imply an insane amount of wires (it does), it may not be worth it.
So yes, a TV and CRT monitor is essentially updated one pixel at a time, which happens so fast you would need a ''very'' fast camera
to notice this - see e.g. [https://youtu.be/3BJU2drrtCM?t=52].


Transferring millions of numbers takes time, meaning that to update everything at once you need to wait until you've stored all of it,
This means that there needs to be something that controls the left-to-right and top-to-bottom steering[https://youtu.be/l4UgZBs7ZGo?t=307] - and because you're really just bending it back and forth, there are also times at which that bending shouldn't be visible, which is solved by just not emitting electrons, called the blanking intervals. If you didn't have horizontal blanking interval between lines, you would see nearly-horizontal lines as it gets dragged back for the next line; if you didn't have vertical blanking interval between frames you would see a diagonal line while it gets dragged back to the start of the next frame.
and you've gained nothing in terms of speed. You're arguably losing speed because instead of updating lines as the data comes in, you're choosing to wait until you have it all.


You would also need to get communication that can go much much faster (and sits idle most of the time).
In CRTs monitors, '''hsync''' and '''vsync''' names signals that (not control it directly but) help that movement happen.




The per-line tradeoff described above makes much more sense for multiple reasons.
CRTs were driven relatively directly from the graphics card, in the sense that the values of the pixel we're beaming onto a pixel will be the value that is on the line ''at that very moment''.
Do things ''more or less'' live,
It would be hard and expensive to do any buffering, and there would be no reason (the phosphor's short term persistance is a buffer of sorts).  
but do it roughly one line at a time - we can do it ''sooner'',
it requires less storage,
we can do it over dozens to hundreds of lines to the actual panel.


So there needs to be a precisely timed stream of pixel data that is passed to the phosphors,
and you spend most of the interval drawing pixels (all minus the blanking parts).}}






'''If you can address lines at a time, you could you do partial updates this way?'''
'''How are CRT monitors different from CRT TVs?'''


Yes. And that exists.
In TVs, redraw speeds were basically set in stone, as were some decoding details.
But it turns out there are few cases where this tradeoff is actually useful.
It was still synchronized from the signal, but the speed was basically fixed, as that made things easier.


And now you also need some way to keep track of what parts (not) to update,
On color TV there were some extra details, but a good deal worked the same way.


which tends to mean either a very simple UI, or an extra framebuffer
Early game consoles/computers just generated a TV signal, so that you could use the TV you already had.


e.g. Memory LCD is somewhat like e-paper, but it's 1-bit, mostly gets used in status displays{{verify}},
After that, CRT monitors started out as adapted CRT TVs.
Around games and TVs it is rare that less than the whole screen changes,  
Yet we were not tied to the broadcast format,
so it didn't take long at all before speed at which things are drawn was configurable.
By the nineties it wasn't too unusual to drive a CRT monitor at 56, 60, 72, 75, perhaps 85, and sometimes 90{{verify}}, 100, or 120Hz.


Some browser/office things are mostly static - except when you scroll.
We also grew an increasing amount of resolutions that the monitor should be capable of displaying.
Or rather, resolution-refresh combinations. Detecting and dealing that is a topic in and of itself.


}}


Yet at the CRT level, they were driven much the same way -
synchronization timing to let the monitor know when and how fast to sweep the beams around,
and a stream of pixels passed through as they arrive on the wires.


So a bunch of the TV mechanism lived on into CRT monitors - and even into the flatscreen era.


That means that at, say, 60fps, roughly 16.6 milliseconds per frame,
''most'' of that 16ms is spent moving values onto the wire and onto the screen.






''' 'What to draw' influenced this development too'''


When in particular the earliest gaming consoles were made, RAM was expensive.
'''How are flatscreens different from CRTs?'''
A graphics chip (and sometimes just the CPU) could draw something as RAM-light as sprites, if it was aware of where resolution-wise it was drawing right now.
It has to be said there were some ''very'' clever ways those were abused over time, but at the same time, this was also why the earliest gaming had limits like 'how many sprites could be on screen at once and maybe not on the same horizontal lines without things going weird'.


The physical means of display is completely different.


In particular PCs soon switched to framebuffers, meaning "a screenful of pixels on the PC side that you draw into", and the graphics card got a dedicated to sending that onto a wire (a [https://en.wikipedia.org/wiki/RAMDAC RAMDAC], basically short for 'hardware that you point at a framebuffer and spits out voltages, one for each pixel color at a time'). This meant we could draw anything, meant we had more time to do the actual drawing, and made higher resolutions a little more practical (if initially still limited by RAM cost).  In fact, VGA as a connector carries very little more than hsync, vsync, and "the current pixel's r,g,b", mostly just handled by the RAMDAC.
There is a constant backlight, and from the point of view of a single LCD pixel,  
the crystal's blocking-or-not state will sit around until asked to change.




And yet the sending-pixels part is still much the same.
Consider that a ''single'' frame is millions of numbers (e.g. 1920 * 1080 * 3 colors ~= 6 million).
For PCs with color this was never much under a million.


======Screen tearing and vsync======
Regardless of how many colors,
actually just transferring that many individual values will take some time.




'''When to draw'''
The hsync and vsync signals still exist,
though LCDs are often a little more forgiving, apparently keeping a short memory and allowing some syncing [https://youtu.be/muuhgrige5Q?t=425]
 


So, the graphics card has the job of sending 'start new frame' and the stream of pixels.


You ''could'' just draw into the framebuffer whenever,
Does a monitor have a framebuffer and then update everything at once?
but if that bears no relation to when the graphics card sends new frames,
It ''could'' be designed that way if there was a point, but there rarely is.
it would happen ''very easily'' that you are drawing into the framebuffer while the video card is sending it to the screen,
It would only make things more expensive for no reason.
and would shown a half-drawn image.




While in theory a program could learn the time at which to ''not'' draw, it turns out that's relatively little of all the time you have.
When the only thing we are required to do is to finish drawing one image before the next starts,
then we can spend most of that time sending pixels,
and the screen, while it has more flexibility in ''how'' exactly, can spend most of the refresh interval updating pixels.
...basically as in the CRT days.




One of the simplest ways around that is '''double buffering''':
And when we were using VGA on flatscreens, that was what we were doing.
: have one image that the graphics card is currently showing,  
: have one hidden next one that you are drawing to
: tell the graphics card to switch to the other when you are done


Panels even tend to update a line at a time.


This also means the program doesn't really need to learn this hardware schedule at all:
Why?
Whenever you are done drawing, you tell the graphics card to flip to the other one.
: the ability to update specific pixels would require a lot more wiring - a per-line addressing is already a good amount of wires (there is a similar tradeoff in camera image sensor readout, but in the other direction)
: LCDs need to be refreshed somewhat like DRAM (LCD doesn't like being held at a constant voltage, so monitors apply the pixel voltage in alternating polarities each frame. (This is not something you really need to worry about. [http://www.techmind.org/lcd/index.html#inversion It needs an ''extremely'' specifc image to see])).




