Decoder for selectively decoding predetermined data units from a coded bit stream

摘要

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.

主权项

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.