1. A method of producing a computer display image that includes depth of field information, the method comprising: producing a sharp image of a scene; producing a blur image of the scene; and producing an alpha channel RGBA image comprising a composited blend of the sharp and blur images and z-buffer image data such that the produced alpha channel RGBA image provides an image having depth of field information when the alpha channel RGBA is received by a graphics processor and rendered for display on a computer display device.