invert_raw_image - invert 2D image along either or both axes
invert_raw_image xsize xsize [bytesperpixel]
invert_raw_image reads an image from standard input and copies it to
standard output, inverting along either or both dimensions according to
the arguments.
The parameter xsize specifies the number of pixels in the x-direction.
Use a negative number to flip the image along this axis. Ditto for
ysize. The number of bytes per pixel defaults to 1 if not specified.