This demonstrates the use of PNG_USER_CONFIG and pngusr.h

The makefile builds a minimal write-only decoder with embedded libpng

and zlib.

Specify the location of the zlib source (1.2.1 or later) as ZLIBSRC

on the make command line.

If you prefer to use the shared libraries, go to contrib/pngminus

and build the pnm2png application there.