

   For debugging, pixDisplay() and pixDisplayWithTitle() in writefile.c
   can be called to display an image using one of several display
   programs (xzgv, xli, xv, l_view).  If necessary to fit on the screen,
   the image is reduced in size, with 1 bpp images being converted
   to grayscale for readability.  Another common debug method is to
   accumulate intermediate images in a pixa, and then either view these
   as a mosaic (using functions in pixafunc2.c), or gather them into
   a compressed PDF or 