Method and apparatus for storing a two-dimensional image representing a

Abstract

A method of generating a two-dimensional image representing a three-dimensional scene is describerd. The method comprises: (a) storing a set of foreground pixel data and at least one set of background pixel data, each such set defining a color and a depth for each pixel of the image; (b) selectively modifying the stored foreground and background data in response to a series of input pixel data defining color and depth for a series of pixels of the image; and (c) forming output pixel data by combining the stored foreground and background color for each pixel in proportions defined by a mixing value associated with that pixel. In one embodiment, step (b) comprises selectively modifying the stored data depending on the input depths so that: (i) if the input depth is greater than the stored foreground and background depths, the stored foreground and background pixel data are left unchanged, (ii) if the input depth lies between the stored foreground depth and the stored background depth, the input pixel data is stored in place of the background data for that pixel, and (iii) if the input depth is less than both the stored foreground and background depths, the stored current foreground data for that pixel are stored in place of the stored background data and the input data are stored in place of the current foreground data. An arrangement is described for performing the method. The arrangement may form part of an electronic graphics system.