How do we keep it in step? Varies, actually, due to some other practical details.


Scanout itself basically refers to the readout and transfer of the framebuffer on the PC side,


Roughly speaking,
'''Scanout lag''' can refer to
: vsync on means "wait to flip the buffers until you are between frames"
: the per-line update
: vsync off means "show new content as soon as possible, I don't care about tearing",
: the lag in pixel change, GtG stuff
:




You can find some high speed footage of a monitor updating, e.g. [https://blurbusters.com/understanding-display-scanout-lag-with-high-speed-video here]
which illustrates terms like [[GtG]] (and why they both are and are not a sales trick):
Even if a lines's values are updated in well under a millisecond, the pixels may need ~5ms to settle on their new color,
and seen at high speeds, this looks like a range of the screen is a blur between the old and new image.


In the latter case, you will often see part of two different images. They will now always be ''completely drawn'' images,
and they will usually resemble each other,
but on fast moving things you will just about see the fact that there was a cut point for a split second.


If the timing of drawing and monitor draw is unrelated, this will be at an unpredictable position.
This is arguably a feature, because if this happens regularly (and it would), it happens at different positions all the time,
which is less visible than if they are very near each other (it would seem to slowly move).


'''Would it not be technically possible to update all this-many million pixels at the same time? '''


In theory yes, but even if that didn't imply an insane amount of wires (it does), it may not be worth it.


Gamers may see vsync as a framerate cap, but that's mainly just because it would be entirely pointless to render more frames than you can show,
Transferring millions of numbers takes time, meaning that to update everything at once you need to wait until you've stored all of it,
(unless it's winter and you are using your GPU as a heater).
and you've gained nothing in terms of speed.


You're arguably losing speed because instead of updating lines as the data comes in, you're choosing to wait until you have it all.


You would also need to get communication that can go so much faster that it moves a frame multiples faster and sits idle most of the time.


----
That too is possible - but would only drive up cost.




'''Does that mean it's updating pixels while you're watching rather than all at once?'''
The per-line tradeoff described above makes much more sense for multiple reasons.
Do things ''more or less'' live,
but do it roughly one line at a time - we can do it ''sooner'',
it requires less storage,
we can do it over dozens to hundreds of lines to the actual panel.


Yes.


Due to the framerate alone it's still fast enough that you wouldn't notice.
As that slow mo video linked above points out, you don't even notice that your phone screen is probably updating sideways.




Note that while in VGA, the pixel update is fixed by the PC,
'''If you can address lines at a time, you could you do partial updates this way?'''
in the digital era we are a little less tied.


In theory, we could send the new image ''much'' faster than the speed at which the monitor can update itself,
Yes. And that exists.
but in practice, you don't really gain anything by doing so.
But it turns out there are few cases where this tradeoff is actually useful.


And now you also need some way to keep track of what parts (not) to update,


which tends to mean either a very simple UI, or an extra framebuffer


e.g. Memory LCD is somewhat like e-paper, but it's 1-bit, mostly gets used in status displays{{verify}},
Around games and TVs it is rare that less than the whole screen changes,


'''Does that mean it takes time from the first pixel change to the last pixel change within a frame? Like, over multiple microseconds?'''
Some browser/office things are mostly static - except when you scroll.


Yes. Except it's over multiple ''milliseconds''.
}}


Just how many milliseconds varies, with the exact way the panel works, but AFAICT not a lot.


I just used some phototransistors to measure that one of my (HDMI) monitors at 60Hz takes approximately 14ms to get from the top to the bottom.








''' 'What to draw' influenced this development too'''


When in particular the earliest gaming consoles were made, RAM was expensive.
A graphics chip (and sometimes just the CPU) could draw something as RAM-light as sprites, if it was aware of where resolution-wise it was drawing right now.
It has to be said there were some ''very'' clever ways those were abused over time, but at the same time, this was also why the earliest gaming had limits like 'how many sprites could be on screen at once and maybe not on the same horizontal lines without things going weird'.


---


There would be little point to keeping a coping of an entire screen, since we're reading from a framebuffer just as before.  
In particular PCs soon switched to framebuffers, meaning "a screenful of pixels on the PC side that you draw into", and the graphics card got a dedicated to sending that onto a wire (a [https://en.wikipedia.org/wiki/RAMDAC RAMDAC], basically short for 'hardware that you point at a framebuffer and spits out voltages, one for each pixel color at a time'). This meant we could draw anything, meant we had more time to do the actual drawing, and made higher resolutions a little more practical (if initially still limited by RAM cost).  In fact, VGA as a connector carries very little more than hsync, vsync, and "the current pixel's r,g,b", mostly just handled by the RAMDAC.
It would in fact be simpler and more immediate to just tell the LCD controller where that framebuffer is, and what format it is in.


Note that while this is different mechanism, it has almost no visible effect on tearing.


(on-screen displays seem like they draw on top of a framebuffer, particularly when they are transparent, but this can be done on the fly)


https://www.nxp.com/docs/en/application-note/AN3606.pdf
======Screen tearing and vsync======




'''When to draw'''


'''Are flatscreen TVs any different?'''
So, the graphics card has the job of sending 'start new frame' and the stream of pixels.


Depends.  
You ''could'' just draw into the framebuffer whenever,
but if that bears no relation to when the graphics card sends new frames,
it would happen ''very easily'' that you are drawing into the framebuffer while the video card is sending it to the screen,
and would shown a half-drawn image.


Frequently yes, because a lot are sold with some extra Fancy Processing&tm;, like interpolation in resolution and/or time,
which by the nature of these features ''must'' have some amount of framebuffer.
This means the TV could be roughly seen as a PC with a capture card: it keeps image data around, then does some processing before it
gets sent to the display (which happens to physically be in the same bit of plastic))


While in theory a program could learn the time at which to ''not'' draw, it turns out that's relatively little of all the time you have.


And that tends to add a few to a few dozen milliseconds.
Which doesn't matter to roughly ''anything'' in TV broadcast. There was a time at which different houses would cheer at different times for the same sports goal, but ''both'' were much further away from the actual event than to each other. It just doesn't matter.


One of the simplest ways around that is '''double buffering''':
So if they having a "gaming mode", that usually means "disable that processing".
: have one image that the graphics card is currently showing,  
: have one hidden next one that you are drawing to
: tell the graphics card to switch to the other when you are done




This also means the program doesn't really need to learn this hardware schedule at all:
Whenever you are done drawing, you tell the graphics card to flip to the other one.




'''Are there other ways of updating?'''
How do we keep it in step? Varies, actually, due to some other practical details.


Yes. Phones have been both gearhead country and battery-motivated territory for a while
so have also started going 120Hz or whatnot.


