Patent ID: 7194033

Claim:
A method of forming a sequence of images for transmission over a communication network, said method comprising the steps of: forming representations of plural graphical object-based images; rendering the images in a sequence using a computer graphics application, the rendering comprising: determining a set of changes required to transform a previous image in the sequence into a current image in the sequence, and indicating the changes in a format known to an encoder a priori; encoding the sequence using said encoder such that the encoder utilizes at least one of the changes to optimize encoding of the current image; and storing an encoded representation of at least the current image for use in an encoding of a subsequent image in the sequence, wherein said encoded representation comprises a plurality of separately encoded discrete portions, and wherein the set of changes comprises a change to a compositing tree by which the object-based graphical image is described, the change indicating a portion of a rendered current image having changed, said encoding comprising determining the discrete portions that require update as a result of the change, encoding rendered pixel values output from the computer graphics application corresponding to the changes as replacement ones of the portions, and combining the replacement portions with remaining portions of the preceding encoded image to form a current encoded image.