Display types: Difference between revisions

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{{zzz|Note that, like with monitors, marketers really don't mind if you confuse backlit LCD with OLED,
{{zzz|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'  
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.
call any small screen OLED if it means they sell more.
Line 401: Line 401:
https://www.melt.com.ru/docs/RM68140_datasheet_V0.3_20120605.pdf
https://www.melt.com.ru/docs/RM68140_datasheet_V0.3_20120605.pdf


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


LCD, 65K colors, SPI
LCD, 65K colors, SPI
Seem to often be used on round displays{{verify}}


https://www.buydisplay.com/download/ic/GC9A01A.pdf
https://www.buydisplay.com/download/ic/GC9A01A.pdf
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[[Category:Hardware]]
[[Category:Hardware]]


=TV and monitor notes (and a little film)=
===Epaper===
 
====SSD1619====
 
https://cursedhardware.github.io/epd-driver-ic/SSD1619A.pdf
 
<!--
<!--
==Capabilities==
====UC8151====


===Resolution===
https://www.orientdisplay.com/wp-content/uploads/2022/09/UC8151C.pdf
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.
=Many-element - TV and monitor notes (and a little film)=
==Backlit flat-panel displays==
<!--


===Refresh===
We may call them LCD, but that was an early generation
Refresh rates as they existed in CRT monitors do not directly apply; there is no line scanning going on anymore.
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.


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.
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




However, the millisecond measure is nontrivial. The direct meaning of the number has been slaughtered primarily by number-boast-happy PR departments.
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


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


TFT, UFB, TFD, STN


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.
===CCFL or LED backlight===


<!--
Both refer to a global backlight.
It's only things like OLED and QLED that do without.


===Video noise===


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


===Contrast===
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.
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===
They are also high voltage devices.
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.


LED backlights are often either
* [[PWM]]'d at kHz speeds{{verify}},
* current-limited{{verify}}, which are both smoother.


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


==Self-lit==


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


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


===Viewing angle===
It is mainly contrasted with backlit displays (because it is hard to get those to block all light).
The viewing angle is a slightly magical figure. It's probably well defined in a test, but its meaning is a little elusive.
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.


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


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




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


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


-->
==On reproduction==


====Reproduction that flashes====
<!--


{{stub}}
'''Confusion'''


'''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.


{{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)}}
"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".


This requires a shutter, i.e. not letting through any light a moderate part of the time (specifically while it's advancing the film).
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.
We are counting on our eyes to sort of ignore that.
The cost-benefit for people without a bunch of disposable income isn't really there.


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.


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


"I heard al phones use OLED now?"


Since people are sensitive to flicker, some more than than others, and this can lead to eyestain and headaches,
Fancier, pricier ones do, yes.
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.
Cheaper ones do not, because the display alone might cost on the order of a hundred bucks.{{verify}}






An arguably even more basic constraint to moving pictures is the point at which rate of images we accept animation as '''fluid movement'''.
: 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.


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


Early movies on film were approximately 24fps, some faster, various slower.
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).


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


The reason we ''still'' use 24fps it now is more varied and doesn't really have a one-sentence answer.
they're still working on details like decent contrast.


But part of it is that making movies go faster is only sometimes 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.
Quantum Dot LCD  https://en.wikipedia.org/wiki/Quantum_dot_display
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.
-->


==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.




'''when more is and isn't better'''
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.


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


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


At the same time, a lot of seems like a learned association that will blur and may go away over time.
'''OLED''' seems to as well, though it's subtler.




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'').
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.


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


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


Unplugging power (/ turning it off) for hours (or days, or sometimes even seconds) may help, and may not.


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


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


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).
with a CRT there is a constantly-flowing beam of electrons lighting whatever phosphor it hits,
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,
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
https://en.wikipedia.org/wiki/Image_persistence
(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.


http://www.jscreenfix.com/


<!--
http://gribble.org/lcdfix/
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.
{{search|statictv screensaver}}


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.
-->


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


And yes, after working behind one of those faster-rate monitors and moving to a 60Hz monitor would be ''really'' noticeable.
[[Vacuum Fluorescent Display]]s are vacuum tubes applied in a specific way - see [[Lightbulb_notes#VFDs]] for more details.
Because even when we accept it as smooth enough, it still blinked, and we still perceive it as such.


