Blend modes

b BLEND - linear interpolation of colours: C = A\*factor + B. This is the default blending mode.
a ADD - sum of A and B
d DARKEST - only the darkest colour succeeds: C = min(A\*factor, B).
l LIGHTEST - only the lightest colour succeeds: C = max(A\*factor, B).
f DIFFERENCE - subtract colors from underlying image.
e EXCLUSION - similar to DIFFERENCE, but less extreme.
m MULTIPLY - multiply the colors, result will always be darker.
s SCREEN - opposite multiply, uses inverse values of the colors.
r REPLACE - the pixels entirely replace the others and don't utilize alpha (transparency) values.
[not used] REMOVE - removes pixels from B with the alpha strength of A.
o OVERLAY - mix of MULTIPLY and SCREEN . Multiplies dark values, and screens light values. (2D)
z HARD_LIGHT - SCREEN when greater than 50% gray, MULTIPLY when lower. (2D)
x SOFT_LIGHT - mix of DARKEST and LIGHTEST. Works like OVERLAY, but not as harsh. (2D)
g DODGE - lightens light tones and increases contrast, ignores darks. (2D)
u BURN - darker areas are applied, increasing contrast, ignores lights. (2D)