Image analysis – Image compression or coding
Reexamination Certificate
1997-07-14
2001-04-24
Boudreau, Leo (Department: 2621)
Image analysis
Image compression or coding
C382S233000, C345S205000, C348S384100, C358S426010, C708S203000
Reexamination Certificate
active
06222942
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to data compression.
The present invention is more particularly applicable to compressing messages that are intended to be displayed on the screen of equipment such as a telecommunications terminal, in particular a portable telephone, the messages being made up of words themselves made up of characters, the characters themselves being encoded so as to be stored in data-processing means internal to the equipment using a binary code such as the ASCII code, for example. In such an application, message compression makes it possible essentially to reduce the size of memory required for storing the messages, and thus to reduce the size of the circuits internal to such equipment.
BACKGROUND OF THE INVENTION
Various methods of compressing data are known, and they are described, for example, in the book entitled “Compression de données—Méthodes, algorithmes, programmes détaillés” [“Data compression—methods, algorithms, detailed programs”] by Pascal Plume, published by Editions Eyrolles.
Among those methods, reference may be made to the “Huffman” method which acts on characters and which consists in encoding characters that occur relatively frequently over a binary length that is relatively short (compared with conventional binary encoding such as ASCII encoding, for example), and in encoding characters that occur less frequently over a binary length that is longer, the resulting encoding table being conveyed to the apparatus serving to perform the inverse, decompression operation.
Such a method is not suited to compressing messages, in particular in terms of compression ratio, since said words or said messages usually include repetitive sequences of characters.
To avoid that drawback, it is possible to use a method such as the “Lempel-Ziv-Welch” method which enables such repetitive sequences of characters to be compressed by replacing them with their ranks in an encoding table referred to as a “dictionary” and created dynamically as the text to be compressed is read, and recreated in similar manner on decompression. Such a method, also referred to as “on-line textual substitution” offers a better compression ratio than the above-mentioned method. Unfortunately, its main drawback is that it requires a decompression time that is relatively long.
A particular need therefore exists for a method of compressing messages, in particular a relatively large number of messages that are relatively short and that use a relatively limited vocabulary, such as, for example, messages intended to be displayed on the screen of equipment such as a telecommunications terminal, in particular a portable telephone. This need requires in particular a method that offers a decompression time that is sufficiently short while remaining sufficiently economical in terms of compression ratio.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention thus provides a method of compressing messages, in particular messages intended to be displayed on a telecommunications terminal, in particular a portable telephone, wherein, with said messages being made up of words themselves made up of characters, the method includes compiling two encoding tables, namely an “encoding table for compressing words”, causing each compressed word represented by its rank in the table to correspond to a “semi-compressed” word made up of a sequence of compressed characters corresponding to the word, and an “encoding table for compressing characters”, causing each compressed character represented by its rank in the table to correspond to a non-compressed character.
The present invention also provides a corresponding method of decompressing messages, wherein the method includes addressing two encoding tables respectively with compressed words and with compressed characters, the encoding tables being respectively an “encoding table for compressing words”, causing each compressed word represented by its rank in the table to correspond to a “semi-compressed” word made up of a sequence of compressed characters corresponding to the word, and an “encoding table for compressing characters”, causing each compressed character represented by its rank in the table to correspond to a non-compressed character.
The present invention also provides corresponding apparatus for decompressing messages, said apparatus essentially including a memory containing two encoding tables, namely an “encoding table for compressing words”, causing each compressed word represented by its rank in the table to correspond to a “semi-compressed” word made up of a sequence of compressed characters corresponding to the word, and an “encoding table for compressing characters”, causing each compressed character represented by its rank in the table to correspond to a non-compressed character, and means for addressing the two tables, respectively with compressed words and with compressed characters.
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Yeheskel Bar-Ness et al, “Word Based Data Compression Schemes 1”, May 8, 1989, Proceedings of the International Sysmposium on Circuits and Systems, Portland, May 8-11, 1989, vol. 1 of 3, pp. 300-308, Institute of Electrical and Electronics Engineers.
Alcatel Mobile Phones
Boudreau Leo
Mariam Daniel G.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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