confused with gamma correction

[hotchicken]

I've seen a video tutor by gnomon about antialiasing, in which the guy turned on a setting in gamma called "adaption only", to cheat vray, so that it calculates noise in a gamma corrected way but exports the picture intact(if i understand it right..)

is checking the "adaption only" the same as unchecking "correct RGB" in vfr?
and what is a correct linear workflow, which everyone talks about? sorry i've read a lot of the posts here but got more confused afterwards...

thanks a lot

[dalomar_cg]

Re: confused with gamma correction

You've opened up a pandoras box...prepare for a complete barage of information...

The main reason why the "adaptation only" option was added to vfMax was for compositors. Basically they calculated their image in gamma corrected space, but during compositing, they needed to the image in Linear color space for an accurate composite. The solution was to calculate without the output gamma correction (inputs would still be corrected), so that the compositing could be done in linear space and the gamma correction could be applied later.

In comes the issue. Because the ungamma corrected output would be essentially darker then the gamma corrected version, the sampling of the image would not be accurate for the final version (check out adaptive sampling if you want to know the specifics of why v-ray does that). So you either deal with it, or change you're settings to more than what you needed so that the final result was clean. All of this is because the gamma correction was applied later on.

So the "adaption only" setting, means that v-ray "knows" that the image will be gamma corrected, and therefore calculates it as such, but doesn't actually apply the gamma correction to the final output. Later on, when the gamma correction is applied, then the final result will be correct and accurate, without oversampling anything.

On our side of things, we handle the gamma correction a little bit differently then Max does. We have an input and output gamma value, then the input correction options; correct LDR textures, correct RGB values. This will allow you to more easily set gamma correction, is enabled by default, and is a correct method for linear workflow. The "adaption only" setting is currently not in the released version, and there isn't a setting that would be the equivalent to that setting for the reasons I described above. If you did need to have your image saved in linear space but inputs still corrected, you could set the output gamma to 1, yet leave the input at 2.2 and Correct LDR/RGB enabled. This will leave you with the same dilemma as before...deal with the slightly grainier result or increase the sampling.

I hope that makes sense

[hotchicken]

Re: confused with gamma correction

thanks a lot
it's definitely helping me out