<br style="clear:both"/>


'''How do pixels get sent?'''




<!--
==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.


====Flatscreens====
For:
{{stub}}
* 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)


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,
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.
in LCD-style flatscreens (including QLED) they are separate - there is a global CCFL or LED backlight, and the pixels are light ''blockers''.
{{comment|(In QLED there are the same again, though with some new footnotes)}}


===Refresh===
Refresh rates as they existed in CRT monitors do not directly apply; there is no line scanning going on anymore.


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,
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.  
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.
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.
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.
However, the millisecond measure is nontrivial. The direct meaning of the number has been slaughtered primarily by number-boast-happy PR departments.
A 60fps monitor changes its pixels every 16ms (1/60 sec), a 240fps the latter every 4ms (1/240 sec).


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.


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 in one way, it's more about the fps, but at the same time, the Hz rating usually ''is'' its physical fps.
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.


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


Note also that dimming a PWM'd backlight screen will effectively change the flicker a little.
8ms is fairly usual these days. Pricier screens will do 4ms or even 2ms, which is nicer for gaming.
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.


There are another few reasons why both can flicker a little more than that suggests, but only mildly so.
===Video noise===




===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.


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.
===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.


But it's often not specced very well - so whether any particular monitor is better or worse for eyestrain is essentially not specced.
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.


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


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
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.
==Convenience==


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


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''.
The angle, either from a perpendicular line (e.g. 75°) or as a total angle (e.g. 150°).
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).  
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.


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


'''How are CRT monitors different from CRT TVs?'''


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.
-->
==Some theory - on reproduction==


Early game consoles/computers just generated a TV signal, so that you could use the TV you already had.
====Reproduction that flashes====


After that, CRT monitors started out as adapted CRT TVs.
{{stub}}
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.
'''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.
Or rather, resolution-refresh combinations. Detecting and dealing that is a topic in and of itself.


(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)


Yet at the CRT level, they were driven much the same way -
This requires a shutter, i.e. not letting through ''any'' light a moderate part of the time (specifically while it's advancing the film).
synchronization timing to let the monitor know when and how fast to sweep the beams around,
We are counting on our eyes to sort of ignore that.
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,
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.
''most'' of that 16ms is spent moving values onto the wire and onto the screen.


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.


'''How are flatscreens different from CRTs?'''
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.


The physical means of display is completely different.


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.


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


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.


Regardless of how many colors,
actually just transferring that many individual values will take some time.




The hsync and vsync signals still exist,
'''So why 24?'''
though LCDs are often a little more forgiving, apparently keeping a short memory and allowing some syncing [https://youtu.be/muuhgrige5Q?t=425]


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).




Does a monitor have a framebuffer and then update everything at once?
The reason we ''still'' use 24fps ''today'' is more faceted, and doesn't really have a one-sentence answer.
It ''could'' be designed that way if there was a point, but there rarely is.
It would only make things more expensive for no reason.


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


When the only thing we are required to do is to finish drawing one image before the next starts,  
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.
then we can spend most of that time sending pixels,  
So higher, while technically better, was also associated with a specific aesthetic. It mat works well for action movies, yet less for others.
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.


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.


And when we were using VGA on flatscreens, that was what we were doing.
Even if we can't put our finger on why, such senses persist.


Panels even tend to update a line at a time.
<!--
'''when more both is and isn't better'''


Why?
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.
: 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])).


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.




Scanout itself basically refers to the readout and transfer of the framebuffer on the PC side,
At the same time, a lot of seems like a learned association that will blur and may go away over time.


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


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 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.


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}}


'''Would it 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.
'''Also flashing'''


Transferring millions of numbers takes time, meaning that to update everything at once you need to wait until you've stored all of it,
CRT monitors do something ''vaguely'' similar to movie projectors, in that they light up an image so-many times a second.
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).


