.PNJ File Extension

The PNJ format is a hybrid of the .PNG and JPEG formats. Each PNJ file contains JPEG-encoded image data saved within a PNG container. This allows PNJ files to include an alpha channel, like PNG files, while still being compressed using lossy compression (reducing their file size in comparison to PNG files).

The PNG Development Group created the PNJ format for use alongside the .MNG (Multiple-Image Network Graphic) format. Each MNG file can be comprised of multiple PNJ files, used to show an animation. However, both MNG files and PNJ files are quite uncommon. Thus, most image viewers and editors cannot open PNJ files.

NOTE: During development of the MNG format, the PNG Development Group renamed the PNJ format to the JPEG Network Graphic (.JNG) format.

You may be able to open a PNJ file with XnViewMP. While XnViewMP does not officially support the PNJ format, it can open many types of image files, including .JNG files (to which PNJ files are related).

At this time, there is no known program that officially supports the PNJ format.