At the same time, they may figure out that you're staring at static text,  
Roughly speaking,
so they may refresh the framebuffer and/or screen ''much'' less often.
: vsync on means "wait to flip the buffers until you are between frames"
: vsync off means "show new content as soon as possible, I don't care about tearing",






'''Is OLED different?'''
In the latter case, you will often see part of two different images. They will now always be ''completely drawn'' images,
and they will usually resemble each other,
but on fast moving things you will just about see the fact that there was a cut point for a split second.


No and yes.
If the timing of drawing and monitor draw is unrelated, this will be at an unpredictable position.
This is arguably a feature, because if this happens regularly (and it would), it happens at different positions all the time,
which is less visible than if they are very near each other (it would seem to slowly move).


And it seems it's not so much differen ''because'' it's OLED specifically,
but because these new things correlated with a time of new design goals and new experiments{{verify}}


https://www.youtube.com/watch?v=n2Qj40zuZQ4


Gamers may see vsync as a framerate cap, but that's mainly just because it would be entirely pointless to render more frames than you can show,
(unless it's winter and you are using your GPU as a heater).


-->


=====On pixel response time and blur=====
<!--
So, each pixel cannot change its state instantly. It's on the order of a few milliseconds.


There are various metrics, like
----
* GtG (Gray To Gray)
* BwB (black-white-black)
* WbW (white-black-white)


None of these are standardized, vendors measure them differently, and you can assume as optimistically as possible for their specs page, so these are not very comparable.


'''Does that mean it's updating pixels while you're watching rather than all at once?'''


This also implies that a given framerte will look slightly different on different monitors - because pixels having to change more than they can looks like blur.
Yes.
: this matters more to high contrast (argument for BwB, WbW)
: but most of most images isn't high contrast (argument for GtG)


Due to the framerate alone it's still fast enough that you wouldn't notice.
As that slow mo video linked above points out, you don't even notice that your phone screen is probably updating sideways.


One way to work around this, on a technical level, is higher framerate.
''Display'' framerate, that is{{verify}}.


On paper this works, but it is much less studied and less clear to which degree this is just the current sales trick, versus to what degree it actually looks better.
Note that while in VGA, the pixel update is fixed by the PC,  
in the digital era we are a little less tied.  


In fact, GtG seems by nature a sales trick. Yes there's a point to it because it's a curve, but at the same time it's a figure that is easily half of the other two, that you can slap on your box.
In theory, we could send the new image ''much'' faster than the speed at which the monitor can update itself,
but in practice, you don't really gain anything by doing so.




It's also mentioned because it's one possible factor in tracking.


-->


====What Vsync adds====
'''Does that mean it takes time from the first pixel change to the last pixel change within a frame? Like, over multiple microseconds?'''


<!--
Yes. Except it's over multiple ''milliseconds''.


Just how many milliseconds varies, with the exact way the panel works, but AFAICT not a lot.


As the above notes, we push pixels to the framebuffer as fast as we can, a monitor just shows what it gets (at what is almost always a fixed framerate = fixed schedule).
I just used some phototransistors to measure that one of my (HDMI) monitors at 60Hz takes approximately 14ms to get from the top to the bottom.


''Roughly'' speaking, every 16ms, the video card signals it's sending a new frame, and sends whatever data is in its framebuffer as it sends it.




And it has no inherent reason to care whatever else is happening.


So if you changed that framebuffer while it was being sent out, the from the perspective of entire frames, it didn't sent full, individual ones.
: It is possible that it sent part of the previous and part of a next frame.
: It is possible that it sent something that looks wrong because it wasn't fully done drawing (this further depends a little on ''how'' you are drawing)




It's lowest latency to get things on screen, but can look incorrect.
---


There would be little point to keeping a coping of an entire screen, since we're reading from a framebuffer just as before.
It would in fact be simpler and more immediate to just tell the LCD controller where that framebuffer is, and what format it is in.


Note that while this is different mechanism, it has almost no visible effect on tearing.


There are two common ingredients to the solution:
(on-screen displays seem like they draw on top of a framebuffer, particularly when they are transparent, but this can be done on the fly)


* vsync in the sense of waiting until we are between frames
https://www.nxp.com/docs/en/application-note/AN3606.pdf
:: The above describes the situation without vsync, or with vsync off. This is the most immediate, "whenever you want" / "as fast as possible" way.
:: '''With vsync on''', the change of the image to send from is closely tied to when we tell/know the monitor is between frames.
:: It usually amounts to the software ''waiting'' until the graphics card is between frames. That doesn't necessarily solve all the issues, though. In theory you could do all your drawing in that inbetween time, but it's not a lot of time.


* double buffering
:: means we have two framebuffers: one that is currently being sent to the screen, and one we are currently drawing to
:: and at some time we tell the GPU to switch between the two




Double buffering with vsync off means ''switch as soon as we're done drawing''.
'''Are flatscreen TVs any different?'''
It solves the incomplete-drawing problem, and is fast in the sense that it otherwise doesn't wait to get things on screen.


But we still allow that to be in the middle of the monitor pixels being sent out, so it can switch images in the middle of a frame.  
Depends.  


If those software flips are at a time unrelated to hardware, and/or images were very similar anyway (slow moving game, non-moving office document),
Frequently yes, because a lot are sold with some extra Fancy Processing&tm;, like interpolation in resolution and/or time,  
then this discontinuity is ''usually'' barely visible, because either the frames tend to look very similar,  
which by the nature of these features ''must'' have some amount of framebuffer.
or it happens at random positions on the screen, or both.
This means the TV could be roughly seen as a PC with a capture card: it keeps image data around, then does some processing before it
gets sent to the display (which happens to physically be in the same bit of plastic))


It is only when this split-of-sorts happens is in a similar place (fast movement, regular and related update schedule, which can come from rendering a lot faster than monitor) that it is consistent enough to notice, and we call it '''screen tearing''', because it looks something like a torn photo taped back together without care to align it. Screen tearing is mostly visible with video and with games, and mostly with horizontal motion (because of the way most the update is by line).


It's still absolutely there in more boring PC use, but it's just less visible because what you are showing is a lot more static.
And that tends to add a few to a few dozen milliseconds.
Also the direction helps - I put one one my monitors vertical, and the effect is visible when I scroll webpages because this works out as a broadly visible skew, more noticeable than taller/shorter letters that I'm not reading at that moment anyway.
Which doesn't matter to roughly ''anything'' in TV broadcast. There was a time at which different houses would cheer at different times for the same sports goal, but ''both'' were much further away from the actual event than to each other. It just doesn't matter.


So if they having a "gaming mode", that usually means "disable that processing".


So the most proper choice is vsync on ''and'' '''double buffering'''. With this combination:
* we have two framebuffers that we flip between
* we flip them when the video card is between frames






'''vsync is also rate limiting. And in a integer division way.'''
'''Are there other ways of updating?'''


