This is a format that is used for RAW images on Nikon cameras. It contains metadata about the lenses that were used to take the photo, capture settings, and other conditions. It provides a record of the data array obtained by the camera sensors through the lens. It allows you to edit the sharpness, colors, and tones with no loss to the content or quality of the image, which is something that cannot be done with compressed images. It supports 12- and 14-bit images.
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.