This format is used for storing bitmap images with improved levels of color and brightness performance. It combines exposures to record darker tones in the shadows or detail in the lighter areas of a given photo. HDR is able to combine multiple images with different levels of light distribution. It is used to create rich 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.