ppmmix

Blend together two PPM images. More information: https://netpbm.sourceforge.net/doc/ppmmix.html.

Blend the specified PPM images using fadefactor to control the weight of each image:

ppmmix {{fadefactor}} {{path/to/input_file1.ppm path/to/input_file2.ppm ...}} > {{path/to/output_file.ppm}}