This program is part of Netpbm. sirtopnm reads a Solitaire Image Recorder file as input and produces a PNM image as output. The type of the output file depends on the input file - if it's an MGI TYPE 17 file, sirtopnm generates a PGM file. If it's an MGI TYPE 11 file, sirtopnm generates PPM. The program tells you which type it is writing.