Compression method

Abstract: The invention is directed to a substantial improvement that allows to further reduce the information transmitted in the variable length encoding of numerical data blocks with encoding of single values and string lengths of consecutive values ("run length"). Advantageously it is not transmitted a particular more recurrent value, when it appears as last element in a string of this parti­ cular value preceded by a "run length" and followed by another "run length" or by a data block end ("data delimiter", DD). When the above mentioned string of this particular value, being in the same above mentioned condition, has a unitery length, this last sole value is not transmitted; in the more general case in which N values of these consecutive values are preceded by a "run length" and followed by another "run length" or by a data block end, N-1 values are transmitted.

Description: Description of the invention The present invention refers to a system for reducing the information transmitted by means of a variable length encoding of numerical data blocks with encoding of single values and string lengths of consecutive values defined as "run lengths". Without limiting in any manner and with the sole aim of example, it shall be assumed in the following that the more recurrent values held in the numerical sequences to be transmitted are in the order the zero numbers (0), the one numbers (1) (both positive and negative numbers), and then the other values appearing with decreasing frequency. An information transmission technics (T1), is known in which same values are singularly transmitted ( for example the numbers different from zero) and symbols representing string lengths having at least a particular recurrent value (for example the zero). For example, it is well-known that when a message of the following type must be transmitted: Total numbers to be transmitted = 46 The message is encoded as follows: Total symbols transmitted = 26 where Rn represents n consecutive zeros and the block end symbol (DD) allows to avoid the transmission of the final zeros. For further reducing the symbol numbers for each block to be transmitted, it was proposed (for example in the patent US-4.698.672) (T2) to distinguish the "run length" in two classes: the first class (An) represents all possible lengths of consecutive zeros (more recurrent values) followed by another sufficiently recurrent value (for example the number one positive or negative in sign) including, therefore, in a sole symbol the information related to the number of present zeros, followed by a number one (excepting the sign); the second class (Bn) represents all possible lengths of consecutive zeros followed by other less recurrent values. Then the message M2 is transmitted as follows: Total symbols transmitted = 20 This system includes surely some advantages, but it shows often other drawbacks, among which it is only indicated that, being compelled to differentiate the "run length" of type Bn (usual) from the ones of type An (now introduced, that hold implicitly the information of the following number) with one another, it is necessary to increase the symbol words of the encoding alphabet (translation of the symbol into bits), that must be available. Now the object of the present invention (T3) is to provide a system that does not show the drawbacks of the well-known technics and by which, in particular, it is possible to reduce the symbols to be transmitted in each block, and no problems of any other type are introduced. The system according to the invention is characterized in that all strings of N consecutive numbers, equal to a sufficiently recurrent value (for example the positive number one) preceded by a "run length" of "classic" type (for example the Rn of the message M2) and followed by another "run length" or by a block end symbol, are transmitted as they were made-up of N-1 numbers. According to a feature of the invention, when N=1, no value is transmitted. It is necessary to underline that this does not cause a data loss, as the message user posses all information necessary for the easy reconstruction of the original transmitted sequence. The message M2, indicated again hereunder, is now transmitted as follows: Total symbols transmitted = 22 As it can be noticed comparing M4 with M2, the convention has e.g. been adopted of transmitting no number one (positive) when it is isolated between two "run lengths" (cases a and b) or when it is the last number of a string included between two "run lengths" (case c), and also when it is the last number of a string preceded by a "run length" and followed by the block end symbol (case d). According to the well-known technics T1, the message M1 of the above mentioned example, made-up of 46 numbers, is transmitted by 26 symbols (M2) instead of 20 (M3) of the successive well-known technics T2 (patent US-4.689.672), while, according to the system forming the object of the present invention (T3), 22 symbols are necessary (M4). Generally, as it can be seen from this simple example, according to the invention (T3), more symbols are necessary for each block in comparision with the former well-known technics (T2): but the important matter is the translation of transmitted symbols into bit sequence. In fact the former well-known technics (T2) shows the necessity of increasing the symbol words of the encoding alphabet for being able to differentiate the "run length" of type Bn (usual type) from the ones of type An (introduced for transmitting implicitly the information onto the number following the "run length") among one another, it causes a deterioration of the translation of the transmitted symbols in bit sequence. The system according to the invention does not offer particular disadvantages for its hardware implementation, for which it is sufficient to introduce only few additional combinatory and sequential logic elements into the traditional processor, that "groups" the zeros for calculating the "run lengths".

Claims: A method of reducing the information transmitted in variable length encoding of numerical data blocks with encoding of single values and string lengths of consecutive values defined as "run lengths", characterised in that the transmission of the last recurrent value in a string of recurrent values is eliminated when said string of recurrent values is preceded by a "run length" and followed by another "run length" or by a block end symbol. The method of claim 1, wherein the string of revurrent values is not transmitted when it comprises a string of one value.

Inventors: RONCHETTI LUIGI, STROPPIANA MARIO, RONCHETTI, LUIGI, STROPPIANA, MARIO
Applicants: ALCATEL ITALIA, ALCATEL ITALIA SOCIETA PER AZIONI
Application year: 1990
Main classification: H03M7
IPC codes: H03M7, G06T9