Convert art to pgm

What is the difference between .art and .pgm?

Description: PFS Art Publisher Image (ART) is a raster graphics file format used for storing digital images. It was developed by Progressive Networks for use in their Progressive FreeStyle Art Publisher software. ART files are compressed using the run-length encoding (RLE) algorithm, which allows them to store large images in a relatively small file size. The ART format supports up to 24-bit color and is often used for storing digital photos and other images.; A PGM file is a grayscale image file saved in the portable gray map (PGM) format and encoded with one or two bytes (8 or 16 bits) per pixel. It contains header information and a grid of numbers that represent different shades of gray from black (0) to white (up to 65,536). PGM files are typically stored in ASCII text format, but also have a binary representation.