Decoder for selectively decoding predetermined data units from a coded bit stream
View Patent ↗A decoder ( 100 ) is disclosed, which selectively reconstructs at least one predetermined data unit out of a coded bit stream (c). The decoder ( 100 ) includes a parsing unit ( 120 ) to search and parse unambiguous information (up) characterizing the at least one predetermined data unit uniquely. Next, the parsing unit ( 120 ) provides this parsed information (up) either directly to a decoding unit ( 130 ) or to a look-up table ( 140 ) such that the decoding unit ( 130 ) could reconstruct the predetermined data unit directly out of the coded bit stream (c) based on the parsed information (up) without decoding and reconstructing the coded bit stream (c) completely. Optionally, a specification unit ( 110 ) provides an start position (us) of the coded bit stream (c) to the parsing unit ( 120 ) used for starting the search. Therewith, data traffic, computation time and memory resources could be saved for decoding and displaying e.g. compressed JPEG pictures.
1. An apparatus for decoding a region of interest (ROI) out of a coded bit stream representing a JPEG compressed image, without completely decoding the coded bit stream and without a need to insert pointers into the coded bit stream, comprising:
a multiplexer, having first and second inputs and an output
a specification unit to receive a start position of the JPEG compressed image in the coded bit stream and a user specified displacement of the ROI to produce a new start position therefrom;
a first anchor point determination unit to receive the JPEG compressed image and the new start position, the JPEG compressed image divided into a plurality of minimum coding units (MCUs) defining lines, to determine bit positions of the first bit of lines at least partly including the ROI;
a first DC-block-coefficient unit to receive the compressed image and the new start position and to determine DC-block-coefficients of the first block included in the first MCU of each line at least partly comprising the ROI simultaneously with the determination of the bit positions by the first anchor point determination unit;
a look up table for receiving the output of the first DC-block-coefficient unit and the bit positions of the first bit of each line at least partly including the ROI and for storing the DC-block-coefficient;
a second anchor point determination unit to retrieve the first bit positions of the first bit of each line at least partly including the ROI stored in the look-up-table and to provide bit positions of MCUs in the ROI of the lines at least partly including the ROI to the first input of the multiplexer;
a second DC-block-coefficient unit to receive the DC-block-coefficients of the ROI stored in the look-up-table and to provide DC-block-coefficients of blocks belonging to the MCUs in the ROI of the lines at least partly including the ROI to the second input to the multiplexer; and
a decoder for reconstructing all DCT-coefficients necessary to reconstruct each block of the MCUs used in the ROI based on the output of the multiplexer.
2. The apparatus of claim 1 , wherein the JPEG-compressed picture is divided into minimum coded units (MCUs), wherein the MCUs each comprise 8×8 pixel blocks, and wherein the ROI includes a plurality of said MCUs.
3. The apparatus of claim 2 , wherein the decoder comprises:
a predictor component determination unit adapted to calculate a predicted DC-coefficient based on preceding DC-coefficients;
a predictor unit adapted to reconstruct the DC-coefficients of each MCU at least partly comprising the ROI based on the predicted DC-coefficient provided by the predictor component determination unit or on a DC-coefficient provided by the parsing unit and on a differential value for the DC-coefficient reconstructed from the coded bit stream; and
an AC-block-coefficient-determination unit adapted to determine orthogonal transformation coefficients of each MCU at least partly comprising the ROI out of the coded bit stream.
4. A method of decoding a predetermined data unit out of a coded bit stream, the coded bit stream representing a JPEG compressed image, without completely decoding the coded bit stream and without a need to insert pointers into the coded bit stream, comprising:
producing a new start position in the coded bit stream from a received start position of the JPEG compressed image in the coded bit stream and a user specified displacement of a region of interest (ROI);
receiving in a first DC-block-coefficient unit, the JPEG compressed image and the new start position, the JPEG compressed image divided into a plurality of minimum coding units (MCUs) defining lines and determining the bit positions of the first bit of lines at least partly including the ROI;
determining DC-block-coefficients of the first block included in the first MCU of each line at least partly comprising the ROI simultaneously with the determination of the bit positions of the first bit of lines at least partly including the ROI and storing said coefficients and bit positions of the first bit of lines at least partly including the ROI in a look-up-table;
retrieving the first bit positions of the first bit of each line at least partly including the ROI stored in the look-up-table and providing bit positions of MCUs in the ROI of the lines at least partly including the ROI to a first input of a multiplexer;
receiving in a second DC-block-coefficient unit, the DC-block-coefficients of the ROI stored in the look-up-table and providing DC-block-coefficients of blocks belonging to the MCUs in the ROI of the lines at least partly including the ROI to a second input to the multiplexer;
reconstructing all DCT-coefficients necessary to reconstruct each block of the MCUs used in the ROI based on an output of the multiplexer.