Another benefit to vsync on is that we don't try to render faster than necessary.  
Yes. Phones have been both gearhead country and battery-motivated territory for a while
60Hz screen? We will be sending out 60 images per second.
so have also started going 120Hz or whatnot.


...well, ''up to'' 60. Because we wait until a new frame, that means a very regular schedule that we have no immediate control over.  
At the same time, they may figure out that you're staring at static text,
so they may refresh the framebuffer and/or screen ''much'' less often.


At 60Hz, you need to finish a new frame within 16.67ms (1 second / 60).
Did you take 16.8ms? Then you missed it, and the previous frame will stay on screen for another 16.67ms.




For example, 60Hz will mean that if
'''Is OLED different?'''
: 16.6ms (60fps)
: 1 frame late means it has to come 33.3ms after the start instead, which you could say is momentarily 30fps (60/2)
: 2 frames late is 50ms later, for 20fps (60/3)
: 3 frames late is 66ms later, for 15fps (60/4)
: ...and so on, but we're already in "looks terrible" territory.


No and yes.


So assuming things are a little late, do we get locked into 30fps instead?
And it seems it's not so much differen ''because'' it's OLED specifically,
but because these new things correlated with a time of new design goals and new experiments{{verify}}


Well, no. Or rather, that depends on whether you are CPU-bound or GPU-bound.  
https://www.youtube.com/watch?v=n2Qj40zuZQ4
If the GPU is a little too slow to get each frame in on time, then chances are it's closer to 30fps.
If the GPU is fast enough but the CPU


The difference exists in part because the GPU not having enough time is a ''relatively'' fixed problem
because
it mostly just has one job (of relatively-slowly varying complexity)
and drawing the next frame is often timed since the last
while
the CPU being late is often more variable,
but even if it weren't and it's on its own rate,


-->


And even that varies on the way the API works.
=====On pixel response time and blur=====
: OpenGL and D3D11 - GPU won't start rendering until vsync releases a buffer to render ''into''  {{verify}}
<!--
: Vulkan and D3D12 - such backpressure has to be done explicitly and differently {{verify}}
So, each pixel cannot change its state instantly. It's on the order of a few milliseconds.


There are various metrics, like
* GtG (Gray To Gray)
* BwB (black-white-black)
* WbW (white-black-white)


None of these are standardized, vendors measure them differently, and you can assume as optimistically as possible for their specs page, so these are not very comparable.


(side note: A game's FPS counter indicating only the interval of the last frame would update too quickly to see, so FPS counters tend to show a recent average)


vsync means updatesg only happen at multiples of that basic time interval,
This also implies that a given framerte will look slightly different on different monitors - because pixels having to change more than they can looks like blur.
meaning immediate framrerates that are integer divisions of the native rate.
: this matters more to high contrast (argument for BwB, WbW)
: but most of most images isn't high contrast (argument for GtG)


To games, vsync is sort of bad, in that if you ''structurally'' take more than 16.8ms aiming for 60Hz,
you will be running at a solid 30fps, not something inbetween 30 and 60.
When you ''could'' be rendering at 50 and showing most of that information,
there are games where that immediacy is worth it regardless of the tearing.


For gamers, vsync is only worth it if you can keep the render solidly at the monitor rate.
One way to work around this, on a technical level, is higher framerate.
''Display'' framerate, that is{{verify}}.


On paper this works, but it is much less studied and less clear to which degree this is just the current sales trick, versus to what degree it actually looks better.


In fact, GtG seems by nature a sales trick. Yes there's a point to it because it's a curve, but at the same time it's a figure that is easily half of the other two, that you can slap on your box.




Notes:
It's also mentioned because it's one possible factor in tracking.
: vsync this is not the same mechanism as double buffering, but it is certainly related


-->


====Vsync====


<!--


What vsync adds




'''Related things'''
As the above notes, we push pixels to the framebuffer as fast as we can, a monitor just shows what it gets (at what is almost always a fixed framerate = fixed schedule).
Pointing a camera at a screen gives the same issue, because that camera will often be running at a different rate.
Actually, the closer it is, the slower the tearing will seem to move - which is actually more visible.


This was more visible on CRTs because the falloff of the phosphor brightness (a bunch of it in 1-2ms) is more visible the shorter the camera's exposure time was. There are new reasons that make this visible in other situations, like [[rolling shutter]].
''Roughly'' speaking, every 16ms, the video card signals it's sending a new frame, and sends whatever data is in its framebuffer as it sends it.




Screen capture, relevant in these game-streaming days, may be affected by vsync in the same way.
And it has no inherent reason to care whatever else is happening.  
It's basically a ''third'' party looking at the same frame data, so another thing to ''independently'' have such tearing and/or slowdown issues.


So if you changed that framebuffer while it was being sent out, the from the perspective of entire frames, it didn't sent full, individual ones.
: It is possible that it sent part of the previous and part of a next frame.
: It is possible that it sent something that looks wrong because it wasn't fully done drawing (this further depends a little on ''how'' you are drawing)




It's lowest latency to get things on screen, but can look incorrect.




====Vsync====


Intuitively, vsync tells the GPU to wait until refresh.
There are two common ingredients to the solution:


* vsync in the sense of waiting until we are between frames
:: The above describes the situation without vsync, or with vsync off. This is the most immediate, "whenever you want" / "as fast as possible" way.
:: '''With vsync on''', the change of the image to send from is closely tied to when we tell/know the monitor is between frames.
:: It usually amounts to the software ''waiting'' until the graphics card is between frames. That doesn't necessarily solve all the issues, though. In theory you could do all your drawing in that inbetween time, but it's not a lot of time.


This is slightly imprecise, in a way that matters later.
* double buffering
What it's really doing is telling the GPU to flip buffers until the next refresh.
:: means we have two framebuffers: one that is currently being sent to the screen, and one we are currently drawing to
:: and at some time we tell the GPU to switch between the two




In theory, we could still be rendering multiples more frames,  
Double buffering with vsync off means ''switch as soon as we're done drawing''.
and only putting out some to the monitor.
It solves the incomplete-drawing problem, and is fast in the sense that it otherwise doesn't wait to get things on screen.  


But there is typically no good reason to do so,  
But we still allow that to be in the middle of the monitor pixels being sent out, so it can switch images in the middle of a frame.  
so enabling vsync usually comes with reducing the render rate to the refresh rate.


If those software flips are at a time unrelated to hardware, and/or images were very similar anyway (slow moving game, non-moving office document),
then this discontinuity is ''usually'' barely visible, because either the frames tend to look very similar,
or it happens at random positions on the screen, or both.
It is only when this split-of-sorts happens is in a similar place (fast movement, regular and related update schedule, which can come from rendering a lot faster than monitor) that it is consistent enough to notice, and we call it '''screen tearing''', because it looks something like a torn photo taped back together without care to align it. Screen tearing is mostly visible with video and with games, and mostly with horizontal motion (because of the way most the update is by line).


