Convert grf to pnm Online: grf2pnm
You can use Tom's Editor to easily convert images from
GRF, MAX, P41, PIX .GRF to Portable aNy Map .PNM.
Tom's Editor is a free, online image manipulation and converter program.
Go to Tom's Editor
GRF
GRF, MAX, P41, PIX is an image format with extension GRF.
PNM
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.