The previous math forms are the only truly accurate description of each blending operation, but short descriptions are below where Source is the output from the next track and Destination is the output from the lower track stacking. Blending starts with new Source and combines it with the previous render stack output, which is referred to as Destination. The new output becomes the next Destination and the next up stack level becomes the new Source. Source is above; Destination is below.
Note: the Graphic Art group operates principally on color, and the others operate principally on alpha.