A computer implemented method of processing image pixel data corresponding
to an image pixel comprises determining if the image pixel is opaque or
transparent. If the image pixel is determined to be opaque, a pixel color
value from a first set of image pixel data is determined. If the image
pixel is determined to be transparent, a transparency value from a second
set of the image pixel data and a pixel color value from a third set of
the image pixel data is determined. The second and third sets of the
image pixel data are subsets of the first set of image pixel data.