Am 27.12.2016 um 09:21 schrieb Kenneth:

> I decided to run your test scene with assumed_gamma 1.0 instead of 2.2, and
> noticed something about your use of 'rgb' in the light_source. I changed it to
> srgb (which I've started doing in all my v3.7xx scenes, to be 'color-consistent'
> with all the other srgb colors I use), and noticed that the scene gets
> *brighter.* It's an interesting (and unexpected) effect-- unexpected because,
> when substituting srgb colors for rgb (under assumed_gamma 1.0), it usually
> causes the lighting/colors to be be somewhat *darker* (as expected, due to the
> gamma shift of the color components away from linear.) But in this case, the
> result is the opposite-- it's brighter!
> 
> I assume this is because the light's intensity is greater than 1.0; but I don't
> quite understand why. Is it a natural consequence of the srgb 'gamma curve',
> affecting color components above 1.0? (Or maybe above a particular
> 'intermediate' value between 0.0 and 1.0?)

You can think of "srgb C" as (roughly) equivalent to "rgb pow(C,2.2)",
i.e. very roughly squaring the colour value. As you may be aware, the
square of a (positive) value below 1 is an even smaller value, while the
square of a value above 1 is an even larger value.

The sRGB "transfer function" (that's the official technical term) is
indeed designed in such a way that it is neutral for values of 0 and 1,
while adjusting any values in between. Since it was designed for
situations where colours are clipped to this range, no special handling
is provided for larger values, and the effect is reversed there.


BTW, in the nominal region (between 0 and 1) the largest absolute effect
of gamma adjustment is roughly around an sRGB value of 0.5 (a linear
value of about 0.24), while the largest relative effect is near black.

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