LCD pixels: what are chess-board pixel fill patterns called?

I have just recently bought a 4k HDR 55 inch TV (Vizio P55 F1). Here is photo of brightly lit pixels: (Source) The picture shows that the pixels are clearly squared and uniform. Often when I look at uniform color on the screen (think Playstation menus, but in real-life videos as well), I see that on various mid-bright spans of the same color the pixels lit in a chessboard pattern instead of uniform. On the last image the white letters seem more or less uniform, but the grey background definitely is not. I drew 2 green lines; the top one is going through the green subpixels that are brightly lit, and the bottom one is going through the green subpixels that are dim. The same goes for the blue lines, and for the red subpixels. When I output 4k content to a 4k screen, I expected it to be displayed pixel by pixel, but that is obviously not the case (or does the PS4 generate these patterns by itself?). I couldn't find anything about it on the internet because I was not able to find the 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. 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? Is uniformly lit TV better or worse? Is it generated at the source of the signal (PS4) or on the TV?

\$\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\$

\$\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\$

\$\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\$

\$\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\$

2 Answers 2

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.

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.

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

\$\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\$

\$\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\$

\$\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\$

\$\begingroup\$ This would help whoever stumbled on this question in the future, while searching for "chess-board patterns" at least \$\endgroup\$

Short Answer

"Subpixel antialiasing" may be the term you are looking for.

Longer Answer

Recognizing this is an old question, I'll be brief.

1. Dithering is usually used as a way to increase the apparent bit depth. This does not appear to be a dithering issue.
   • This display is a 10 bit display, meaning 10 bits per color channel.
     • This means 30 bits per pixel.
   • Typical PC would send 8 bit per R,G,B (24bit color), or the PS4 or a video source would often send a 4:2:2 signal (I don't work with PS4, so unsure if 4:2:2 or 4:4:4).
   • That said, the screen menu as shown is from?? Screen menus are typically "fast and dirty" so I wouldn't base a lot of opinions around how it's rendered. A test signal of known quality is better for such judgements.
2. Color subsampling (4:2:2) means the color information is at half the resolution of the luminance information.
   • This is commonly done to reduce data rates, as the human vision system processes color image information at about a third the resolution of the luminance information.
   • The artifacts from this are nominally invisible, but may be seen in some cases under high magnification.
3. Subpixel antialiasing is an "intentionally misaligned" independent use of the individual R,G,B subpixels to improve apparent resolution.
   • This is typically done in the rasterizer, before the signal is sent to the display.
   • but with "smart TVs". well, they have a ton of . Um. image "decoration" features, (which are often useless and unneeded and just there to "wow" customers on the sales floor, and no I'm not at all jaded, why do you ask?).
   • well, who knows what monkey business is afoot, but, there is a thread on subpixel problems with the P55-F1 specifically here: rtings.com - P55-F1 inferior pc usage with staggered sub pixels
4. Upscaling can create artifacts
   • where/when in the pipeline an image is scaled to the display's native resolution is also a factor here.
   • The review at rtings indicates some of the built in upscalings are "soft", and image scale transforms are always something of a compromise, with a number of different methods/algorithms.

4K Dirty Secret (a tangent)

I work in Hollywood. Many of the "4K" features are actually completed in 2K and then upscaled to 4K. By and large these upscalings are done using state-of-the-art technologies, and with shot by shot human review and adjustment.

But in studies conducted by ILM and others some years ago, it was found that bit depth and wider color gamut does much more for image fidelity than simply higher spatial resolution, especially for screens smaller than about five feet wide (when standing about eight feet away).

Once the screen pixel size is smaller than about one arc minute of visual angle, it is exceeding the theoretical resolving capability of the human vision system. This means that, assuming you are 8 feet away from the screen, a 2K, 60" diagonal screen is at this limit, thus smaller displays would have no real benefit to be 4K, assuming equivalent view distance.

Most people (20/20 vision) would be unable to tell the difference between a 60" 2K and 4K display, when standing 8 feet away, and all other things being equal. (Retailers turn on the image decoration nonsense like motion interpolation, and boosted contrast, to make people think there's a difference).

Where this can break down is with antialiasing and scaling artifacts, and such artifacts may be more noticeable to some people on a 2K screen. Someone with very good vision (20/12) might be able to tell the difference between a 2K and 4K display, as described, but only with content that was sensitive to that minuscule spatial difference, e.g. due to antialiasing or scaling artifacts.

The Point

When evaluating content on a 4K display, don't be surprised that there are things like scaling artifacts, or that content seems "softer" than you might expect.

Rule of Thumb (related to the above tangent)

2K is usually sufficient when the viewing distance is greater than about 1.6 times the diagonal screen size.

• When the view distance is greater than the diagonal screen size, it is increasingly likely that there will be no real benefit from using 4K.
• If the view distance is less than the diagonal screen size, then it is increasingly likely that 4K will provide a real benefit.

More Specific and Granular: The values below are based on standard 20/20 vision, in a typical indoor viewing environment, with "appropriate" or optimized content.

• Based on view distance:
  • multiply the viewing distance by 0.625 to find the diagonal screen size for 2K, where a smaller screen will most likely not benefit from 4K.
  • multiply the viewing distance by 1.25 to find the diagonal screen size for 4K, where a larger screen probably will benefit from 4K.
  • Between those two extremes, use case, environment, and typical content may be deciding factors.
  • multiply the diagonal screen size by 1.6 to determine the minimum idealized viewing distance for a 2K display. (2.6 for 20/12 vision)
  • multiply the diagonal screen size by 0.8 to determine the minimum idealized viewing distance for a 4K display. (1.3 for 20/12 vision)

  27" display, viewed 3½' away, 2k should be fine.
  27" display, viewed less than 2' away, 4k may be beneficial.

  2K: Here meaning 1920 x 1080
  4K: Here meaning 3840 x 2160