Patent ID: 7187802

Claim:
A method of progressive joint photographic experts group (JPEG) decoding, being used for decoding a JPEG bit stream as image data indicative of an image in an apparatus for JPEG decoding, the apparatus including a memory, the method comprising the steps of: receiving data indicative of a scan in the JPEG bit stream; dividing the data indicative of the scan into a plurality of regions; selecting one of the regions as a decoding region; decoding the data indicative of the scan into a plurality of decoded coefficients for each of the plurality of regions; producing a corresponding nonzero history of each of decoded coefficients of remaining regions according to data corresponding to the remaining regions, wherein the remaining regions are the regions of the scan except the decoding region; and storing the decoded coefficients of the decoding region in the memory; storing the corresponding nonzero history of each of the decoded coefficients of each of the remaining regions in the memory, wherein the nonzero history indicates whether one associated decoded coefficient is zero and the size of the nonzero history is smaller than the size of one associated decoded coefficient; and outputting the decoded coefficients of the decoding region, which are indicative of a portion of the image data; wherein the corresponding nonzero history of each of the decoded coefficients of each of the remaining regions, other than all of the decoded coefficients of each of the remaining regions, are stored for Huffman variable length decoding in decoding the JPEG bit stream so as to reduce the resource of the memory required for decoding the JPEG bit stream as the image data.