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 per-line tradeoff described above makes much more sense for multiple reasons.
The phosphor will have a softish onset and retain light for some while,
Do things ''more or less'' live,
and while slow motion tends to exaggerate that a little (looks like a single line),  
but do it roughly one line at a time - we can do it ''sooner'',  
it's still visible for much less than 1/60th of a second.
it requires less storage,
we can do it over dozens to hundreds of lines to the actual panel.


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]]).


'''If you can address lines at a time, you could you do partial updates this way?'''
Most CRT ''monitors'', unlike TVs, can be told to refresh at different rates.


Yes. And that exists.
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.
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
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.


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,


Some browser/office things are mostly static - except when you scroll.
'''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.


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


When in particular the earliest gaming consoles were made, RAM was expensive.
That global backlights tends to be lit ''fairly'' continuously.
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.
Sure there is variation in backlights, and some will still give you a little more eye strain than others.
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'.


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.


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.


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.


======Screen tearing and vsync======


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.


'''When to draw'''
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.


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,
<!--
but if that bears no relation to when the graphics card sends new frames,
'''Footnotes to backlight'''
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.


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. 


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.
On regular screens the dimming is usually fixed, for laptop screens it may do so based on battery status as well as ambient light.


There are another few reasons why both can flicker a little more than that suggests, but only mildly so.


One of the simplest ways around that is '''double buffering''':
: 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:
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.
Whenever you are done drawing, you tell the graphics card to flip to the other one.


But it's often not specced very well - so whether any particular monitor is better or worse for eyestrain is essentially not specced.


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


-->


Roughly speaking,
: 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",


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


<!--


In the latter case, you will often see part of two different images. They will now always be ''completely drawn'' images,
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)}}
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.
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
This is arguably a feature, because if this happens regularly (and it would), it happens at different positions all the time,
to notice this - see e.g. [https://youtu.be/3BJU2drrtCM?t=52].
which is less visible than if they are very near each other (it would seem to slowly move).


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.


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


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).


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''.
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).}}


----




'''Does that mean it's updating pixels while you're watching rather than all at once?'''
'''How are CRT monitors different from CRT TVs?'''


Yes.
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.


Due to the framerate alone it's still fast enough that you wouldn't notice.
On color TV there were some extra details, but a good deal worked the same way.
As that slow mo video linked above points out, you don't even notice that your phone screen is probably updating sideways.


Early game consoles/computers just generated a TV signal, so that you could use the TV you already had.


Note that while in VGA, the pixel update is fixed by the PC,  
After that, CRT monitors started out as adapted CRT TVs.
in the digital era we are a little less tied.  
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.


In theory, we could send the new image ''much'' faster than the speed at which the monitor can update itself,
We also grew an increasing amount of resolutions that the monitor should be capable of displaying.
but in practice, you don't really gain anything by doing so.
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.


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


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.


'''How are flatscreens different from CRTs?'''


The physical means of display is completely different.


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.


---
Regardless of how many colors,
actually just transferring that many individual values will take some time.


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.
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]


(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


Does a monitor have a framebuffer and then update everything at once?
It ''could'' be designed that way if there was a point, but there rarely is.
It would only make things more expensive for no reason.




'''Are flatscreen TVs any different?'''
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.


Depends.


Frequently yes, because a lot are sold with some extra Fancy Processing&tm;, like interpolation in resolution and/or time,
And when we were using VGA on flatscreens, that was what we were doing.
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))


Panels even tend to update a line at a time.


And that tends to add a few to a few dozen milliseconds.
Why?
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.
: 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])).


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




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


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


'''Are there other ways of updating?'''


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


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.




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


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


No and yes.
Transferring millions of numbers takes time, meaning that to update everything at once you need to wait until you've stored all of it,
and you've gained nothing in terms of speed.


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


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


-->


=====On pixel response time and blur=====
The per-line tradeoff described above makes much more sense for multiple reasons.
<!--
Do things ''more or less'' live,
So, each pixel cannot change its state instantly. It's on the order of a few milliseconds.
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.


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.




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.
'''If you can address lines at a time, you could you do partial updates this way?'''
: this matters more to high contrast (argument for BwB, WbW)
: but most of most images isn't high contrast (argument for GtG)


Yes. And that exists.
But it turns out there are few cases where this tradeoff is actually useful.


