TGA is a raster graphic format. It was originally created by Truevision Inc. for graphics cards has its own production in 1984, but later became popular on a variety of platforms, especially in the field of video editing, animation. Format supports color depths 1-32 bits per pixel. There is support for alpha channels, compression RLE.
PGM is a storage format for grayscale images. Files in this format can be opened using software: ACDSee Photo Manager 14, ACD Systems Canvas 15, Corel PaintShop Pro X4. This type of file can be edited with a text editor. PGM files can be in two versions: P2 / P5. P2 are readable, P5 - to binary formats.