Understanding Linear Workflow in Vray for Sketchup

brooklynia373

Hi all,

I've seen the conversation about linear workflow started a couple times on here. I've spent the last couple days trying to understand this with little headway. Am I right that Vray is already set up for this workflow but that some extra settings are needed? Any help or corrections to my understanding would be greatly appreciated. It's likely I'm over-thinking all this.

Here's what I think I know:

1-gamma correction is needed to make sure images are bright enough and color correct when displayed on a monitor.
2-most images used for diffuse textures that are pulled from internet already have gamma correction applied.
3-the goal with linear workflow is to A: remove this gamma correction from all textures prior to rendering and B: to apply gamma correction only once, globally, at either the render stage (inside Vray) or post-production stage (inside PS.) (NOTE: bump, specular, and displacement maps do not need to be adjusted for linear workflow. They only need to be set to RGB "color space" to preform correctly.)

Is this right?

How do I de-gamma my diffuse bitmaps? Do I set the "gamma correction" value to .454 inside each material's texture editor? Or do I do this in the COLOR MAPPING roll-out by setting the "Input gamma" to .454? Or do I check "Correct LDR textures" and "Correct RGB colors?" None of these? All of these? IDK

What about on the output side of things? It would be great if someone had a pic of their COLOR MAPPING settings for this.

Also, do any of these setting change if I'm outputting separate channels to composite later in PS? I've read saving as a tga. file is best because it's 32 but, unlike exr, you get the full range of adjustment layers in PS.

Thanks for the help.

VRAY 2.0 and SU 2016 Pro

filibis

Here is a nice and brief official tutorial from Vray: Introduction to Compositing. (Part 1 answers your most questions)

Also this tutorial explains the linear workflow in general really good. (It's for 3ds Max but it's good to understand the concept, also it applies to other softwares as well)

I also suggest reading 'color mapping' part of this article for Vray 3. It gives you some good hints related to previous version linear workflows as well as how they implement in the new version.

brooklynia373

thanks filibis. maybe this topic is outdated from lack of response.

I'd been following the compositing tutorial and the article on Vray 3 was helpful. looks like a lot of the guess work is removed for the latest version.

I'm still wondering how to handle pre-gamma-corrected textures from the internet...

But I did learn that I was misinformed and .tga's are not 32 bit. Exr's are best.

filibis

@brooklynia373 said:

I'm still wondering how to handle pre-gamma-corrected textures from the internet...

I think all 8bit images (.jpg) are already 'gamma corrected' which means 2.2 gamma is already applied. I believe that's the reason why we define 'Input gamma' 2.2, so that Vray understands it (and it's by default in Vray 3).
And if you have a 16bit or 32bit image (.tif or .exr), i think Sketchup Vray understands it automatically, so either way there's no need to worry.

This pdf document explains it very well.

Upgrade to Vray 3.4 and lean back (Not to mention it's significantly faster and has more features...)