Free Hero Mesh class resource file
A Free Hero Mesh puzzle set consists of four files; this article is about the .xclass file, which contains pictures and sounds.
This file is a Hamster archive which contains lumps with extension .IMG and .WAV.
The .IMG lumps are pictures, using a specialized compression format. Each such lump can store multiple versions of the picture at different sizes (which must be square, but otherwise can be arbitrary), and use a fixed palette of 255 colours plus transparency.
The .WAV lumps are WAVE audio files.