The default viewer for any image in Xubuntu is Ristretto Image Viewer.
Using Xubuntu 16.04 LTS, it was possible to read
image.ascii.pgm with Ristretto. With 18.04 the program opens but no images are displayed.
- Is there a way of reading
image.ascii.pgmfiles with the Ristretto Image Viewer in Xubuntu 18.04 LTS?
- If not, do you suggest to use another viewer instead? If so, how to use another viewer as default?
Temporary workaround: I can read the images using Inkscape, but, as you can imagine, it is not a light-weight viewer program; it is a heavy vector-graphics image editor (like shooting a fly with a cannon).
ASCII PGM (Portable Gray Map) format for 2D grayscale graphics information. More info here.