Convert pnm to raw Online: pnm2raw
You can use Tom's Editor to easily convert images from
Portable aNy Map .PNM to RAW Dump
Tom's Editor is a free, online image manipulation and converter program.
Go to Tom's Editor
PNM images are uncompressed 24 bit RGB images. Can cannot store Alpha channel. PNM images come in 2 types: binary and text. Especially popular on Linux.
This is just raw pixels saved in a file. Format used mostly by old games. RAW files do not have any header so if you don't know what is the original width and height of the image it might be hard to decode them.