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I have just recently bought a 4k hdr 55 inch tv (Vizio P55 F1). Here is photo of brightly lit pixels from https://www.rtings.com/tv/reviews/vizio/p-series-2018

Fully lit square unifor pixels from rtings https://i.rtings.com/images/reviews/tv/vizio/p-series-2018/p-series-2018-pixels-large.jpg

Picture shows that pixels are clearly squared and uniform

Often when I look at uniform color on the screen (think Playstation menus, but in the real-life videos as well), I see that on various mid-bright spans of same color pixels lit in a chessboard pattern instead of uniform.

image of a PS4 menu https://i.imgur.com/iUekscp.jpg image of a PS4 menu closeup https://i.imgur.com/jTGzBjd.jpg

On the last image white letters seem more or less uniform, but grey background is definitely not. I draw 2 green lines - top one is going through green subpixels that are brightly lit, and bottom one is going through green subpixels that are dim. Same goes with blue lines, and same goes with red subpixels.

When I get a 4k screen and output a 4k content to it, I expected it to be displayed pixel by pixel, but that is obviously not the case (or is it PS4 generate this patterns by itself?).

I couldn't find anything about it on the internet because I was not able to find proper name for this effect.

I must add that I just recently saw a tv that doesn't have this effect, but I don't remember the model.

My question is - what is the name of this approach, so I can read about it and understand the reason behind it?

Bonus questions - what is the rationale under it? Is uniformly lit tv is better or worse? Is it generated on the source of signal (ps4) or on the tv?

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  • \$\begingroup\$ I doubt that the menu is 4k content, so likely your TV is upscaling and dithering it. Check your TVs settings for a game mode or so, almost all TVs these days play fun things to get a better image, especially when HDR is needed and they can't get it with just the colour resolution of a single pixel. \$\endgroup\$ – PlasmaHH Oct 17 '18 at 8:14
  • \$\begingroup\$ Bayer filtering? \$\endgroup\$ – filo Oct 17 '18 at 8:17
  • \$\begingroup\$ While the output sent to the screen is UHD, it's entirely possible that the content being displayed is an image file that is less than UHD resolution (maybe 1080p), so gets scaled up in the frame buffer of the PS-2 before being sent to the screen. \$\endgroup\$ – Tom Carpenter Oct 17 '18 at 9:27
  • \$\begingroup\$ Also this doesn't seem to be about electronic design - its not a bad question at all and should probably should be migrated to a different stack, though not sure which is the best fit. \$\endgroup\$ – Tom Carpenter Oct 17 '18 at 9:28
  • \$\begingroup\$ @PlasmaHH, I have explicitly switched PS4 from 4k to 2k and back, effect is the same. I haven't tried to wire it through non-hdr HDMI input (special low-lag gaming SDR input), and I haven't tried to disable HDR directly, will try tomorrow. I have also tested this on a Ultra HD Grand Tour episode from Prime Video built into TV. After it gathers its wits, it shows true 4k, and tv explicitly said so, and I already found good scenes to distinguish 2k from 4k. Also did the same with Youtube 4k video. I doubt it is upscaling, I thought these are "fun things" ,wanted to find the name for them. \$\endgroup\$ – YanTS Oct 17 '18 at 9:52
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This is due to the panel control driver, and you probably won't find much info about it because this is the secret sauce of each manufacturer.

This is definitely the TV doing that and not the playstation.

The reason behind it is probably, that the driver for each pixel is able to light only at certain amount of brightness, if it is for example a 4 bit per pixel ratio, you will have 16 level of brightness by pixel, for each color.

Now 16 levels per pixel is not a lot, it would give 4'096 different possible colors in total.

But now, if you set different levels per pixel rows, you can drastically increase the amount of possible colors, as anyway from your eye you won't be able to spot single pixels and will only see the average of it.

With only controlling this effect on two rows, you go from 4 bits to 2x 4 bits, this will give you 16'777'216 different possible color, while using the exact same amount of data as before.

So you go from 4'096 color levels to 16+ millions, while driving the panel with the same amount of data.

It is also probably cheaper to drive individual pixels in 4 bits than 8 bits.

Since 4k panel have a large amount of pixel, this technique is likely used to reduce the bandwidth needed to drive the panel as well as the driver cost, as you need 2x less data for the same result.

Take the 4 bits per pixel as an example, I do not know how many bit per pixel is being used, but 4 is a likely possibility.


EDIT

Since the TV is given at 1 billion + color, it is possible individual pixels to be driven in 5 bits, with two rows that would give approximately 1 billion colors.

Or that each pixel is driven in 4 bits and that effect is applied on 3 rows, which is more likely as it usually a power of 2.


EDIT 2:

Followed on the comments, it seems to be called "color dithering".

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  • \$\begingroup\$ Hey, Damien. Your answer is useful, and I want to accept it, but it does not answer the main question - the name of the approach I observed. After searching more and more, I came to understanding that this approach is indeed "spatial dithering", though it does not give a good tag to search for. \$\endgroup\$ – YanTS Dec 7 '18 at 5:24
  • \$\begingroup\$ Try to search for color dithering 6bits,it shows up quite a bit off article about it. lifewire.com/lcd-displays-and-bit-color-depth-833083 \$\endgroup\$ – Damien Dec 8 '18 at 7:23
  • \$\begingroup\$ I still want to mark you anser as accepted, as soon as you add word "dithering" to the answer itself, meaning that is the name of the behavior I observe. \$\endgroup\$ – YanTS Dec 11 '18 at 2:11
  • \$\begingroup\$ This would help whoever stumbled on this question in the future, while searching for "chess-board patterns" at least \$\endgroup\$ – YanTS Dec 11 '18 at 2:11
  • \$\begingroup\$ Done @YanTS :). \$\endgroup\$ – Damien Dec 11 '18 at 3:37

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