Transparency group computation on a graphics processing unit

A new transparency group may be rendered and blended with other, previously rendered, transparency groups, by using the Porter-Duff algebra available on the GPU even though the transparency groups include pre-multiplied color and alpha information. Additionally, the number of copies of the back buffer (the image information for the previously rendered transparency groups) required to properly render, blend and combine the new transparency group into the image information of previously rendered transparency groups may be minimized.