6 ms·

sRGB and its transfer function are inseparable, by definition. IEC 61966-2-1:1999 defines sRGB as a color space with its particular non-linear transfer function

by pornel 4y ago

sRGB and its transfer function are inseparable, by definition. IEC 61966-2-1:1999 defines sRGB as a color space with its particular non-linear transfer function. When you linearize sRGB you create a new not-sRGB-anymore color space that happens to have a compatible white point and RGB primaries.

esperent 4y ago
> a new not-sRGB-anymore color space that happens to have a compatible white point and RGB primaries. Do you know if this new color space has an official name? I work with it basically everyday via the three.js renderer internals and mostly see it refered to as simply "linear", but if more specificity is needed usually I see "linear sRGB". I think that's common even if it's not correct. However as HDR color spaces take over from sRGB I expect it'll become more important to have a correct name for this color space. I have searched for one previously but haven't been able to come up with anything better than "linear sRGB".
- Espressosaurus 4y ago
  When you take sRGB and apply an inverse gamma curve to it you end up in linear light space. Is that what you're referring to? The choice of the inverse gamma curve you're using is a choice with no single answer depending on how you intend to map that linear light onto...whatever it is you're doing. The obvious one is to use the nominal gamma of 2.2. That may or may not make sense depending on your display technology and what you're doing.
- akvadrako 4y ago
  scRGB with the 16-bit encoding.
- dahart 4y ago
  “Linear” is in practice the official name. The only additional specificity you can have is to give the scalar conversion factor from your linear colors into physical units like lumens or candela or watts per solid angle or surface area. What linear means is that you’re working in a scaled set of physical units. The scale factor is the only thing missing. You might not ever need the physical scale factor, it doesn’t generally matter. You probably didn’t set your light or color intensities in three.js using physical units in the first place, and even if you did you might be simply scaling the values until things look right. We usually scale the inputs and outputs manually anyway, so the absolute scale of the intermediate linear color space in CG is frequently irrelevant. HDR is mostly referring to whether your values are conceptually [0..1] or [0..infinity]. Sometimes people are also referring to how many bits get used per color channel. (But note that the R is HDR is referring to ‘range’ and not to ‘resolution’.) 8 bit color values that represent [0..1] are unambiguously LDR, while 32 bits per channel color values that represent [0..inf] are unambiguously HDR. If you use 16 bit colors and your range is [0..3] to allow for headroom and glare effects, it’s not really considered HDR, but it’s not exactly LDR either. It mostly only makes sense to work with HDR values in a linear color space, but it’s not strictly or by definition necessary. “Linear sRGB” gets used sometimes, and what it means is that a color was converted from sRGB into linear. So the space is actually just linear. It’s useful to know if a color came from sRGB sometimes, because there’s less worry about going back into sRGB if you know it came from sRGB originally, and it helps you understand something about the scale and brightness of your linear values. If you have linear values and don’t know where they came from, you have no point of reference, and no idea if a value of 0.1 means invisible black, blinding white, or just middle gray. But unless I scale the linear colors, I do know a linear sRGB value of 0.1 is a dark gray that’s visible, because I know that the range of color is approximately [0..1] because it came from sRGB.
  - mncharity 4y ago
    > You probably didn’t set your light or color intensities in three.js using physical units in the first place, Nod... unless you're using a color space, like Jzazbz, with an absolute (not relative) transfer function. Application context then motivates the nit pick. So a Jzazbz HDR of [0..10k], might get a daylight 1k nits picked for diffuse (non-highlight) white. Thus I appreciate it when color libraries provide a distinct Absolute XYZ D65 data type.
    - dahart 4y ago
      This is a good point! Jzazbz is a good example of the (somewhat rare) application of perceptual response functions in high dynamic range. I’d be curious to hear what reasons you have to use Jzazbz. The color space seems best at scenarios where you need to compute HDR color differences. Most people don’t need that, but some advanced users like you do. Worth noting in this context that Jzazbz is non-linear, and even though it’s HDR, it still requires conversion to a linear space in order to blend colors physically. I want to elaborate just slightly on what I meant. In CG, like in real photography, the photographer almost always sets some combination of their exposure, aperture size, and/or white balance values manually, regardless of how well they’re controlling inputs and color spaces. As a simple example, I can always dim the lights by a factor of 2 power, and also either expose for twice as long, or open my shutter by one f-stop. When I dim lights by half and expose by double, then nothing about the image changes. Even if you know the physical luminosity of your lights, the overall process (usually) still cancels scale factors and at the end reduces to an arbitrary scaling that essentially sets the output white and output black to the brightest and darkest colors I want to show, respectively. With real film, there are additional arbitrary scaling values like the film development process, and lighting conditions when viewing. With digital, the display’s scaling is frequently unknown, and thus arbitrary; you might use 1k nits for your daylight diffuse, but that’s not what your monitor actually shows you. There are legit use-cases for wanting absolute physical values in the intermediate stages, and using a “linear” color space for blending is, in a way, emulating exactly that desire but still with an arbitrary scale because the input brightness and/or output brightness are being tuned by hand.
Asooka 4y ago
No, it's still sRGB. Usually it's referred to as "linear sRGB" or "linear Rec. 709" to make the distinction clear. The latter uses the same XY coordinates for its R G and B channels, but a slightly different transfer function.
- dahart 4y ago
  You have misunderstood what some people mean when they say “linear sRGB”. That is a term that means linear color space with the gamut of what used to be an sRGB color. It is no longer an sRGB color, but it’s safer to transfer back into sRGB later, there are fewer worries about whether your colors will be clipped to the wrong bounds. The term “linear sRGB” helps you understand the provenance of your inputs, it does not mean your color values are in the sRGB color space.

by pornel 4y ago

esperent 4y ago

> a new not-sRGB-anymore color space that happens to have a compatible white point and RGB primaries. Do you know if this new color space has an official name? I work with it basically everyday via the three.js renderer internals and mostly see it refered to as simply "linear", but if more specificity is needed usually I see "linear sRGB". I think that's common even if it's not correct. However as HDR color spaces take over from sRGB I expect it'll become more important to have a correct name for this color space. I have searched for one previously but haven't been able to come up with anything better than "linear sRGB".

