This is a color model display format that uses the three primary colors (blue, red and green) to create an image. Each color can have up to 255 gradations, allowing for color depths of up to 48 bits. RGB supports the display of 16,777,216 colors.
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.