Convert j2k to jpg Online: j2k2jpg

You can use Tom's Editor to easily convert images from
JPEG-2000 Code Stream Syntax .J2K to Joint Photographic Experts Group JFIF .JPG.
Tom's Editor is a free, online image manipulation and converter program.

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J2K

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

JPG

Joint Photographic Experts Group JFIF is an image format with extension JPG.