Patent FR-2835366-A1 (FR)
Title: Method and device for the forming of a reduced compressed digital signal
Inventor: LE LEANNEC FABRICE
IPC: H04N7/26
Filed: 2002-01-29
Abstract: The reduced compressed digital signal is formed on the basis of an initial digital signal compressed to several hierarchical levels which are obtained by compressing a digital signal comprising data representative of physical quantities. The initial signal so compressed comprises at least one header which contains the information representative of the signal configuration and the data structure, and the signal configuration is defined by an initial set of parameters characterising the set of hierarchical levels of the signal. The method comprises the following steps: forming at least one header of the reduced compressed signal which contains the information representative of a reduced configuration of the initial signal and the data structure in the compressed signal, where the reduced configuration is defined by a final set of parameters characterising at least one of the hierarchical levels of the compressed initial signal; extracting (E4) the compressed data corresponding to the final set of parameters on the basis of the compressed initial signal; and inserting by concatenation (E5) the data into the reduced compressed signal in forming.  The method comprises the steps of extracting and inserting (E7) of at least one header of the compressed initial signal into the reduced compressed signal in forming, and modifying at least one inserted header as a function of the inserted compressed data. At least one inserted header contains several fields, and the fields are determined by a test preliminary to the modification step. The method comprises the steps for obtaining the information representative of the reduced configuration of the initial signal and the data structure corresponding to the reduced configuration, and for inserting the information into the reduced compressed signal in forming in order to form at least one header of the signal. When the digital signal is an image signal, the final set of parameters contains at least one parameter from among the resolution level, the quality level, and the signal component. The method comprises the step for simplifying (E13) the structure of the reduced compressed signal. The compressed data of the reduced compressed image signal are organized in data packets (P), which are in turn organized in blocks of ordered data. Each packet comprises a packet header and a packet body containing the blocks of data, and corresponds to a reduction level, a quality level, and a signal component. When the initial signal is decomposed into frequency sub-bands, a packet corresponds to a set of data blocks of the decomposed signal. The simplification of the signal structure for each level of resolution of the reduced comprssed signal comprises the steps for merging the headers of different packets into one header of data packet, and merging bodies of different packets into one packet body, which includes a reordering of data blocks. The reordering of the packet body for a given level of resolution is according to the spatial distance of the blocks conforming to the syntax of the signal description. The contributions of the same data block to different quality levels are concatenated in the increasing order of levels for a given resolution level. A device for forming the reduced compressed digital signal is claimed and implements the method. Independent claims are also included for an apparatus for data processing which comprises the device, means for storing the information readable by a computer comprising the instructions of a computer program code for executing the steps of the method, removable means for storing the information and a computer program which can be loaded into a programmable apparatus.