4 ms·

"linear" is not a color space. Presumably they mean something like, sRGB but with linear gamma, but without understanding the design goals of this format it's h

"linear" is not a color space. Presumably they mean something like, sRGB but with linear gamma, but without understanding the design goals of this format it's hard to say what purpose the linear encoding serves.

lifthrasiir 4y ago
IIRC it is a late addition and only added because of people wanting some kind of color space guarantee. I don't think it was ever accurately specified what they do mean---presumably both share the sRGB color gamut and only differ by transfer functions, but it's a frequent misconception [1] that transfer functions can be parametrized with a single value, gamma, so I guess that's where the "linear" came from (implying gamma = 1.0). [1] The sRGB EOTF has a nominal gamma of 2.2 but it is actually a piecewise function with gamma varying from 1.0 to 2.4.
- esperent 4y ago
  > I guess that's where the "linear" came from (implying gamma = 1.0). "Linear" means the colors are stored in a state that means you can do linear transformations on them (basic math in other words) without loss. You can't do this with gamma corrected colors - for example as you say, the sRGB EOTF is a piecewise function so by definition it's not a linear transformation. So yes, when talking about "linear" colors, they still come from some gamut like sRGB or a larger HDR gamut. The linear part means they are safe for use in a renderer's internals.
- andreareina 4y ago
  I've implemented color-managed workflows so I should have suspected that of course sRGB would be like that, it has to.
  - lifthrasiir 4y ago
    Yeah, if you have the slightest experience with color space you would know that's a misconception, but I've seen enough cases where the 2.2 gamma is uniformly applied throughout the brightness curve...
- mananaysiempre 4y ago
  Compare how Netpbm declared[1] that colour images are BT.709 (HDTV) relatively late in its existence, and seemingly every other implementation ignores that and treats them as sRGB (same—or close enough—primaries, different transfer function). [1] https://netpbm.sourceforge.net/doc/ppm.html https://netpbm.sourceforge.net/doc/ppm.html
kaetemi 4y ago
Pretty much all modern 3D rendering is done in this color space that supposedly doesn't exist. Also, normal maps should be flagged as linear, since they should not get converted from the sRGB curve upon sampling.
- bscphil 4y ago
  Does that just mean that the color space is untagged / undefined? (That is in practice how I see a lot of games rendered - way oversaturated on my wide gamut screen.)
  - csande17 4y ago
    For normal maps, the correct color space is definitely "no color space", because the R/G/B channels are used to store a 3D vector and not an actual color. For video game graphics, the ideal color space is "looks good on the median user's television once we apply our gamma curve", which is not actually a real color space. It's more like a statistical distribution of color spaces.
    - bscphil 4y ago
      Normal maps, certainly. I was more confused by the parent's claim that this applied to "pretty much all modern 3D rendering". With video game graphics I'm surprised that PC games aren't handled differently. To the extent that TVs aren't garbage (huge assumption) traditional SDR TVs mostly target sRGB. But PC monitors can be almost anything, there are a ton of wide gamut (e.g. P3) screens out there, and saturated games can be retina-searing on them.
      - csande17 4y ago
        It'd probably be reasonable to say the output of a game's 3D renderer is sRGB or something, and to call the eye-searing colors on your P3 monitor a bug. But I think kaetemi's comment was talking about the intermediate calculations, which don't usually use sRGB. The "linear" color space used for those doesn't need to have a rigorous definition; even if there's no mathematically correct way to map a video-game-linear color to an sRGB color, the game company just hand-tweaks it until the game looks good.
iainmerrick 4y ago
Presumably they mean something like, sRGB but with linear gamma Yes, it’s exactly that, because: - almost all the time, the display is sRGB, so that’s your gamut; - almost all the time, you want to do your lighting and compositing in a linear space. - and sometimes your channels are normals or something, not colors at all, as others have noted. So it’s linear in the sRGB 0..255 gamut. It is a bit of a shame that most easy-to-use tools and workflows are limited to sRGB, so it’s really fiddly to support HDR displays and print.
- esperent 4y ago
  > almost all the time, the display is sRGB, so that’s your gamut; This is becoming less and less of a safe statement. On the one hand "yay HDR"! On the other hand, we're in for many years of weird bugs. For example recently I've been working on an app that I want to look good in HDR and I tried to share screenshots. Everything looked good to me. People on the other side were complaining about weird colors. Several hours of investigation later I realized that Windows was switching color spaces in my screenshots. Pressing the print screen button gave me a subtly different result than what I was actually seeing and of course I didn't spot it when emailing off the screen shots.
- jiggawatts 4y ago
  I'm reading this on an OLED display with about 90% of the gamut of Rec.2020. It's just a laptop, nothing special. Restricting colour to sRGB is going to be the CGA/EGA in a VGA world of the future.
  - iainmerrick 4y ago
    I hope you’re right!

