An image rendered by a non-alpha-channel-aware application is employed in an
alpha-channel-aware
environment. The pixel data file to be written to by the non-alpha-channel-aware
application is initialized by setting the alpha value for each pixel to 1. The
alpha-channel-aware application then writes to the initialized pixel data file,
changing some or all pixel data. The alpha value for each pixel is then decremented
by 1 (modulo 256) making the changed pixels opaque and the unchanged pixels transparent.