One way to work around this, on a technical level, is higher framerate.
And now you also need some way to keep track of what parts (not) to update,
''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.
which tends to mean either a very simple UI, or an extra framebuffer


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.
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,  


Some browser/office things are mostly static - except when you scroll.


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


-->


====What Vsync adds====


<!--




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).


''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.
''' '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'.


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.
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 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.


======Screen tearing and vsync======




There are two common ingredients to the solution:
'''When to draw'''


* vsync in the sense of waiting until we are between frames
So, the graphics card has the job of sending 'start new frame' and the stream of pixels.
:: 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
You ''could'' just draw into the framebuffer whenever,
:: means we have two framebuffers: one that is currently being sent to the screen, and one we are currently drawing to
but if that bears no relation to when the graphics card sends new frames,
:: and at some time we tell the GPU to switch between the two
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.




Double buffering with vsync off means ''switch as soon as we're done drawing''.
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.
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.


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),
One of the simplest ways around that is '''double buffering''':
then this discontinuity is ''usually'' barely visible, because either the frames tend to look very similar,
: have one image that the graphics card is currently showing,  
or it happens at random positions on the screen, or both.
: have one hidden next one that you are drawing to
: tell the graphics card to switch to the other when you are done


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




So the most proper choice is vsync on ''and'' '''double buffering'''. With this combination:
How do we keep it in step? Varies, actually, due to some other practical details.  
* we have two framebuffers that we flip between
* we flip them when the video card is between frames


Roughly speaking,
: 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",




'''vsync is also rate limiting. And in a integer division way.'''
Another benefit to vsync on is that we don't try to render faster than necessary.
60Hz screen? We will be sending out 60 images per second.


...well, ''up to'' 60. Because we wait until a new frame, that means a very regular schedule that we have no immediate control over.  
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.


At 60Hz, you need to finish a new frame within 16.67ms (1 second / 60).
If the timing of drawing and monitor draw is unrelated, this will be at an unpredictable position.
Did you take 16.8ms? Then you missed it, and the previous frame will stay on screen for another 16.67ms.
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).




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.


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).


So assuming things are a little late, do we get locked into 30fps instead?


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,




And even that varies on the way the API works.
'''Does that mean it's updating pixels while you're watching rather than all at once?'''
: 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}}


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.


(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,
Note that while in VGA, the pixel update is fixed by the PC,  
meaning immediate framrerates that are integer divisions of the native rate.
in the digital era we are a little less tied.  


To games, vsync is sort of bad, in that if you ''structurally'' take more than 16.8ms aiming for 60Hz,
In theory, we could send the new image ''much'' faster than the speed at which the monitor can update itself,
you will be running at a solid 30fps, not something inbetween 30 and 60.
but in practice, you don't really gain anything by doing so.
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.






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


Notes:
Yes. Except it's over multiple ''milliseconds''.
: vsync this is not the same mechanism as double buffering, but it is certainly related


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.








'''Related things'''
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]].


---


Screen capture, relevant in these game-streaming days, may be affected by vsync in the same way.
There would be little point to keeping a coping of an entire screen, since we're reading from a framebuffer just as before.  
It's basically a ''third'' party looking at the same frame data, so another thing to ''independently'' have such tearing and/or slowdown issues.
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




====Vsync====


Intuitively, vsync tells the GPU to wait until refresh.
'''Are flatscreen TVs any different?'''


Depends.


This is slightly imprecise, in a way that matters later.  
Frequently yes, because a lot are sold with some extra Fancy Processing&tm;, like interpolation in resolution and/or time,
What it's really doing is telling the GPU to flip buffers until the next refresh.
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))




In theory, we could still be rendering multiples more frames,
And that tends to add a few to a few dozen milliseconds.
and only putting out some to the monitor.
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.


But there is typically no good reason to do so,  
so enabling vsync usually comes with reducing the render rate to the refresh rate.
So if they having a "gaming mode", that usually means "disable that processing".




Similarly, disabling vsync does not ''necessarily'' uncap your framerate, because developers may
have other reasons to throttle frames.




