Provides control over the maximum number of colours in the output image palette, making the API more closely match that of pngsave. Lowering the bitdepth to 7 (from the default value of 8), which halves the maximum number of colours from 255 to 127, typically reduces encoding time by ~20%.
libvips test suite
This is in two parts: a few simple bash scripts in this directory are run on "make check", and a fancier Python test suite that's run by Travis on each commit.