Display types: Difference between revisions
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= | =Few-element= | ||
== | ==Lighting== | ||
===Nixie tubes=== | |||
[[Image:Nixie2.gif|thumb|right|]] | |||
<!-- | <!-- | ||
Nixie tubes were some of the earliest outputs of computers | |||
They have been a inefficient solution since the transistor or so. | |||
But they're still pretty. | |||
[[Lightbulb_notes#Nixie_tubes]] | |||
--> | |||
<br style="clear:both"> | |||
===Eggcrate display=== | |||
<!-- | |||
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 | |||
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. | |||
--> | --> | ||
=== | ==Mechanical== | ||
===Mechanical counter=== | |||
https://en.wikipedia.org/wiki/Mechanical_counter | |||
===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. | |||
They are | They are entirely mechanical, and only need to be moderately precise -- well, assuming they only need ~36 or so characters. | ||
https://www.youtube.com/watch?v=UAQJJAQSg_g | |||
--> | --> | ||
https:// | https://en.wikipedia.org/wiki/Split-flap_display | ||
<br style="clear:both"/> | |||
===Vane display=== | |||
===Flip-disc=== | |||
https://en.wikipedia.org/wiki/Flip-disc_display | |||
===Other flipping types=== | |||
<!-- | |||
--> | |||
==LED segments== | |||
===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.]] | |||
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<!-- | |||
: 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 | |||
--> | |||
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==== | |||
<!-- | |||
Basically the above wrapped in a controller you can address via I2C or SPI (and usually they then speak that older parallel interface) | |||
Sometimes these are entirely separate ones bolted onto the classical interface. | |||
For DIY, you may prefer these just because it's less wiring hassle. | |||
--> | |||
===Matrix displays=== | |||
===(near-)monochrome=== | |||
====SSD1306==== | |||
OLED, 128x64@4 colors{{vierfy}} | |||
https://cdn-shop.adafruit.com/datasheets/SSD1306.pdf | |||
====SH1107==== | |||
OLED, | |||
https://datasheetspdf.com/pdf-file/1481276/SINOWEALTH/SH1107/1 | |||
===Small LCD/TFTs / OLEDs=== | |||
{{stub}} | |||
Small as in order of an inch or two (because the controllers are designed for a limited resolution?{{verify}}). | |||
{{zzz|Note that, like with monitors, marketers really don't mind if you confuse 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. | |||
}} | |||
<!-- | |||
[[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)]] | |||
--> | |||
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 {{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. | |||
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. | |||
====Interfaces==== | |||
{{stub}} | |||
<!-- | |||
* 4-line SPI | |||
* 3-line SPI ([[half duplex]], basically) | |||
* I2C | |||
* 6800-series parallel | |||
* 8080-series parallel interface | |||
-- | 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}} | |||
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 | |||
--> | |||
=== | ====ST7735==== | ||
LCD, 132x162@16bits RGB | |||
<!-- | |||
* SPI interface (or parallel) | |||
* 396 source line (so 132*RGB) and 162 gate line | |||
* display data RAM of 132 x 162 x 18 bits | |||
* 2.7~3.3V {{verify}} | |||
Boards that expose SPI will have roughly: | |||
: GND: power supply | |||
: VCC: 3.3V-5.0V | |||
: SCL: SPI clock line | |||
: SDA: SPI data line | |||
: RES: reset | |||
: D/C: data/command selection | |||
: CS: chip Selection interface | |||
: BLK: backlight control (often can be left floating, presumably pulled up/down) | |||
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 | ||
: | |||
Arduino libraries | |||
* https://github.com/adafruit/Adafruit-ST7735-Library | |||
* 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. | |||
'''ucg notes''' | |||
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 | |||
--> | |||
====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 | |||
==== | |||
<!-- | <!-- | ||
240(RGB)x480, 16-bit | |||
--> | |||
https://www.ramtex.dk/display-controller-driver/rgb/hx8352.htm | |||
====HX8357C==== | |||
====R61581==== | |||
<!-- | |||
240x320 | |||
--> | --> | ||
=== | ====ILI9163==== | ||
LCD, 162x132@16-bit RGB | |||
http://www.hpinfotech.ro/ILI9163.pdf | |||
=== | ====ILI9341==== | ||
<!-- | |||
240RGBx320, 16-bit | |||
--> | |||
https://cdn-shop.adafruit.com/datasheets/ILI9341.pdf | |||
==== | ====ILI9486==== | ||
LCD, 480x320@16-bit RGB | |||
https://www.hpinfotech.ro/ILI9486.pdf | |||
====ILI9488==== | |||
LCD | |||
<!-- | |||
320(RGB) x 480 | |||
--> | |||
https://www.hpinfotech.ro/ILI9488.pdf | |||
====PCF8833==== | |||
LCD, 132×132 16-bit RGB | |||
https:// | 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 | |||
<!-- | <!-- | ||
320 RGB x 480 | |||
--> | --> | ||
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 | |||
[[Category:Computer]] | |||
[[Category:Hardware]] | |||
=Many-element - TV and monitor notes (and a little film)= | |||
==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. | |||
There are roughly two parts of such monitors you can care about: How the backlight works, and how the pixels work. | |||
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 | |||
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), | |||
: 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 | |||
TFT, UFB, TFD, STN | |||
--> | |||
===CCFL or LED backlight=== | |||
<!-- | |||
Both refer to a global backlight. | |||
It's only things like OLED and QLED that do without. | |||
CCFLs, Cold-Cathode Fluorescnt Lamps, are a variant of [[fluorescent lighting]] that (surprise) runs a lot colder than some other designs. | |||