Similarly, disabling vsync does not ''necessarily'' uncap your framerate, because developers may
It's still absolutely there in more boring PC use, but it's just less visible because what you are showing is a lot more static.
have other reasons to throttle frames.
Also the direction helps - I put one one my monitors vertical, and the effect is visible when I scroll webpages because this works out as a broadly visible skew, more noticeable than taller/shorter letters that I'm not reading at that moment anyway.




So the most proper choice is vsync on ''and'' '''double buffering'''. With this combination:
* we have two framebuffers that we flip between
* we flip them when the video card is between frames




'''Vsync when the frames come too fast''' is a fairly easy decision,
because we only tell the GPU to go no faster than the screen's refresh rate.


The idea being that there's no point in trying to have things to draw faster than we can draw them.
'''vsync is also rate limiting. And in a integer division way.'''
It just means more heat drawing things we mostly don't see.


In this case, with vsync off you may see things ''slightly'' earlier,
Another benefit to vsync on is that we don't try to render faster than necessary.
But it can be somewhat visually distracting, and the difference in timing may not be enough to matter.
60Hz screen? We will be sending out 60 images per second.


Unless you're doing competition, you may value aesthetics more than reaction.
...well, ''up to'' 60. Because we wait until a new frame, that means a very regular schedule that we have no immediate control over.  


At 60Hz, you need to finish a new frame within 16.67ms (1 second / 60).
Did you take 16.8ms? Then you missed it, and the previous frame will stay on screen for another 16.67ms.




For example, 60Hz will mean that if
: 16.6ms (60fps)
: 1 frame late means it has to come 33.3ms after the start instead, which you could say is momentarily 30fps (60/2)
: 2 frames late is 50ms later, for 20fps (60/3)
: 3 frames late is 66ms later, for 15fps (60/4)
: ...and so on, but we're already in "looks terrible" territory.


'''Vsync when the frames come in slower than the monitor refresh rate''' is another matter.


Vsync still means the same thing -- "GPU, wait to display an image at monitor refresh time".
So assuming things are a little late, do we get locked into 30fps instead?
But note that slower-than-refresh rendering means we are typically too late for a refresh,  
 
so this will make it wait even longer.
Well, no. Or rather, that depends on whether you are CPU-bound or GPU-bound.
If the GPU is a little too slow to get each frame in on time, then chances are it's closer to 30fps.
If the GPU is fast enough but the CPU


The difference exists in part because the GPU not having enough time is a ''relatively'' fixed problem
because
it mostly just has one job (of relatively-slowly varying complexity)
and drawing the next frame is often timed since the last
while
the CPU being late is often more variable,
but even if it weren't and it's on its own rate,


Say, if we have a 60Hz screen (16.7ms interval) and 50fps rendering (20ms interval),


* if you start a new frame render after the previous one got displayed, you will miss every second frame, and be displaying at 30fps.
And even that varies on the way the API works.
: OpenGL and D3D11 - GPU won't start rendering until vsync releases a buffer to render ''into''  {{verify}}
: Vulkan and D3D12 - such backpressure has to be done explicitly and differently {{verify}}


* if you render independently, then we will only occasionally be late, and leave a frame on screen for two intervals rather than one




(side note: A game's FPS counter indicating only the interval of the last frame would update too quickly to see, so FPS counters tend to show a recent average)


You can work this out on paper, but it comes down to that it will run at an integer divisor of the framerate.
vsync means updatesg only happen at multiples of that basic time interval,
meaning immediate framrerates that are integer divisions of the native rate.


So if rendering dips a little below 60fps, it's now displaying at 30fps (and usually only that. Yes, the next divisors are 20, 15, 12, 10, but below 30fps people will whine ''regardless' vsync. Also, the difference is lower). This is one decent reason gamers dislike vsync, and one decent reason to aim for 60fps and more - even if you don't get it, your life will be predictably okay.
To games, vsync is sort of bad, in that if you ''structurally'' take more than 16.8ms aiming for 60Hz,
you will be running at a solid 30fps, not something inbetween 30 and 60.
When you ''could'' be rendering at 50 and showing most of that information,
there are games where that immediacy is worth it regardless of the tearing.


For gamers, vsync is only worth it if you can keep the render solidly at the monitor rate.




And depending on how much lower, then the sluggishness may be more visible than a little screen tearing.
This also seems like an unnecessary slowdown


Say a game is aiming at 60fps and usually ''almost'' managing. You might prefer vsync off.


Notes:
: vsync this is not the same mechanism as double buffering, but it is certainly related




TODO: read [https://hardforum.com/threads/how-vsync-works-and-why-people-loathe-it.928593/]






'''Adaptive VSync'''


If the fps is higher than the refresh, VSync is enabled,
'''Related things'''
if the fps is lower than the monitor refresh, it's disabled.
Pointing a camera at a screen gives the same issue, because that camera will often be running at a different rate.
Actually, the closer it is, the slower the tearing will seem to move - which is actually more visible.


This avoids
This was more visible on CRTs because the falloff of the phosphor brightness (a bunch of it in 1-2ms) is more visible the shorter the camera's exposure time was. There are new reasons that make this visible in other situations, like [[rolling shutter]].




'''NVidia Fast Sync''' / '''AMD Enhanced Sync'''
Screen capture, relevant in these game-streaming days, may be affected by vsync in the same way.
It's basically a ''third'' party looking at the same frame data, so another thing to ''independently'' have such tearing and/or slowdown issues.


Adaptive VSync that adds triple buffering to pick.


Useful when you have more than enough GPU power.






====Vsync====


Intuitively, vsync tells the GPU to wait until refresh.


Note that with vsync on, whenever you are late for a frame at the monitor's framerate, you really just leave the image on an extra interval. Or two.


This is why it divides the framerate by integer multiples. If on a 60Hz monitor it stays on for one frame it's 60fps, for two frames it's 30fps, for three frames it's 20fps, for four frames it's 15fps, etc.
This is slightly imprecise, in a way that matters later.  
What it's really doing is telling the GPU to flip buffers until the next refresh.  


When with vsync on that FPS counter says something like 41fps, it really means "the average over tha last bunch of frames was a mix of updates happening at 16ms/60fps intervals, but more happening at 32/30fps" (and maybe occasionally lower).


In theory, we could still be rendering multiples more frames,
and only putting out some to the monitor.


'''Could it get any more complex?'''
But there is typically no good reason to do so,
so enabling vsync usually comes with reducing the render rate to the refresh rate.


Oh, absolutely!


'''I didn-'''
Similarly, disabling vsync does not ''necessarily'' uncap your framerate, because developers may
have other reasons to throttle frames.
 
 
 
 
'''Vsync when the frames come too fast''' is a fairly easy decision,
because we only tell the GPU to go no faster than the screen's refresh rate.
 
