> clipka <ano### [at] anonymousorg> wrote:
>> 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.)
>
> Interesting. Do the default values now reflect assumed gamma 1.0 then or do we
> still have to tweak them for assumed gamma 1.0?
>

The diffuse should be OK, maybe reduce ambient. For the rest, it should 
be correct.

something in that range, in the global_settings block.

It's relatively simple: assumed_gamma 1 = correct calculations and 
minimal tweaking. assumed_gamma <> 1 = incorrect calculations and LOTS 
of tweakings.

Post a reply to this message