Abstract: A post-processing method and apparatus are described whereby a second image is formed by horizontally shifting pixel primitives of a first image by an amount determined by their respective depths to give a parallax shift. To avoid gaps appearing in the shifted image, two z-buffers are maintained during rendering of the first image with the second being loaded by discarded values of the first such as to provide a record of the first occluded primitive for each pixel. The horizontal shift is applied to the contents of both z-buffers and the results written to a third z-buffer such that gaps due to the varied shift applied to the first image values (the unshifted contents of the first buffer are filled by previously occluded values from the second buffer. The two images may then be output to a suitable stereoscopic display such as a Virtual Reality headset.