You would just add it to your master material as a bool, so that it can be enabled as needed on any instances with the click of a button. The issue with tinting the scene blue as a post process is that areas that are in direct light don’t need to be adjusted, so you cannot linearly apply color correction to the screen.
I have also figured that it is best to cut the R&G instead of boost the B. This is because albedo is clamped from 0-1. In the unlikely event that you have a very high albedo value, boosting will get clamped and not correct the scene. So for example you might multiply the RT pass by ( 0.946, 0.946, 1) instead of ( 1, 1, 1.054). I tried more scenes and lighting configurations and found that the 4-6% range generally offered the most aesthetically pleasing results.
Both R&G and B will suffer from lost precision at certain values in the GI texture. So my theory is the important figure is the difference between how imprecise they are.
I believe the range, more specifically 5.4% or (0.946 RG) is the ideal ratio for white balance after doing lots of math and testing.
Based on the images below. I’ve tested the RGB values in multiple lighting setups and this offers the consistently truest white based on my experiments. Using these values, here are the histograms side by side.
EDIT: swapped comparison out for a brighter image to better show differences.
OG Lumen Left, Shifted Lumen Middle, PT Right:
Note that the color shifted lumen does a good job of shifting the color peaks to by synchronized. It’s not perfect, but this is in an extreme case with an albedo of 0.9. I did not increase the indirect light intensity of this example.
OG Lumen:
Shifted Lumen:
PT:
Shifted Lumen with increased indirect light:
Edit: For science, here’s the histogram of shifted + boosted Lumen (left) vs Pathtracer (right). I didn’t fine tune the indirect light boost, just got it roughly by eye. Once again, still more color inaccuracy than the PT, but the peaks and troughs are all in the right place and the RGBs mostly overlap.
In this specific scene I had to double the indirect light intensity of Lumen to roughly match the Pathtracer. I don’t think that is representative of a typical case - we’re just in an almost pure white box and the PT does a better job of bouncing all that light around.
Sliding Comparisons:
Shifted vs PT
Shifted vs OG
Pathtracer vs OG
Shifted + Boosted vs Pathtracer: