Question on texture input gamma

[beenyweenies]

From the manual:

Gamma - the bitmap data is gamma corrected with the specified gamma value specified by the Texture input gamma attribute, so V-Ray will need to remove this gamma correction for rendering;
sRGB - the bitmap data is in the sRGB color space, so V-Ray will need to convert it to linear physical space for rendering.

My question is twofold - when does one normally use the "Gamma" option? From the description, I'm mostly picturing a texture file with incorrect gamma baked in (like the old Mac OS 1.8 gamma or something). Also, does the sRGB option apply to any and all file formats, as long they have an sRGB profile?

Thanks!

[Morbid Angel]

No this isn't quite correct. Its simple when your typical camera takes a picture and saves it as jpg as final result either right away or after raw conversion it embeds a curve into it. Usually its a gamma 2.2 curve.

When you load that texture into maya and use it for diffuse color lets say, in the linear workflow environment where everything is treated with gamma 1.0 and only during rendering its displayed with gamma 2.2 what happens is that texture already has a 2.2 curve and by applying another 2.2 in the frame buffer you double gamma correct it to 4.4 so it looks too bright/washed out.

That's the sole purpose of applying texture input gamma which in turn reverses the curve of the texture from 2.2 to 1 and then when you work in linear environment where everything else is 1, its correctly displayed.

For which textures need a gamma curve which do not, pretty much every texture except 32 bit float texture needs a gamma curve, you should be careful with 16 bit textures too. Exr/Hdr do not need gamma curves as they come with their own and renderer respects that.

[beenyweenies]

Thanks for the reply!

I'm familiar with these concepts in general, but sometimes I'm not sure what the use cases are on these specific options. If I'm understanding things correctly, ANY and ALL 8/16 bit images with an sRGB profile are assumed to be 2.2 gamma, and that's why there's no adjustment option when sRGB is selected. But if the image has a different curve for whatever reason, including if it's an sRGB image but with a custom curve, you would use the explicit Gamma setting?

Does this mean that using the default explicit Gamma setting of 2.2 will give the exact same result as setting it to sRGB?

[Morbid Angel]

Yes that's correct.

It really comes down to - what looks best. I often color correct textures in maya as end result. You could do it in photoshop but if its faster with less steps why not? I can tweak the gamma a bit to make the texture more contrasted for example - its not rocket science, one does not need to adhere to exactly strict numbers here....That's why I love what we do!

[beenyweenies]

one does not need to adhere to exactly strict numbers here....That's why I love what we do!

I agree! I guess a logical follow-up to this line of discussion is this - what's the thinking around using other profiles in file textures, like Adobe RGB, given their wider range?

[Morbid Angel]

I'm not sure. Wider range as in what exactly? and 8 bit is an 8 bit, you can't go higher in range then that. People tend to generally stick to common values for ease of things.

[beenyweenies]

I'm not sure. Wider range as in what exactly? and 8 bit is an 8 bit, you can't go higher in range then that. People tend to generally stick to common values for ease of things.

I'm sorry I should have been more clear. What I meant is that the Adobe RGB color profile has a wider color gamut than sRGB, i.e. can represent a wider range of color. I'm mostly wondering if Maya 2016's color management now means that it can respect profiles beyond sRGB.

[Morbid Angel]

I haven't used maya 2016 so I don't know. The more important question here would be, if it does - will vray support that?

[vlado]

I haven't used maya 2016 so I don't know. The more important question here would be, if it does - will vray support that?

Not yet.

Best regards,
Vlado