le packing the resultant pixels in a format that
    is optimized for the application.  This alternate format might be very
    different than the 8-bit per sample ABGR format the library writes by
    default.  For example, if the application is going to display the image
    on an 8-bit colormap display the put routine might take the data and
    convert it on-the-fly to the best colormap indices for display.
  </p>
  <p>
    The last item permits an application to extend the library
    without modifying