Am 22.12.2016 um 05:08 schrieb Dave Blandston:
> clipka <ano### [at] anonymousorg> wrote:
>> The second image shows essentially the same scene with `assumed_gamma
>> 2.2`, with the diffuse settings (`diffuse` and `brilliance`) adjusted to
>> get exactly the same diffuse effect out of the different colour math.
> 
> Please forgive my ignorance, but does that mean the default settings for diffuse
> and brilliance are meant to give the most visually appealing results with an
> assumed_gamma of 2.2?

It is more complicated than that.

> I never really gave assumed_gamma much thought. I just noticed that setting it
> to 1.0 produced a washed-out result so I picked 2.2 and never thought about it
> again.

Here are a few facts:

- The brilliance default of 1 fits /perfectly/ with `assumed_gamma 1.0`,
because the developers back then naively implemented a formula that was
designed for linear colours. The whole `brilliance` mechanism is an
awfully hackish thing, and it so happens that it can be used to achieve
the same proper look with other gamma settings (as far as diffuse goes),
so my guess is that it was introduced specifically for the purpose of
fixing the look of diffuse objects, in times when people probably didn't
even know what gamma handling was.

- The diffuse default of 0.7 was presumably introduced in times when bad
gamma handling was the norm, and it can be assumed that it was set in
such a way as to get pleasing results in /that/ environment. In a gamma
1.0 scenario, that would correspond to a setting of about 0.45.


- As Warp demonstrated not long ago, one main reason (besides trying to
use gamma-pre-corrected colours without the "srgb" keyword) for the
washed-out look in gamma 1.0 mode seems to be the "ambient" default:
That setting, too, was quite certainly designed for a gamma of about
2.2, and in a gamma 1.0 scenario that would correspond to an ambient
setting of 0.006 (though that number is difficult to nail down, as
ambient is always added to colours, and adding colours without proper
gamma handling greatly distorts them, particularly if their absolute
value is rather small.)


- Without proper gamma handling, there is stuff that you just simply
/cannot/ get right simultaneously (as demontrated with these images); so
you may need a /lot/ of tweaking to get /somewhat/ close to a realistic
look, and you'll have to do this /over and over again/ for virtually
each and every scene, as you'll need to fine-tune yor materials for the
given lighting conditions and vice versa. On the other hand, with gamma
1.0 all it takes is some experience, and once you get your materials
right you can re-use them quite easily in virtually every lighting
condition. (Also, with proper gamma handling the number of knobs to
tweak is smaller, since you never need to fiddle with any of those
unrealistic hacks like brilliance, reflection exponent, or light source
fade_power values other than 2.0.)

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