AgX-Step3: Refactor OCIO config to be CIE XYZ I-E based #110913
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Reference: blender/blender#110913
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Delete Branch ":AgX-Step3"
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This is step 3 of the AgX implementation, as discussed in the original AgX PR
EDIT: Forgot to mention this also involved in renaming of the XYZ space, as mentioned by the comment
XYZ Scaling
to the more accurateBradford
0ff4ef2b8c@blender-bot build
@ -97,4 +124,2 @@
- !<BuiltinTransform> {style: "UTILITY - ACES-AP1_to_CIE-XYZ-D65_BFD", direction: inverse}
- !<ColorSpace>
name: XYZ
This is a significant change that breaks forward compatibility, but it is not mentioned in the PR description.
@ -62,2 +63,4 @@
colorspaces:
- !<ColorSpace>
name: Linear CIE-XYZ I-E
Slightly shorter name:
Linear CIE-XYZ E
@ -64,0 +69,4 @@
equalitygroup:
bitdepth: 32f
description: |
1931 CIE XYZ Standard with assumed I-E white point
Standard -> standard
I-E -> illuminant E
@ -64,0 +73,4 @@
isdata: false
- !<ColorSpace>
name: Linear CIE-XYZ I-D65
Slightly shorter name:
Linear CIE-XYZ D65
As can be seen from the aliases, it's not common to have this
I-
prefix and not self explanatory anyway.@ -64,0 +79,4 @@
equalitygroup:
bitdepth: 32f
description: |
1931 CIE XYZ with adapted I-D65 white point
I-D65 -> illuminant D65, here we can actually use the full word
@ -64,0 +82,4 @@
1931 CIE XYZ with adapted I-D65 white point
isdata: false
from_scene_reference: !<FileTransform> {src: xyz_E_to_D65.spimtx, interpolation: linear}
to_scene_reference: !<FileTransform> {src: xyz_D65_to_E.spimtx, interpolation: linear}
Is it necessary to provide transforms in two directions?
I wonder if that might actually affect performance negatively, if perhaps in this case OpenColorIO can no longer cancel out the transforms.
Comments are adressed.
@blender-bot build
LGTM.
I've created a patch for 3.6 to keep forward compatibility as per our policy: #110924
Sorry I'm a bit late to this. Didn't realize it would get merged so quickly.
A tiny nit: rather than
Linear CIE-XYZ I-E
orLinear CIE-XYZ E
it can just beLinear CIE XYZ
. X=Y=Z is already defined to be E by the standard, so mentioning it in the name seems redundant to me. E.g. we don't call sRGB "sRGB D65", etc. It does make sense in the D65 XYZ variant, though, since that deviates from actual CIE XYZ.(I also wondered briefly if we should drop the
Linear
prefix as well, for similar reasons. But thinking a bit more, it probably makes sense to have a general linear/non-linear distinction for the spaces, and we're already using theLinear
prefix for that anyway.)We can add an alias if needed, but on the interface I'd rather stick to a fully disambiguated naming. I do not think it is great to require people to know standards by heart to know which illuminant is used. When you see "Linear CIE-XYZ E" you know for sure what it is. If you see "Linear CIE-XYZ" you'll be like "holap, lemme double check my knowledge of standard".
I could see that. But to expand on my perspective:
To me it's more that CIE XYZ doesn't have a white point in the traditional sense. In RGB color spaces, for example, the white point plays double-duty:
In CIE XYZ, on the other hand, X=Y=Z -> illuminant E is purely about defining the coordinate system colorimetrically, and has none of the perceptual implications usually associated with specifying a white point. It's a bit of a subtle distinction, but in my mind at least it means that CIE XYZ does not have a white point as such—it's just purely a colorimetric coordinate system. And that's also what makes it useful as the foundation upon which other color spaces define their white points.
(XYZ D65, on the other hand, does introduce a white point into XYZ. Making it no longer CIE XYZ per se.)
In any case, I don't feel strongly about it. So I'm fine leaving it as-is. It just feels a little misleading to me, I guess, in terms of what CIE XYZ is.
From that argument I slightly prefer just "Linear CIE-XYZ", but don't feel very strongly about it either way.