Am 27.12.2015 um 01:19 schrieb Mike Horvath:
> I'm rendering the attached scene on Windows, but the default
> assumed_gamma value of 1.0 seems too light. Switching it to 2.2 is much
> better. Is there something wrong with my scene, because as I understand
> it, you're really not supposed to mess with assumed_gamma.

And that's particularly true when rendering images that are supposed to
illustrate colour models.

As for how the image should properly look, that actually depends on the
colour model you're trying to illustrate: If the "value" parameter is
supposed to be linear, then it /must not appear/ linear. If the
parameter is instead supposed to be gamma-encoded, then approximate
linear /appearance/ is the right thing.

This is because when it comes to brightness, what /appears/ linear to
the eye actually isn't, and is actually close to a gamma of roughly 2.5.


Now while this would at first seem to imply that using assumed_gamma 2.2
would be the right thing to do if "value" is supposed to be
gamma-encoded, there is one thing to be aware of: Blending
/chromaticity/ in this mode is pretty messy. Whether it would give the
right results again would depend on the details of the colour model.


My suggestion would be to stick to assumed_gamma 1.0, and use POV-Ray
3.7.1's new colour_map/pigment_map "blend_mode" and "blend_gamma"
parameters for more control over the colour gradients. Use "blend_mode
1" for entirely linear interpolation, "blend_mode 2 blend_gamma 2.2" for
blending matching a gamma of 2.2, or "blend_mode 3 blend_gamma 2.2" to
get gamma 2.2 interpolation of brightness but gamma 1.0 interpolation of
chromaticity.

The defaults for these parameters are "blend_mode 0" (which performs
gamma-agnostic blending, effectively matching the assumed_gamma setting)
and "blend_gamma 2.5". Note that as opposed to most other gamma
settings, "srgb" is not a legal value for "blend_gamma".

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