Patent ID: 7200277
Filing Date: 2007-04-03
Classification: H04N

Abstract:
1. A method for transcoding a JPEG2000 compressed image comprised of a collection of sub-bands encoded in one or more coding passes into a compressed bit-stream of quantized sub-band coefficients partitioned into codeblocks of each sub-band and aggregated into layers, said method comprising the steps of: (a) parsing a JPEG2000 compressed image to extract header information and packets; (b) calculating the number of bytes associated with each layer at a user-specified desired resolution to produce a layer byte-count table; (c) estimating the number of layers of the JPEG2000 compressed image that should be decoded up to the user-specified desired resolution for transcoding to a user specified desired bit-rate; (d) extracting packets belonging to resolutions up to the user-specified desired resolutions from the layers to be decoded as determined in step (c), and extracting compressed data corresponding to each codeblock that contributed to the packets; (e) concatenating the compressed data corresponding to each codeblock, extracted in step (d), to produce a compressed codeblock bit-stream for each codeblock; (f) arithmetically decoding the compressed codeblock bit-stream corresponding to each codeblock to produce a quantizer index for each subband coefficient and a coding pass length table, which contains an estimate of the length of the compressed data corresponding to each decoded coding pass; (g) producing an operational rate-distortion table for each codeblock from the quantizer indices and the coding pass length table produced in step (f); (h) producing coding pass inclusion information, which represents the coding passes that should be included in the transcoded bit-stream, using the operational rate-distortion table produced in step (g), the desired bit-rate and a plurality of user-specified visual weights; and (i) producing a transcoded JPEG2000 bit-stream from the compressed codeblock bit-streams produced in step (e), the header information extracted in step (a) and the coding pass inclusion information produced in step (h).