NAMEppmmix - blend together two portable pixmaps
SYNOPSISppmmix fadefactor ppmfile1 ppmfile2
DESCRIPTIONReads two portable pixmaps as input. Mixes them together using the specified fade factor. The fade factor may be in the range from 0.0 (only ppmfile1's image data) to 1.0 (only ppmfile2's image data). Anything in between gains a smooth blend between the two images.
The two pixmaps must have the same size.
is a more general alternative. It allows you to mix images of different
size and to have the fade factor vary throughout the image (through the
use of an alpha mask).