[Bf-committers] Updating Colour Configurations

Brecht Van Lommel brechtvanlommel at pandora.be
Tue Nov 10 23:46:35 CET 2015

I doubt GPU rendering is a problem, but I have no idea what the word
"role" means in this context and what "implementing an XYZ role"

On Mon, Nov 9, 2015 at 2:30 AM, Troy Sobotka <troy.sobotka at gmail.com> wrote:
> On Sun, Nov 8, 2015 at 5:17 PM Brecht Van Lommel <brechtvanlommel at pandora.be>
> wrote:
>> On Sun, Nov 8, 2015 at 6:42 PM, Troy Sobotka <troy.sobotka at gmail.com>
>> wrote:
>> > I have only peeked at the Cycles GPU path code, but it doesn't seem like
>> > there is a terrible level of chromaticity based hacks in place? I only
>> saw
>> > the sRGB transfer curve hard coded? Perhaps there is a bit in the SSS
>> code?
>> > (Being code that makes assumptions about the RGB primaries and rolls them
>> > through XYZ such as the hard-coded color temperature node.)
>> Cycles inputs and outputs are mostly scene linear colors and it
>> doesn't need to know much about that color space, but there are a
>> couple exceptions.
>> The simple changes would be in the wavelength, blackbody and sky
>> texture nodes, which make some assumptions about using Rec.709 scene
>> linear. An extra transformation between different scene linear spaces
>> should be enough to solve that. The Blender API just needs to expose
>> information about the scene linear color space so that Cycles can
>> construct those transformations, which I guess are just 3x3 matrices.
> I chatted with Antony at length on this and I am reasonably sure that there
> is a quick and easy method to solve many of the issues in Blender while we
> wait for OCIO to implement chromaticity information, which is hopefully
> sooner rather than later.
> The basic solution is to implement an XYZ role. This is reasonably simple
> to carve out, and smaller studios / artists with unique configurations
> would simply have to take care to provide the XYZ role and assert that the
> white points are aligned.
> The colour selectors and such could also leverage this role.
> Do you think it is feasible to leverage the role against Cycles for these
> sorts of cases or does the GPU path provide a problem?
> With respect,
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