Television – Bandwidth reduction system – Data rate reduction
Patent
1995-12-27
1998-09-29
Lee, Richard
Television
Bandwidth reduction system
Data rate reduction
348409, 348420, H04N 730
Patent
active
058152075
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method and circuits for differential coding and decoding.
BACKGROUND OF THE INVENTION
A method normally used for reducing the information to be transmitted is to carry out the difference between the signal in transit and its predicted one.
At this point the problem arises in that if the input signal is confined within a certain range of values, then the signal, obtained by carrying out the difference between input signal and predicted signal, has a double range.
Simple algorithms, capable of maintaining the differential signal within the range of the original signal, are known.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of differential coding and decoding which is capable of efficiently reducing the redundancy of the information to be transmitted.
In accordance with the invention the coding method is a method for coding a video signal comprising the steps of considering blocks of X rows and Y columns of said video signal, calculating the bidimensional Discrete Cosine Transform of said blocks, predicting the transform coefficients of the first column of each transformed block, carrying out a difference between the true value of each of said transform coefficients and the predicted value of each of said transform coefficients if said true value is different from zero, and characterized by predicting said transform coefficients of the first column of each transformed block using coefficients of further columns of said transformed block and coefficients of a preceding transformed block, coding said difference by associating more probable difference values to smaller numbers, thereby maintaining said numbers within the initial range of said true value, and coding the true value of said transform coefficient as such if said true value is equal to 0. A decoding circuit according to the invention comprises a circuit for coding a video signal comprising, means for considering blocks of X rows and Y columns of said video signal, means for calculating the bidimensional Discrete Cosine Transform of said blocks, means for predicting the transform coefficients of the first column of each transformed block, means for carrying out a difference between the true value of each of said transform coefficients and the predicted value of each of said transform coefficients if said true value is different from zero, characterized in that said means for predicting the transform coefficients of the first column of each transformed block uses coefficients of further columns of said transformed block and coefficients of a preceding transformed block, and said circuit further comprises means for coding said difference by associating more probable difference values to smaller numbers, thereby maintaining said numbers within the initial range of said true value, and means for coding the true value of said transform coefficient as such if said true value is equal to 0.
BRIEF DESCRIPTION OF THE DRAWING
The FIGURE is a block diagram of a circuit for coding/decoding signal according to the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
The invention will become more intelligible from the following description.
The differential coding is a special type of coding which, instead of coding directly an input signal, carries out the difference between this signal and a predicted signal of it. For the prediction of the input signal it is possible to use any type of predictor; in the simplest case the value encoded previously can be used as the prediction signal.
Assuming that the input signal values are comprised in the set (-range . . . , range -1), range being a positive integer, it results that the difference between this signal and its predicted one has a double range.
Therefore, the problems arises as to how the differential signal can be led within the original range.
The algorithm herein set forth is known from the literature and is the simplest method for maintaining the differential signal within the original range signa
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Cucchi Silvio
Lazzer Maurizio
ALCATEL N.V.
Lee Richard
Oliver Milton
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