Patent ID: 6985161

Claim:
A method of generating a pixel image, the image being formed by rendering and compositing a plurality of graphical objects according to an expression tree representing a compositing expression for the image, the expression tree comprising a plurality of nodes each representing one of the objects or an operation for combining objects or results of other operations, each of the objects comprising a predetermined outline and one or more attributes associated therewith, said method comprising the steps of: for at least one object node, forming one or more mutually exclusive regions, each of the mutually exclusive regions being defined by a region outline substantially following at least part of the predetermined outline of the object, each of the region outlines being formed from horizontal and vertical segments of a virtual grid encompassing a space in which the predetermined outlines are defined, the virtual grid comprising a plurality of cells, each cell comprising a plurality of pixels both horizontally and vertically there within, wherein each of the mutually exclusive regions has one or more attributes associated therewith depending on the attributes associated with the object; for at least one operation node, forming a plurality of further mutually exclusive regions, each of the further mutually exclusive regions being formed from the horizontal and vertical segments corresponding to the mutually exclusive regions of one or more object nodes associated with the operation node, each of the further mutually exclusive regions having one or more further attributes associated therewith, wherein the value of at least one of the further attributes is dependent on the values of the attributes associated with a plurality of the mutually exclusive regions of the one or more object nodes, and wherein one or more of the attributes associated with the plurality of mutually exclusive regions is unused in determining the value of the at least one further attribute, thereby optimizing the determination of the at least one further attribute; and for at least one of the further mutually exclusive regions, determining pixel data from the further attributes associated with the at least one further mutually exclusive region in order to generate the image.