US 5,291,284 A · Predictive coding and decoding with error drift reduction

Abstract

A predictive coder, e.g., a hybrid DCT interframe predictive video decoder, reduces the tendency of long-term bias error in the decoded difference signal to accumulate in a predictor (7) by periodically alternating the polarity of the bias error relative to the contents of the predictor. Inverse discrete cosine transform (IDCT) stage (6) in a receiver is bracketed by switchable invertors (9a,9b) which, when operating, invert the signal into IDCT stage (6) and then reinvert the signal, plus error, out of IDCT stage (6), thereby inverting the error relative to the difference signal. Control means (10), e.g., a pseudo-random number generator, switches the invertors (9a,9b) in and out periodically such that, over several frames, each block spends an equal amount of time in "normal" and "inverted" modes.

Claims22

Dependent claims

A predictive decoder comprising means for supplying a difference signal, means for supplying a prediction signal, and means for combining the said two signals to form an output signal dependent thereon, the prediction signal being derived from the output signal so as to depend upon previous portions of the difference signal, characterised in that means are provided for periodically alternating the operation of the decoder between first and second states, in which the cumulative effect of any time-averaged bias present in the difference signal is, respectively, to increase and to deplete the prediction signal, the respective lengths of the periods spent in the first and second states being such as to reduce the tendency of such time-averaged bias error to accumulate in the prediction signal.

A digital signal processing device comprising:

means for producing an output signal, the means for producing an output signal being operative in a first state and a second state, the time-average of any error in said output signal being of opposite sign in said first and second states, respectively, and
means for alternating the device between the first state and the second state, whereby alternating the device periodically between said first and second states reduces the long-term average value of the error in said output signal.

Dependencies are inferred from the claim text.

Predictive coding and decoding with error drift reduction

Life of this patent

Predictive coding and decoding with error drift reduction

Life of this patent

Abstract

Claims22