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. | |||
LED backlights are often either | |||
* [[PWM]]'d at kHz speeds{{verify}}, | |||
* current-limited{{verify}}, which are both smoother. | |||
--> | --> | ||
https://nl.wikipedia.org/wiki/CCFL | |||
==Self-lit== | |||
===OLED=== | |||
{{stub}} | |||
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. | |||
{{comment|(...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 | |||
<!-- | |||
'''Confusion''' | |||
"Isn't LED screen the same as OLED?" | |||
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". | |||
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. | |||
"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}} | |||
--> | |||
=== | ===QLED=== | ||
<!-- | |||
It's quantum, so it's buzzword compatible. How is it quantum? Who knows! | |||
It may surprise you that this is LCD-style, not OLED-style, | |||
but is brighter than most LCD style, | |||
they're still working on details like decent contrast. | |||
Quantum Dot LCD https://en.wikipedia.org/wiki/Quantum_dot_display | |||
--> | |||
==On image persistence / burn-in== | |||
<!-- | <!-- | ||
CRTs continuously illuminating the same pixels would somewhat-literally cook their phosphors a little, | |||
-- | leading to fairly-literal image burn-in. | ||
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. | |||
'''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. | |||
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''. | |||
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. | |||
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. | |||
A screensaver with white, or strong moving colors, or noise, may help. | |||
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). | |||
https://en.wikipedia.org/wiki/Image_persistence | |||
http://www.jscreenfix.com/ | |||
http://gribble.org/lcdfix/ | |||
{{search|statictv screensaver}} | |||
--> | --> | ||
==VFD== | |||
<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. | |||
<br style="clear:both"/> | |||
= | <!-- | ||
==Capabilities== | |||
== | ===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. | |||
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) | |||
'' | 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. | ||
===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. | |||
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. | |||
However, the millisecond measure is nontrivial. The direct meaning of the number has been slaughtered primarily by number-boast-happy PR departments. | |||
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 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. | |||
8ms is fairly usual these days. Pricier screens will do 4ms or even 2ms, which is nicer for gaming. | |||
===Video noise=== | |||
The | ===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. | |||
===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. | |||
300 cd/m2 is fairly usual. | |||
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. | |||
===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. | |||
==Convenience== | |||
===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. | |||
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. | |||
The angle, either from a perpendicular line (e.g. 75°) or as a total angle (e.g. 150°). | |||
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. | |||
===Reflectivity=== | |||
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 seems that many glare filters will reduce your color fidelity, though. | |||
--> | --> | ||
==Some theory - on reproduction== | |||
====Reproduction that flashes==== | |||
{{stub}} | {{stub}} | ||
'''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. [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. | |||
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. | |||
<!-- | |||
'''when more both is and isn't better''' | |||
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. | |||
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''). | |||
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}} | |||
'''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 {{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. | |||
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. | |||
<!-- | |||
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. | |||
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. | |||
'''How do pixels get sent?''' | |||
--> | |||
====Flatscreens==== | |||
{{stub}} | |||
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 [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. | 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. | 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 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. | |||
<!-- | <!-- | ||
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[[Visuals_DIY#Analog_video_notes]] | [[Visuals_DIY#Analog_video_notes]] | ||
==Monitor mounts== | ==Monitor mounts== |
Revision as of 17:42, 15 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
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
Small as in order of an inch or two (because the controllers are designed for a limited resolution?(verify)).
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
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
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
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
-
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
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
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
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
What Vsync adds
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: