Patent ID: 7177479

Claim:
A method of compressing a stream of pixel data relative a two-dimensional object, pixels of which are scanned by rows from a source device to a receiver device, the method comprising: calculating a context value representative of a level of differences among pixels that are included with a pixel currently being processed within a context window having predefined dimensions, the pixel currently being processed includes a last processed pixel and a triplet of neighboring pixels belonging to a row preceding the row being scanned and to which the current pixel belongs; defining an extended context window to include a pair of pixels following a last encoded pixel on the row being scanned and the respective triplets of neighboring pixels belonging to the preceding row; defining a first distinct context array of pixels of the extended context window for the pixel of the pair immediately following the last encoded pixel, and a second context array of pixels of the extended context window for the other pixel of the pair; calculating a set of local gradients relative to each pixel of the pair based upon acquired values thereof; calculating from the calculated local gradients an extended context value relative to each pixel of the pair; and comparing the extended context value relative to a first pixel immediately following the last encoded pixel with an extended threshold, the comparing comprising if the extended context value is less than the extended threshold, then encoding the first and second pixels of the pair, and if the extended context value relative to the first pixel of the pair exceeds the extended threshold, then carrying out simultaneously a parallel processing and encoding of both pixels according to an encoding routine reading data from distinct context tables of stored statistics of previous predictor errors relative to the pixels of the extended context window for the respective pixels of the pair.