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"Kenneth" <kdw### [at] gmail com> wrote:
>
> The various results using different assumed_gamma values:
> --- With assumed_gamma 1.0:
> 1) using srgb: eval_pigment = <0.522522,0.522522,0.522522> // correct
> 2) using rgb: eval_pigment = <0.750000,0.750000,0.750000> // correct
> --- With assumed_gamma 2.2:
> // 1) using srgb: eval_pigment = <0.744501,0.744501,0.744501> // ??
> // 2) using rgb: eval_pigment = <0.750000,0.750000,0.750000>
> --- with assumed_gamma srgb:
> // 1) using srgb: eval_pigment = <0.750000,0.750000,0.750000>
> // 2) using rgb: eval_pigment = <0.750000,0.750000,0.750000>
>
> Under assumed_gamma 1.0, the evaluated values are correct. But under
> assumed_gamma 2.2, the result with srgb is *slightly* off from the original
> value. I have no idea why. (I would have thought that those two values would be
> MUCH different, like under assumed_gamma 1.0).
The srgb keyword always returns a color that *looks* the same across all
assumed_gamma settings. To take your example, srgb 0.75 will *look* the same
whether your scene uses assumed_gamma 1, assumed_gamma 2.2, or assumed_gamma
srgb. But this implies that, internally, it will evaluate to different rgb
values depending on the assumed_gamma setting.
When you use assumed_gamma srgb, the scene's nonlinearity aligns with the color
definition, which is why rgb and srgb return the same value. And since sRGB is
close to gamma 2.2, rgb and srgb return close, but not identical, values under
assumed_gamma 2.2.
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