Convert j2k to pnm Online: j2k2pnm

You can use Tom's Editor to easily convert images from
JPEG-2000 Code Stream Syntax .J2K to Portable aNy Map .PNM.
Tom's Editor is a free, online image manipulation and converter program.

Go to Tom's Editor

J2K

JPEG-2000 Code Stream Syntax is an image format with extension J2K.

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.