ppmmix
Blend together two PPM images.
TLDR
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]
Blend the specified PPM images using fadefactor to control the weight of each image