Espressosaurus 4y ago
When you take sRGB and apply an inverse gamma curve to it you end up in linear light space. Is that what you're referring to? The choice of the inverse gamma curve you're using is a choice with no single answer depending on how you intend to map that linear light onto...whatever it is you're doing. The obvious one is to use the nominal gamma of 2.2. That may or may not make sense depending on your display technology and what you're doing.
akvadrako 4y ago
scRGB with the 16-bit encoding.
dahart 4y ago
“Linear” is in practice the official name. The only additional specificity you can have is to give the scalar conversion factor from your linear colors into physical units like lumens or candela or watts per solid angle or surface area. What linear means is that you’re working in a scaled set of physical units. The scale factor is the only thing missing. You might not ever need the physical scale factor, it doesn’t generally matter. You probably didn’t set your light or color intensities in three.js using physical units in the first place, and even if you did you might be simply scaling the values until things look right. We usually scale the inputs and outputs manually anyway, so the absolute scale of the intermediate linear color space in CG is frequently irrelevant. HDR is mostly referring to whether your values are conceptually [0..1] or [0..infinity]. Sometimes people are also referring to how many bits get used per color channel. (But note that the R is HDR is referring to ‘range’ and not to ‘resolution’.) 8 bit color values that represent [0..1] are unambiguously LDR, while 32 bits per channel color values that represent [0..inf] are unambiguously HDR. If you use 16 bit colors and your range is [0..3] to allow for headroom and glare effects, it’s not really considered HDR, but it’s not exactly LDR either. It mostly only makes sense to work with HDR values in a linear color space, but it’s not strictly or by definition necessary. “Linear sRGB” gets used sometimes, and what it means is that a color was converted from sRGB into linear. So the space is actually just linear. It’s useful to know if a color came from sRGB sometimes, because there’s less worry about going back into sRGB if you know it came from sRGB originally, and it helps you understand something about the scale and brightness of your linear values. If you have linear values and don’t know where they came from, you have no point of reference, and no idea if a value of 0.1 means invisible black, blinding white, or just middle gray. But unless I scale the linear colors, I do know a linear sRGB value of 0.1 is a dark gray that’s visible, because I know that the range of color is approximately [0..1] because it came from sRGB.
- mncharity 4y ago
  > You probably didn’t set your light or color intensities in three.js using physical units in the first place, Nod... unless you're using a color space, like Jzazbz, with an absolute (not relative) transfer function. Application context then motivates the nit pick. So a Jzazbz HDR of [0..10k], might get a daylight 1k nits picked for diffuse (non-highlight) white. Thus I appreciate it when color libraries provide a distinct Absolute XYZ D65 data type.
  - dahart 4y ago
    This is a good point! Jzazbz is a good example of the (somewhat rare) application of perceptual response functions in high dynamic range. I’d be curious to hear what reasons you have to use Jzazbz. The color space seems best at scenarios where you need to compute HDR color differences. Most people don’t need that, but some advanced users like you do. Worth noting in this context that Jzazbz is non-linear, and even though it’s HDR, it still requires conversion to a linear space in order to blend colors physically. I want to elaborate just slightly on what I meant. In CG, like in real photography, the photographer almost always sets some combination of their exposure, aperture size, and/or white balance values manually, regardless of how well they’re controlling inputs and color spaces. As a simple example, I can always dim the lights by a factor of 2 power, and also either expose for twice as long, or open my shutter by one f-stop. When I dim lights by half and expose by double, then nothing about the image changes. Even if you know the physical luminosity of your lights, the overall process (usually) still cancels scale factors and at the end reduces to an arbitrary scaling that essentially sets the output white and output black to the brightest and darkest colors I want to show, respectively. With real film, there are additional arbitrary scaling values like the film development process, and lighting conditions when viewing. With digital, the display’s scaling is frequently unknown, and thus arbitrary; you might use 1k nits for your daylight diffuse, but that’s not what your monitor actually shows you. There are legit use-cases for wanting absolute physical values in the intermediate stages, and using a “linear” color space for blending is, in a way, emulating exactly that desire but still with an arbitrary scale because the input brightness and/or output brightness are being tuned by hand.

Asooka 4y ago

No, it's still sRGB. Usually it's referred to as "linear sRGB" or "linear Rec. 709" to make the distinction clear. The latter uses the same XY coordinates for its R G and B channels, but a slightly different transfer function.

dahart 4y ago
You have misunderstood what some people mean when they say “linear sRGB”. That is a term that means linear color space with the gamut of what used to be an sRGB color. It is no longer an sRGB color, but it’s safer to transfer back into sRGB later, there are fewer worries about whether your colors will be clipped to the wrong bounds. The term “linear sRGB” helps you understand the provenance of your inputs, it does not mean your color values are in the sRGB color space.