The idea being that there's no point in trying to have things to draw faster than we can draw them.
It just means more heat drawing things we mostly don't see.
 
In this case, with vsync off you may see things ''slightly'' earlier,
But it can be somewhat visually distracting, and the difference in timing may not be enough to matter.
 
Unless you're doing competition, you may value aesthetics more than reaction.
 
 
 
 
'''Vsync when the frames come in slower than the monitor refresh rate''' is another matter.
 
Vsync still means the same thing -- "GPU, wait to display an image at monitor refresh time".
But note that slower-than-refresh rendering means we are typically too late for a refresh,
so this will make it wait even longer.
 


...you see, the GPU is great at independently drawing complex things from relatively simple descriptions, but something still needs to tell it to that.
Say, if we have a 60Hz screen (16.7ms interval) and 50fps rendering (20ms interval),
And a game will have a bunch of, well, game logic, and often physics that needs to be calculated before we're down to purely ''visual'' calculations.


Point is that with that involved, you can now also be CPU-limited. Maybe the GPU can ''draw'' what it gets at 200fps but the CPU can only figure out new things to draw at around 40fps. Which means a mix of 60 and 30fps as just mentioned. And your GPU won't get very warm because it's idling most of the time.  
* if you start a new frame render after the previous one got displayed, you will miss every second frame, and be displaying at 30fps.
Games try to avoid this, but [some people take that as a challenge].
 
 
* if you render independently, then we will only occasionally be late, and leave a frame on screen for two intervals rather than one
 
 
 
 
-->
 
 
You can work this out on paper, but it comes down to that it will run at an integer divisor of the framerate.
====Adaptive sync====
 
<!--
So if rendering dips a little below 60fps, it's now displaying at 30fps (and usually only that. Yes, the next divisors are 20, 15, 12, 10, but below 30fps people will whine ''regardless' vsync. Also, the difference is lower). This is one decent reason gamers dislike vsync, and one decent reason to aim for 60fps and more - even if you don't get it, your life will be predictably okay.
 
 
Where most monitors keep a regular schedule (and set it themselves).
 
 
 
Nvidia G-sync and AMD Freesync treats frame length them as varying.
And depending on how much lower, then the sluggishness may be more visible than a little screen tearing.
 
This also seems like an unnecessary slowdown
 
 
Note that doing this requires both a GPU and monitor that support this.  
Say a game is aiming at 60fps and usually ''almost'' managing. You might prefer vsync off.
 
 
 
TODO: read [https://hardforum.com/threads/how-vsync-works-and-why-people-loathe-it.928593/]
 
 
 
'''Adaptive VSync'''
 
If the fps is higher than the refresh, VSync is enabled,
if the fps is lower than the monitor refresh, it's disabled.
 
This avoids
 
 
'''NVidia Fast Sync''' / '''AMD Enhanced Sync'''
 
Adaptive VSync that adds triple buffering to pick.
 
Useful when you have more than enough GPU power.
 
 
 
 
 
Note that with vsync on, whenever you are late for a frame at the monitor's framerate, you really just leave the image on an extra interval. Or two.
 
This is why it divides the framerate by integer multiples. If on a 60Hz monitor it stays on for one frame it's 60fps, for two frames it's 30fps, for three frames it's 20fps, for four frames it's 15fps, etc.
 
When with vsync on that FPS counter says something like 41fps, it really means "the average over tha last bunch of frames was a mix of updates happening at 16ms/60fps intervals, but more happening at 32/30fps" (and maybe occasionally lower).
 
 
'''Could it get any more complex?'''
 
Oh, absolutely!
 
'''I didn-'''
 
...you see, the GPU is great at independently drawing complex things from relatively simple descriptions, but something still needs to tell it to that.
And a game will have a bunch of, well, game logic, and often physics that needs to be calculated before we're down to purely ''visual'' calculations.
 
Point is that with that involved, you can now also be CPU-limited. Maybe the GPU can ''draw'' what it gets at 200fps but the CPU can only figure out new things to draw at around 40fps. Which means a mix of 60 and 30fps as just mentioned. And your GPU won't get very warm because it's idling most of the time.  
Games try to avoid this, but [some people take that as a challenge].
 
 
 
-->
 
====Adaptive sync====
<!--
{{stub}}
 
For context, most monitors keep a regular schedule (and set it themselves{{verify}}).
 
Nvidia G-sync and AMD Freesync treats frame length them as varying.
 
 
Basically, the GPU sending a new frame will make the monitor start updating it as it comes in,
rather than on the next planned interval.
 
 
Manufacturer marketing as well as reviewers seem very willing to imply
: vague "increases input lag dramatically" and the way they say it is often just ''wrong'', or
: "do you want to solve tearing ''without'' the framerate cap that vsync implies" and it's a pity that's pointing out the ''wrong'' issue about vsync,
: "G-Sync has better quality than FreeSync", whatever that means
 
A more honest way of putting it might be
"when frames come in slower than the monitor's maximum,
we go to the actual render rate, without tearing"
 
...rather than the integer-division ''below'' the actual render rate (if you have vsync on)
or sort of the actual render rate but with tearing (with vsync on).
 
There's absolutely value to that, but dramatic? Not very.
 
 
 
Note that doing this requires both a GPU and monitor that support this.  
 
Which so far, for monitors, is a gamer niche.
 
 
And the two mentioned buzzwords are not compatible with each other.
 
For some reason, most articles don't get much further than
"yeah G-sync is fancier and more expensive and freesync is cheaper and good enough (unless you fall under 30fps which you want to avoid anyway)"
 
...and tend to skip ''why'' (possibly related that the explanation behind stuttering is often a confused ''mess'').
 
 
 
Note that while it can show frames as soon as your GPU has them, it doesn't go beyond a maximum rate.
So that Hz rate is essentially its ''maximum'', and it will frequently go slower.
 
It seems to mean that the PC can instruct the monitor to start a new frame whenever it wants.
The monitor's refresh rate is now effectively the ''maximum''.
 
