The new colour management in Mari 3 can be a little bit tricky to grasp at a first glance. Lets examine it from a artist perspective.
First off we have to know some basic principles when it comes to rendering the textures we paint. A render engine always assume that all values are linear. Most of our source images we find on texture resources or we acquire ourselves probably has a gamma curve baked into the image.
What is gamma?
Really simplified its an adjustment curve, neither our eyes or our monitors have a linear response. A dslr camera sensor captures the light linearly in its raw state and if you would take the data and view it on a regular monitor the image would look dark contrasty and saturated. To compensate the iamge we output from the camera gets a gamma curve applied to it so it displays as we expect it to look like when we captured the image.
We have a few options how to paint. We can go all linear or still paint with gamma encoded values and choose what we want the end result to be output to. In mari 3 we had open colour introduced and internaly mari linearise the colourdata to its working colorspace. This is similar to how Nuke handles the colourdata.