I was wondering if anyone could break down the differences between these (overlay layer mode, color layer mode and maybe even multiply layer mode) in a good way in relation to digital painting - i.e. painting a monochromatic underlay and putting color on afterwards...
Darken/Lighten : Any pixel with a brightness lighter/darker than the pixel on this layer will get replaced by this pixel completly.
Multiply/screen : Multiply multiply's the darkness of the layers pixel with those below
so over white they are unchanged, over darker values they are darkened. Screen does exactly the reverse. You have to just play with them a bit... its kinda hard without getting into the maths I guess. Screens great for replacing black and white with colours like screen-printing (might be where the name comes from) and multiply is great for putting linework over an image without any white.
A pixel on a COLOUR layer replaces the hue and saturation of the underlying layer with its own the hue and saturation without effecting its brightness.
A LUMINOSITY Layer replaces the brightness of the underlying layer without effecting hue or saturation. A luminosity&colour layer combined has the effect of just a normal layer which replaces the HSV value completly.
OVERLAY is a combination between multiply and colour dodge or something similar... if the pixel is 50% grey it does nothing... if its darker it multiply's if its lighter it lightens, but in a way similar to 'curves' ie it never touches black and the darker the underlying pixel is, the less it is effected.