 
This in particular avoids the 'unnecessary further drop when frames come in slower than the monitor refresh rate'


Which so far is a gamer niche.
And the two mentioned buzzwords are not compatible with each other,
but for some reason, most articles don't get much further than
"yeah G-sync is fancier and more expensive and freesync is cheaper and good enough (unless you fall under 30fps which you want to avoid anyway)" and tend to completely forego ''why'' (possibly related that the explanation behind stuttering is often a confused ''mess'').
G-sync and freesync are neat ''but'' the marketing and the typical complete lack of explanation is suspect.
Producers and reviewers seem very willing to imply
: vague "increases input lag dramatically" which is so vague that it's basically just ''wrong'', or
: "do you want to solve tearing ''without'' the framerate cap that vsync implies" and it's a pity that's pointing out the ''wrong'' issue about vsync,
: "G-Sync has better quality than FreeSync", whatever that means
Note that this also implies such a monitor's Hz rate is now a maximum, so it can show frames as soon as your GPU has them.
It seems to mean that the PC can instruct the monitor to start a new frame whenever it wants.
The monitor's refresh rate is now effectively the ''maximum''.
This in particular avoids the 'unnecessary further drop when frames come in slower than the monitor refresh rate'




Line 2,085: Line 2,211:


[[Visuals_DIY#Analog_video_notes]]
[[Visuals_DIY#Analog_video_notes]]


==Monitor mounts==
==Monitor mounts==

Latest revision as of 00:48, 29 April 2024

Few-element

Lighting

Nixie tubes



Eggcrate display

Mechanical

Mechanical counter

https://en.wikipedia.org/wiki/Mechanical_counter


Split-flap

https://en.wikipedia.org/wiki/Split-flap_display


Vane display

Flip-disc

https://en.wikipedia.org/wiki/Flip-disc_display


Other flipping types

LED segments

7-segment and others

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.
7-segment, 9-segment display, 14-segment, and 16-segment display. If meant for numbers will be a dot next to each (also common in general), if meant for time there will be a colon in one position.


These are really just separate lights that happen to be arranged in a useful shape.

Very typically LEDs (with a common cathode or anode), though similar ideas are sometimes implemented in other display types - notably the electromechanical one, and also sometimes VFD.


Even the simplest, 7-segment LED involves a bunch of connectors so are

  • often driven multiplexed, so only one of them is on at a time.
  • often done via a controller that handles that multiplexing for you


Seven segments are the minimal and classical case, good enough to display numbers and so e.g. times, but not really for characters.

More-than-7-segment displays are preferred for that.


https://en.wikipedia.org/wiki/Seven-segment_display

DIY

LCD character dislays

Character displays are basically those with predefined (and occasionally rewritable) fonts.


Classical interface

The more barebones interface is often a 16 pin line with a pinout like

  • Ground
  • Vcc
  • Contrast
usually there's a (trim)pot from Vcc, or a resistor if it's fixed


  • RS: Register Select (character or instruction)
in instruction mode, it receives commands like 'clear display', 'move cursor',
in character mode,
  • RW: Read/Write
tied to ground is write, which is usually the only thing you do
  • ENable / clk (for writing)
  • 8 data lines, but you can do most things over 4 of them


  • backlight Vcc
  • Backlight gnd


The minimal, write-only setup is:

  • tie RW to ground
  • connect RS, EN, D7, D6, D5, and D4 to digital outs


I2C and other

Matrix displays

(near-)monochrome

SSD1306

OLED, 128x64@4 colorsTemplate:Vierfy

https://cdn-shop.adafruit.com/datasheets/SSD1306.pdf

SH1107

OLED,

https://datasheetspdf.com/pdf-file/1481276/SINOWEALTH/SH1107/1

Small LCD/TFTs / OLEDs

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

Small as in order of an inch or two (because the controllers are designed for a limited resolution?(verify)).


💤 Note that, like with monitors, marketers really don't mind if you confuse LED-backlit LCD with OLED,

and some of the ebays and aliexpresses sellers of the world will happily 'accidentally' call any small screen OLED if it means they sell more.

This is further made more confusing by the fact that there are

  • few-color OLEDs (2 to 8 colors or so, great for high contrast but only high cotnrast),
  • high color OLEDs (65K),

...so you sometimes need to dig into the tech specs to see the difference between high color LCD and high color OLED.



When all pixels are off they give zero light pollution (unlike most LCDs) which might be nice in the dark. These seem to appear in smaller sizes than small LCDs, so are great as compact indicators.


Can it do video or not?

If it does speak e.g. MIPI it's basically just a monitor, probably capable of decent-speed updates, but also the things you can connect to will (on the scale of microcontroller to mini-PC) be moderately powerful, e.g. a raspberry.

But the list below don't connect PC video cables.

Still, they have their own controller, and can hold their pixel state one way or the other, but connect something more command-like - so you can update a moderate amount of pixels with via an interface that is much less speedy or complex.

You might get reasonable results over SPI / I2C for a lot of e.g. basic interfaces and guages. By the time you try to display video you have to think about your design more.

For a large part because amount of pixels to update times the rate of frames per second has to fit through the communication (...also the display's capabilities). There is a semi-standard parallel interface that might make video-speed things feasible. This interface is faster than the SPI/I2C option, though not always that much, depending on hardware details.


Even if the specs of the screen can do it in theory, you also have to have the video ready to send. If you're running it from an RP2040 or ESP32, don't expect to libav/ffmpeg.

Say, something like the TinyTV runs a 216x135 65Kcolor display from a from a RP2040.

Also note that such hardware won't be doing decoding and rescaling arbitrary video files. They will use specifically pre-converted video.


In your choices, also consider libraries. Things like TFT_eSPI has a compatibility list you will care about.



Interfaces

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.


ST7735

LCD, 132x162@16bits RGB


ST7789

LCD, 240x320@16bits RGB

https://www.waveshare.com/w/upload/a/ae/ST7789_Datasheet.pdf

SSD1331

OLED, 96x 64, 16bits RGB

https://cdn-shop.adafruit.com/datasheets/SSD1331_1.2.pdf


SSD1309

OLED, 128 x 64, single color?

https://www.hpinfotech.ro/SSD1309.pdf

SSD1351

OLED, 65K color

https://newhavendisplay.com/content/app_notes/SSD1351.pdf

HX8352C

LCD https://www.ramtex.dk/display-controller-driver/rgb/hx8352.htm


HX8357C

R61581

ILI9163

LCD, 162x132@16-bit RGB

http://www.hpinfotech.ro/ILI9163.pdf

ILI9341

https://cdn-shop.adafruit.com/datasheets/ILI9341.pdf

ILI9486

LCD, 480x320@16-bit RGB

https://www.hpinfotech.ro/ILI9486.pdf

ILI9488

LCD

https://www.hpinfotech.ro/ILI9488.pdf

PCF8833

LCD, 132×132 16-bit RGB

https://www.olimex.com/Products/Modules/LCD/MOD-LCD6610/resources/PCF8833.pdf

SEPS225

LCD

https://vfdclock.jimdofree.com/app/download/7279155568/SEPS225.pdf


RM68140

LCD

https://www.melt.com.ru/docs/RM68140_datasheet_V0.3_20120605.pdf

GC9A01

LCD, 65K colors, SPI

Seem to often be used on round displays(verify)

https://www.buydisplay.com/download/ic/GC9A01A.pdf

Epaper

SSD1619

https://cursedhardware.github.io/epd-driver-ic/SSD1619A.pdf


Many-element - TV and monitor notes (and a little film)

Backlit flat-panel displays

CCFL or LED backlight

https://nl.wikipedia.org/wiki/CCFL

Self-lit

OLED

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

While OLED is also a thing in lighting, OLED usually comes up in the context of OLED displays.

