 output is to go to stderr, compile with -DNO_CONSOLE_IO.

   Runtime redirection of stderr output is also possible, using a
   callback mechanism.  The callback function is registered using
   leptSetStderrHandler().   See utils1.c for details.

7. In-memory raster format (Pix)

   Unlike many other open source packages, Leptonica uses packed
   data for images with all bit/pixel (bpp) depths, allowing us
   to process pixels in parallel.  For example, rasterops works
   on all depths with 32-bit parallel 