Convert an ILBM file to a PPM image. More information: https://netpbm.sourceforge.net/doc/ilbmtoppm.html.
ilbmtoppm path/to/file.ilbm > path/to/file.ppm
ilbmtoppm -transparent color path/to/file.ilbm > path/to/file.ppm
ilbmtoppm -ignore chunkID path/to/file.ilbm > path/to/file.ppm
ilbmtoppm -maskfile path/to/maskfile.pbm path/to/file.ilbm > path/to/file.ppm