It is mainly contrasted with backlit displays (because it is hard to get those to block all light). OLEDs being off just emit no light at all. So the blacks are blacker, you could go brighter at the same time, There are some other technical details why they tend to look a little crisper.

Viewing angles are also better, roughly because the light source is closer to the surface.


OLED are organic LEDs, which in itself party just a practical production detail, and really just LEDs. (...though you can get fancy in the production process, e.g. pricy see-through displays are often OLED with substate trickery(verify))


PMOLED versus AMOLED makes no difference to the light emission, just to the way we access them (Passive Matrix, Active Matrix). AMOLED can can somwhat lower power, higher speed, and more options along that scale(verify), all of which makes them interesting for mobile uses. It also scales better to larger monitors.

POLED (and confusingly, pOLED is a trademark) uses a polymer instead of the glass, so is less likely to break but has other potential issues


QLED

On image persistence / burn-in

VFD

  • larger segments

    larger segments

  • dot matrix VFD

    dot matrix VFD

Vacuum Fluorescent Displays are vacuum tubes applied in a specific way - see Lightbulb_notes#VFDs for more details.



Some theory - on reproduction

Reproduction that flashes

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

Mechanical film projectors flash individual film frames while that film is being held entirely still, before advancing that film to the next (while no light is coming out) and repeating.

(see e.g. this and note that it moves so quickly that you see that the film is taken it happens so quickly that you don't even see it move. Separately, if you slow playback you can also see that it flashes twice before it advances the film - we'll get to why)

This requires a shutter, i.e. not letting through any light a moderate part of the time (specifically while it's advancing the film). We are counting on our eyes to sort of ignore that.


One significant design concept very relevant to this type of reproduction is the flicker fusion threshold, the "frequency at which intermittent light stimulus appears to be steady light" to our eyes because separately from actual image it's showing, it appearing smooth is, you know, nice.

Research shows that this varies somewhat with conditions, but in most conditions practical around showing people images, that's somewhere between 50Hz and 90Hz.


Since people are sensitive to flicker to varying degrees, and this can lead to eyestain and headaches, we aim towards the high end of that range whenever that is not hard to do.

In fact, we did so even with film. While film is 24fps and was initially shown at 24Hz flashes, movie projectors soon introduced two-blade and then three-blade shutters, showing each image two or three times before advancing, meaning that while they still only show 24 distinct images per second, they flash it twice or three times for a regular 48Hz or 72Hz flicker. No more detail, but a bunch less eyestrain.


As to what is actually being show, an arguably even more basic constraint is the rate of new images that we accept as fluid movement.

Anything under 10fps looks jerky and stilted
or at least like a choice.
western and eastern animations were rarely higher than 12, or 8 or 6 for the simpler/cheaper ones
around 20fps we start readily accepting it as continuous movement,
above 30 or 40fps it looks smooth,
and above that it keeps on looking a little better yet, with quickly diminishing returns



So why 24?

Film's 24 was not universal at the time, and has no strong significance then or now. It's just that when a standard was needed, the number 24 was a chosen balance between various aspects, like the fact that that's enough for fluid movement and relatively few scenes need higher, and the fact that film stock is expensive, and a standard for projection (adaptable or even multiple projectors would be too expensive for most cinemas).


The reason we still use 24fps today is more faceted, and doesn't really have a one-sentence answer.

But part of it is that making movies go faster is not always well received.

It seems that we associated 24fps to feels like movies, 50/60fps feels like shaky-cam home movies made by dad's camcorder (when those were still a thing) or sports broadcasts (which we did even though it reduced detail) with their tense, immediate, real-world associations. So higher, while technically better, was also associated with a specific aesthetic. It mat works well for action movies, yet less for others.

There is an argument that 24fps's sluggishness puts us more at ease, reminds us that it isn't real, seems associated with storytelling, a dreamlike state, memory recall.

Even if we can't put our finger on why, such senses persist.


CRT screens

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.


Also flashing

CRT monitors do something vaguely similar to movie projectors, in that they light up an image so-many times a second.


Where with film you light up the entire thing at once (maybe with some time with the shutter coming in and out, ignore that for now). a CRT light up one spot at a time - there is a beam constantly being dragged line by line across the screen -- look at slow motion footage like this.

The phosphor will have a softish onset and retain light for some while, and while slow motion tends to exaggerate that a little (looks like a single line), it's still visible for much less than 1/60th of a second.

The largest reason that these pulsing phosphors don't look like harsh blinking is that our persistence of vision (you could say our eyes framerate sucks, though actually this is a poor name for our eyes's actual mechanics), combined with the fact that it's relatively bright.


Flatscreens

✎ This article/section is a stub — some half-sorted notes, not necessarily checked, not necessarily correct. Feel free to ignore, or tell me about it.

Flatscreens do not reproduce by blinking things at us.

While in film, and in CRTs, the mechanism that lights up the screen is the is the same mechanism as the one that shows you the image, in LCD-style flatscreens, the image updates and the lighting are now different mechanisms.

Basically, there's one overall light behind the pixely part of the screen, and each screen pixel blocks light.


That global backlights tends to be lit fairly continuously. Sure there is variation in backlights, and some will still give you a little more eye strain than others.

CCFL backlight phosphors seem intentionally made to decay slowly, so even if the panel is a mere 100Hz, that CCFL ought to look look much less blinky than e.g. CRT at 100Hz.


LED backlights are often PWM'd at kHz speeds(verify), or current-limited(verify), which are both smoother.

If you take a high speed camera, you may still not see it flicker this part of the same slow motion video (note how the backlight appears constant even when the pixel update is crawling by) until you get really fast and specific.


So the difference between, say, a 60fps and 240fps monitor isn't in the lighting, it's how fast the light-blocking pixels in front of that constant backlight change. A 60fps monitor changes its pixels every 16ms (1/60 sec), a 240fps the latter every 4ms (1/240 sec). The light just stays on.

As such, while a cRT at 30Hz would look very blinky and be hard on the eyes, a flatscreen at 30fps updates looks choppy but not like a blinky eyestrain.



On updating pixels
On pixel response time and blur

Vsync

Adaptive sync

On perceiving

The framerate of our eyes

arguments for 60fps / 60Hz in gaming

On reaction time

On end-to-end latency

Tracking objects?

On intentional motion blur

On resolution

On contrast ratio / dynamic range

see also

Visuals_DIY#Analog_video_notes

Monitor mounts

VESA mounts

The sizes are often one of:

  • 7.5 cm x 7.5 cm (2.95 inches), 8kg max
  • 10 cm x 10 cm (3.94 inches), 12kg max
  • 20 cm x 20 cm (7.87 inches), 50kg+

...though there are smaller and larger variants, and also non-square ones.

Most products will have holes to fit more than one.

10cm was apparently the original, 7.5cm was added for smaller displays, though note that lightish displays could use either.


See also:

Monitor faults

Permanent lines on monitor

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