lifthrasiir 4y ago

IIRC it is a late addition and only added because of people wanting some kind of color space guarantee. I don't think it was ever accurately specified what they do mean---presumably both share the sRGB color gamut and only differ by transfer functions, but it's a frequent misconception [1] that transfer functions can be parametrized with a single value, gamma, so I guess that's where the "linear" came from (implying gamma = 1.0). [1] The sRGB EOTF has a nominal gamma of 2.2 but it is actually a piecewise function with gamma varying from 1.0 to 2.4.

esperent 4y ago
> I guess that's where the "linear" came from (implying gamma = 1.0). "Linear" means the colors are stored in a state that means you can do linear transformations on them (basic math in other words) without loss. You can't do this with gamma corrected colors - for example as you say, the sRGB EOTF is a piecewise function so by definition it's not a linear transformation. So yes, when talking about "linear" colors, they still come from some gamut like sRGB or a larger HDR gamut. The linear part means they are safe for use in a renderer's internals.
andreareina 4y ago
I've implemented color-managed workflows so I should have suspected that of course sRGB would be like that, it has to.
- lifthrasiir 4y ago
  Yeah, if you have the slightest experience with color space you would know that's a misconception, but I've seen enough cases where the 2.2 gamma is uniformly applied throughout the brightness curve...
mananaysiempre 4y ago
Compare how Netpbm declared[1] that colour images are BT.709 (HDTV) relatively late in its existence, and seemingly every other implementation ignores that and treats them as sRGB (same—or close enough—primaries, different transfer function). [1] https://netpbm.sourceforge.net/doc/ppm.html https://netpbm.sourceforge.net/doc/ppm.html

kaetemi 4y ago

Pretty much all modern 3D rendering is done in this color space that supposedly doesn't exist. Also, normal maps should be flagged as linear, since they should not get converted from the sRGB curve upon sampling.

bscphil 4y ago
Does that just mean that the color space is untagged / undefined? (That is in practice how I see a lot of games rendered - way oversaturated on my wide gamut screen.)
- csande17 4y ago
  For normal maps, the correct color space is definitely "no color space", because the R/G/B channels are used to store a 3D vector and not an actual color. For video game graphics, the ideal color space is "looks good on the median user's television once we apply our gamma curve", which is not actually a real color space. It's more like a statistical distribution of color spaces.
  - bscphil 4y ago
    Normal maps, certainly. I was more confused by the parent's claim that this applied to "pretty much all modern 3D rendering". With video game graphics I'm surprised that PC games aren't handled differently. To the extent that TVs aren't garbage (huge assumption) traditional SDR TVs mostly target sRGB. But PC monitors can be almost anything, there are a ton of wide gamut (e.g. P3) screens out there, and saturated games can be retina-searing on them.
    - csande17 4y ago
      It'd probably be reasonable to say the output of a game's 3D renderer is sRGB or something, and to call the eye-searing colors on your P3 monitor a bug. But I think kaetemi's comment was talking about the intermediate calculations, which don't usually use sRGB. The "linear" color space used for those doesn't need to have a rigorous definition; even if there's no mathematically correct way to map a video-game-linear color to an sRGB color, the game company just hand-tweaks it until the game looks good.

iainmerrick 4y ago

Presumably they mean something like, sRGB but with linear gamma Yes, it’s exactly that, because: - almost all the time, the display is sRGB, so that’s your gamut; - almost all the time, you want to do your lighting and compositing in a linear space. - and sometimes your channels are normals or something, not colors at all, as others have noted. So it’s linear in the sRGB 0..255 gamut. It is a bit of a shame that most easy-to-use tools and workflows are limited to sRGB, so it’s really fiddly to support HDR displays and print.

esperent 4y ago
> almost all the time, the display is sRGB, so that’s your gamut; This is becoming less and less of a safe statement. On the one hand "yay HDR"! On the other hand, we're in for many years of weird bugs. For example recently I've been working on an app that I want to look good in HDR and I tried to share screenshots. Everything looked good to me. People on the other side were complaining about weird colors. Several hours of investigation later I realized that Windows was switching color spaces in my screenshots. Pressing the print screen button gave me a subtly different result than what I was actually seeing and of course I didn't spot it when emailing off the screen shots.
jiggawatts 4y ago
I'm reading this on an OLED display with about 90% of the gamut of Rec.2020. It's just a laptop, nothing special. Restricting colour to sRGB is going to be the CGA/EGA in a VGA world of the future.
- iainmerrick 4y ago
  I hope you’re right!