This is an encoder for JBIG2.
JBIG2 encodes bi-level (1 bpp) images using a number of clever tricks to get better compression than G4. This encoder can:
Generate JBIG2 files, or fragments for embedding in PDFs
Generic region encoding
Perform symbol extraction, classification and text region coding
Perform refinement coding and,
Compress multipage documents
It uses the (Apache-ish licensed) Leptonica library: http://leptonica.com/