2 ms·

The problem is he is using the term "wider" which always refers to a change in the color range and not brightness. I agree gamut represents a 3D space.

jacobolus 7y ago
There are 2 things here: (1) The latest generation of displays (and presumably most displays in the future) use more colorful [spectrally spikier] “R”, “G”, and “B” primaries, with the result that they can display a wider range of chromaticities than an sRGB display. (2) If you make the brightness of a diffuse white reference less than the maximum which can be produced by your display then you have more headroom in each primary, and you can produce a much wider gamut of bright colors. The possible dark colors which can be produced don’t change. This makes it possible to accurately display e.g. very colorful flowers – with linear RGB coordinates of say (2.0, 0.0, 1.5) relative to (1.0, 1.0, 1.0) meaning diffuse white – which could not otherwise be shown if diffuse white were set to be the brightest combination of primaries for the display, because then the flower would necessarily get clipped to (1.0, 0.0, 1.0). [Sorry, this is a lot easier to see if you start looking at some graphics. It is not easy to clearly describe/understand with text alone.]
- rubatuga 7y ago
  To the first point, yes, I'm just being pedantic. But for the second point, how is that relevant? I'm not sure how this helps, because a) this has nothing to do with the display, i.e. we could modify an image to show the same effect on all displays, and b) gamut has not become wider at all.
  - jacobolus 7y ago
    It has to do with the display because recent displays can get much brighter than displays of the past. Instead of reaching a luminance of 80 of 100 nits, they can now reach 1000 or even 5000 nits. What this means is that it is now possible to set the target “diffuse white” luminance to be something like 200 nits, but then still be able to produce colors in which any (or all) of the primaries is 5x more intense than that. Until recently, it has been assumed that display white is (100%, 100%, 100%), whether the maximum display brightness happens to be 50 or 500 nits. But when displays can get to 1000 nits or beyond, that is no longer a tenable assumption. * * * If you have a conventional display (say a non-HDR TV or smartphone) you could still crank the display brightness all the way up but only show images or video where diffuse white was set to 20% of maximum (or whatever), and thereby achieve an expanded gamut for bright colors. But in practice few people if any ever did that. You can even do the same thing with a painting: if you make your painting overall darker than usual, place it on a dark gray wall, and then shine a very intense light on it, you can give your painting more dynamic range and a larger color gamut than you would otherwise be able to achieve with the same materials. This technique has been used to good effect by some (but relatively few) master painters, photographers, etc.
    - rubatuga 7y ago
      I'll try to summarize: if we are not physically getting a new combination of RGB cone stimulation ratios in our retinas, then the colour gamut has not become "wider". When compared to a SDR display, your HDR display that you mention above cannot display a RGB cone stimulation ratio that is not already achievable on the SDR display.

jacobolus 7y ago

There are 2 things here: (1) The latest generation of displays (and presumably most displays in the future) use more colorful [spectrally spikier] “R”, “G”, and “B” primaries, with the result that they can display a wider range of chromaticities than an sRGB display. (2) If you make the brightness of a diffuse white reference less than the maximum which can be produced by your display then you have more headroom in each primary, and you can produce a much wider gamut of bright colors. The possible dark colors which can be produced don’t change. This makes it possible to accurately display e.g. very colorful flowers – with linear RGB coordinates of say (2.0, 0.0, 1.5) relative to (1.0, 1.0, 1.0) meaning diffuse white – which could not otherwise be shown if diffuse white were set to be the brightest combination of primaries for the display, because then the flower would necessarily get clipped to (1.0, 0.0, 1.0). [Sorry, this is a lot easier to see if you start looking at some graphics. It is not easy to clearly describe/understand with text alone.]

rubatuga 7y ago
To the first point, yes, I'm just being pedantic. But for the second point, how is that relevant? I'm not sure how this helps, because a) this has nothing to do with the display, i.e. we could modify an image to show the same effect on all displays, and b) gamut has not become wider at all.
- jacobolus 7y ago
  It has to do with the display because recent displays can get much brighter than displays of the past. Instead of reaching a luminance of 80 of 100 nits, they can now reach 1000 or even 5000 nits. What this means is that it is now possible to set the target “diffuse white” luminance to be something like 200 nits, but then still be able to produce colors in which any (or all) of the primaries is 5x more intense than that. Until recently, it has been assumed that display white is (100%, 100%, 100%), whether the maximum display brightness happens to be 50 or 500 nits. But when displays can get to 1000 nits or beyond, that is no longer a tenable assumption. * * * If you have a conventional display (say a non-HDR TV or smartphone) you could still crank the display brightness all the way up but only show images or video where diffuse white was set to 20% of maximum (or whatever), and thereby achieve an expanded gamut for bright colors. But in practice few people if any ever did that. You can even do the same thing with a painting: if you make your painting overall darker than usual, place it on a dark gray wall, and then shine a very intense light on it, you can give your painting more dynamic range and a larger color gamut than you would otherwise be able to achieve with the same materials. This technique has been used to good effect by some (but relatively few) master painters, photographers, etc.
  - rubatuga 7y ago
    I'll try to summarize: if we are not physically getting a new combination of RGB cone stimulation ratios in our retinas, then the colour gamut has not become "wider". When compared to a SDR display, your HDR display that you mention above cannot display a RGB cone stimulation ratio that is not already achievable on the SDR display.