Convert hgr to pnm Online: hgr2pnm
You can use Tom's Editor to easily convert images from
High Resolution .HGR to Portable aNy Map .PNM.
Tom's Editor is a free, online image manipulation and converter program.
Go to Tom's Editor
High Resolution is an image format with extension HGR.
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.