'''Are there other ways of updating?'''


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


'''Vsync when the frames come too fast''' is a fairly easy decision,
At the same time, they may figure out that you're staring at static text,  
because we only tell the GPU to go no faster than the screen's refresh rate.
so they may refresh the framebuffer and/or screen ''much'' less often.


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.
'''Is OLED different?'''


No and yes.


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


'''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.


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


Say, if we have a 60Hz screen (16.7ms interval) and 50fps rendering (20ms interval),
There are various metrics, like
 
* GtG (Gray To Gray)
* if you start a new frame render after the previous one got displayed, you will miss every second frame, and be displaying at 30fps.
* BwB (black-white-black)  
* WbW (white-black-white)


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




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.
: this matters more to high contrast (argument for BwB, WbW)
: but most of most images isn't high contrast (argument for GtG)


You can work this out on paper, but it comes down to that it will run at an integer divisor of the framerate.


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.
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.


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


-->


====Vsync====


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


What vsync adds




'''Adaptive VSync'''
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).


If the fps is higher than the refresh, VSync is enabled,
''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.
if the fps is lower than the monitor refresh, it's disabled.


This avoids


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


'''NVidia Fast Sync''' / '''AMD Enhanced Sync'''
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)


Adaptive VSync that adds triple buffering to pick.


Useful when you have more than enough GPU power.
It's lowest latency to get things on screen, but can look incorrect.






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.


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.
* 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


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).
Double buffering with vsync off means ''switch as soon as we're done drawing''.
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.
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).
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.
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.


'''Could it get any more complex?'''


Oh, absolutely!
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.'''
 
Another benefit to vsync on is that we don't try to render faster than necessary.
60Hz screen? We will be sending out 60 images per second.
 
...well, ''up to'' 60. Because we wait until a new frame, that means a very regular schedule that we have no immediate control over.


'''I didn-'''
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.


...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.  
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.
 
 
So assuming things are a little late, do we get locked into 30fps instead?
 
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,
 
 
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}}
 
 
 
(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,
meaning immediate framrerates that are integer divisions of the native rate.
 
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.
 
 
 
 
Notes:
: vsync this is not the same mechanism as double buffering, but it is certainly related
 
 
 
 
 
 
'''Related things'''
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]].
 
 
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.
 
 
 
 
 
====Vsync====
 
Intuitively, vsync tells the GPU to wait until refresh.
 
 
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.
 
 
In theory, we could still be rendering multiples more frames,
and only putting out some to the monitor.
 
But there is typically no good reason to do so,
so enabling vsync usually comes with reducing the render rate to the refresh rate.
 
 
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.
 
 
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.
 
* 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.
 
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.
 
 
 
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.
 
 
 
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].
Games try to avoid this, but [some people take that as a challenge].


 
 
 
 
-->
-->
 
 
====Adaptive sync====
====Adaptive sync====
<!--
<!--
 
{{stub}}
Where most monitors keep a regular schedule (and set it themselves).
 
 
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.
 
 
Nvidia G-sync and AMD Freesync treats frame length them as varying.
 
 
Note that doing this requires both a GPU and monitor that support this.  
 
 
Basically, the GPU sending a new frame will make the monitor start updating it as it comes in,
Which so far is a gamer niche.  
rather than on the next planned interval.
 
 
And the two mentioned buzzwords are not compatible with each other,
 
but for some reason, most articles don't get much further than  
Manufacturer marketing as well as reviewers seem very willing to imply
"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'').
: 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
G-sync and freesync are neat ''but'' the marketing and the typical complete lack of explanation is suspect.
 
 
A more honest way of putting it might be
Producers and reviewers seem very willing to imply
"when frames come in slower than the monitor's maximum,
: vague "increases input lag dramatically" which is so vague that it's basically just ''wrong'', or
we go to the actual render rate, without tearing"
: "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
...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).
 
 
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.
There's absolutely value to that, but dramatic? Not very.
 
 
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''.
 
 
Note that doing this requires both a GPU and monitor that support this.  
 
 
This in particular avoids the 'unnecessary further drop when frames come in slower than the monitor refresh rate'
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'
 




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[[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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