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I'm trying to figure out how many distinct colors are in p3 color gamut, can't seem to find the answer anywhere.

What I want to figure out is what is the minimum color depth required to fully support p3? Sounds like Apple iMac 5k from 2015 supports p3 but only has an 8 bit display, so I'm wondering how they can support p3 on a 8 bit display panel if the color gamut has billions of color

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  • question is closely related to this question and answer: photo.stackexchange.com/a/14274/19985 but dci-p3 is not shown in the image provided there. – meklarian Jul 6 '17 at 2:40
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    You also might be confusing the difference between 'supporting' and 'complying' with a technical standard. Here's an analogy that might be a little easier to grasp: If a 1920x1080 pixel Standard HD display can take a 4K signal and downsample it to HD and show the entire picture in the original aspect ratio it is said to "support" 4K video. For a display to be 4K "compliant", though, it must actually have a resolution of 3840x2160. – Michael C Jul 6 '17 at 3:47
  • Well, also, you could have, say, 8 total colors and still have them span the gamut.... – mattdm Jul 6 '17 at 19:35
  • A note on the closure vote, keep in mind that while DCI-P3 is a digital cinema gamut, the general question comes down to a broad understanding of how color gamuts work independent of the particular gamut and would still apply to photographic contexts as well. I can move it to video if we really want, but it seems like a fine fit here to me since the underlying question is still relevant to photography. – AJ Henderson♦ Jul 10 '17 at 16:34
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A Color Gamut refers to colors within a Color Space which is a representation of which colors exist within it and which ones are not.

It does not usually define a representation which is why there is not specific number of colord within it. sRGB for example use 3 chromacities which form a triangle within all possible colors. When one uses an 8-bit-per-component or 24 bits-per-pixel, it has 16,777,216 colors. When one uses 10-bits per color component or 30 bits-per-pixel, it has 1,073,741,824. TIFF files can use 32-bit values per component and so are able to represent even more colors with the sRGB color space.

So, there is no answer to your question but the screen determines how many colors can be displayed. Even so, it does not tell you which ones since the gamma affects spacing between colors and make it non linear. This means that two 8-bit monitors show the same number of colors within a color-space yet they may not show all the same colors. It gets worse if you calibrate your graphics card rather than the display. The LUTs loaded into the graphics card map an 8-bit input from the OS to the input that is supported by the monitor (usually 8 or 10-bits), in the worse case of an 8-bit monitor, after calibration it will not even use all possible colors which is why this often results in banding! It is immensely better to calibrate the monitor which can have 12 or 14-bit Hardware LUTs, so they can map a full 8-bit input to the bit-depth of the display without loss of the number of possible colors shown.

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  • If gamut does not define the actual colors and instead just defines the space (triangle) within which all the colors should be defined -- then what defines or describes this triangle? Sorry I'm probably using all the wrong terms here. As I understand any and all colors can be defined with RGB value, so an 8 bit color depth has 16M colors possible and 10 bit ~ billion colors. If RGB is what's defining the colors then what is the color gamut describing? – newbie Jul 6 '17 at 8:06
  • @newbie - A color space is a continuous space and can be defined by different means. sRGB is defined as all blending of its three base chromacities representing the chosen pure Red, pure Green and pure Blue. AdobeRGB is defined in the same way but with different base chromaticies. One can use any precision you want, including floating point numbers to interpolate between base colors. – Itai Jul 6 '17 at 13:24
  • @newbie - to clarify a bit further, you might find this article informative. The actual color of 100% red, 100% green and 100% blue differ in different color spaces and are defined as different placements on the spectrum of visible colors that the average human can see. A display manufacturer can choose their own colors for 100% red, 100% green and 100% blue (as well as their pixel layout) such that it enables displaying their own triangle on the same human vision chart. – AJ Henderson♦ Jul 6 '17 at 14:13
  • The percentage that they overlap defines the % of coverage the monitor gives, so 126% sRGB coverage means that a monitor can cover all of sRGB plus 26% more of the visible spectrum than sRGB can cover. – AJ Henderson♦ Jul 6 '17 at 14:13
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Photo engineers strive to make images that are faithful reproductions of reality. The current state of the art is to fracture an image of a vista via red, green and blue filters. These are the light primary colors. Computer screens, phone screens, and giant movie screens present these three images and our eye/brain combination discerns a color image. The DCI-P3 is a digital color gamut designed to mimic photographic film. This standard is based on a projector equipped with a xenon light source. The idea is to equip the projector with red, green, and blue filters adjusted to reduce “cross talk” that results should the filter be a mismatch to the light source. No computer or phone or TV screen can accurately match such a system but they can come close.

As to the number of color that results, this is a function of bit depth. 8 bit color = 256 shades per each of the three primary colors. 16 bit color delivers 4,096 levels of intensity per each primary color.

While the applied signals are as advertised, I find it doubtful that the actual illumined picture elements respond linearly. In other words, I strongly doubt that any system actually delivers the number of color advertised.

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