reflection amounts in a gamma 2.2 workspace

#1

Hello everyone!

I use Max 10 and Vray 1.5 and have recently moved over to a linear workflow and gamma 2.2. and saving the images as 32 bit floating point openEXR. I have seen tutorials where to create a white surface for example you would not use a color of 255 because that would be unrealistic and possibly give you strange artifacts. “White” in gamma 2.2 is more like 170±. The question now is how does this affect the colors you choose for reflection or refraction amounts? I am getting some weird hot white pixels that flicker and move around in areas of heavy reflection like chrome and other metals and I am thinking that its because the reflection amounts are no longer based in realty and possibly are trying to display something above 255. Does anyone have any thoughts or rules of thumb on this topic?

Thanks for any help.

#2

Could you pl post and example? Because i get the impression you are mixing some stuff here.

Flickering white pixels shouldnt be caused by linear workflow. Make me rather think you arent using enough sampling.

#3

Thanks for the reply but I figured it out. I know what you mean by the sampling not being high enough but that has a certain ‘look’ and this was not it. It was basically the combination of reflection values being too high, the Vray sun being visible, and using an unclamped file format ( 32 bit openEXR ) that seemed to produce the hot pixels.

Thanks!

#4

Clamping the output and activating subpixel mapping in the Color Mapping section does away with nasty white splotches. Just make sure you aren’t clipping any colors you want to keep.

#5

Thanks for the feedback. I might try that as well…

#6

but when doing this keep in mind that you lose the dynamic range when clipping and using subpixel mapping does not give physical correct results.

What i like to do when i have ‘harsch highlights’ is render at twice the resolution and scale the image down. Just be sure to do it as a last step (after all postwork is done)

#7

I know but I was happy that someone was trying to help! The original question still remains however. When working in a LWF with gamma 2.2 the equivalent of 50% gray is really more like 55 as opposed to 128 in color but what about reflection values? If you wanted to have 50% refelction would that value be 128 gray or 55 gray?

#8

any map that affect the color of the map should be gamme corrected.

any masked type of maps (that includes the reflection map in vray as it acts like a mask for the reflections) should not be gamma corrected.
Bump maps also dont need to be gamma corrected.

This is because the gamma of 2.2 (or anything else you set it at) wil be applied to the color output of the render.

#9

I believe 128 will not be 50% reflective, it will be more. That is the way it always seemed to behave for me. I’m curious if this is true, because I’m relatively new to LWF as well. But, in the end I tend to just do what looks right and exact reflective values don’t usually matter in my work.

#10

Here’s my guideline for when to use or not use gamma correction:

Is the texture affecting the output color of the object in any way? Doesn’t matter if it’s via diffuse, reflection, refraction, SSS, etc. If the texture imparts any type of color info to the render, it gets gamma corrected.

A gold metal shader is the perfect example here.

Basically I’ll only leave roughness, transparency and bump un-gamma corrected.

Edit: and 0-1 single channel maps such as reflection amount, diffuse amount etc.

If you’re doing grayscale-only reflection/refraction maps… well, I personally gamma correct them too. But I’m not a slave to the numbers… generally stuff will go directly into an HSV remap after a gamma correct (talking Maya here) for a liberal amount of easy tweakability.

But, I’m also one of those guys who won’t touch the magic “linear workflow” button and prefers to see gamma nodes in all my shading networks so I know what’s going on at every point. Your mileage may vary.

–T

#11

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