The format is designed for Kodak cameras to store uncompressed RAW images in their original form without auto color and white balance correction. The file has a TIFF-structure that allows you to edit the color temperature and exposure of the finished image without losing information and quality, which is something that cannot be done with JPEG format images.
PPM is a simple format for storing images portable pixmap: color (PPM), grayscale (PGM) and black and white (PBM). These formats can provide an intermediate representation of the data when converting raster image files listed three types between different platforms. PPM format was developed by Jeff Poskanzerom.