I heard someone used luminosity masks to do the painting. I tried to do the same with a file I created for RGB format rather than LAB format. Only the LLL and L were used. Ignoring the time it takes for me to create instanced layers for automated editing, this took me only about 2 minutes to do. If more efforts than 2 minutes were applied, then this would be much better. This was a test of how effective luminosity mask can be.