Television – Monitoring – testing – or measuring – Transmission path testing
Patent
1996-01-18
1998-04-28
Peng, John K.
Television
Monitoring, testing, or measuring
Transmission path testing
348402, 348403, 348407, 348420, 348616, H04N 7133
Patent
active
057451699
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to detecting errors in signals representing video images.
2. Related Art
In addition to the broadcasting and storage of full bandwidth video signals, interest has also developed in techniques for reducing the bandwidth requirement for the transmission or storage of a video signal. These techniques facilitate, amongst other things, two-way transmission of video signals, leading to the development of affordable video conferencing facilities and video telephones.
A problem with compressing video data for transmission over limited bandwidth transmission paths, is that the data becomes more susceptible to the presence of transmission errors. The nature of the transmission path will be such that errors usually cannot be prevented and in order to improve the overall result of transmitted images, it would be preferable to identify the presence of errors, and their locations within the video image and, where possible, take action to conceal these errors.
One method for detecting errors comprises including an error correction code as an overhead. Cyclic redundancy codes are widely used for error detection at the expense of a small overhead in the transmitted signal.
If the error correction code is corrupted during transmission, this is detected at a receiver and the corrupted data replaced, for instance as described in U.S. Pat. No. 5,150,210.
SUMMARY OF THE INVENTION
The present invention seeks to provide an improved method and apparatus for detecting the presence of errors in a video signal.
According to a first aspect of the present invention, there is provided a method of detecting an error in a signal representing a video image, comprising:
receiving blocks of frequency related coefficients representing respective blocks in the video image; and
analysing the statistical distribution of said coefficients within a block to detect the presence of corrupted data.
In a preferred embodiment, said analysing step involves calculating the variance of said coefficients in a block. Variance is determined by calculating the difference between actual coefficient values and the mean value, forming the square of said difference and summing said squares, i.e. ##EQU1## where .sigma.=variance x.sub.i =value of the ith coefficient
The variance may be compared against a predetermined threshold and an error identified if the variance is greater than said threshold. Alternatively or additionally, the variance values for the blocks of a frame may be stored and the variance for a block under consideration may be compared with the variance of the block in a previous frame that is similarly positioned and/or for the surrounding blocks of the previous frame. A mean variance value may be calculated for the blocks of the previous frame and an error detected if the variance value under consideration is significantly larger or significantly smaller than the mean value for the previous frame.
If the transmission coding scheme employs frequency related coefficients which represent the actual values of the pixels within a block, for example the video signal is intraframe coded using DCT coefficients only, the mathematical distribution of the transmitted coefficients may be directly analysed. However the coding scheme employed might not result in frequency related coefficients representing the actual value of the pixels. For instance, if the transmitted signal represents the difference between the current frame and an earlier frame, the actual pixel values, and hence the mathematical distribution of the resulting frequency coefficients, cannot be obtained without first decompressing the received signal to produce the actual pixel values, and then dividing the signal into blocks and transforming the signal into the frequency domain to produce the frequency related coefficients.
In a preferred embodiment, action is taken to conceal a block if an error is identified. This may involve the substitution of the detected block by a similarly positioned block in a pre
REFERENCES:
patent: 4442454 (1984-04-01), Powell
patent: 4555729 (1985-11-01), Driessen
patent: 4807033 (1989-02-01), Keesen et al.
patent: 4897724 (1990-01-01), Veldhuis
patent: 5079631 (1992-01-01), Lhuillier et al.
patent: 5150210 (1992-09-01), Hoshi et al.
patent: 5228028 (1993-07-01), Cucchi et al.
patent: 5243428 (1993-09-01), Challapali et al.
Jeng et al, "Concealment of Bit Error and Cell Loss in Inter-Frame Coded Video Transmission", Internatiional Conference on Communication 91, vol. 1, 23 Jun. 1991, Denver, CO., pp. 496-500.
Patent Abstract of Japan, vol. 16, No.288 (E-1223) Jun. 25, 1992 & JP-A-04 072 985 (Toshiba Corporation.) 6 Mar. 1992.
Patent Abstracts of Japan, vol. 15, No. 261 (E-1085) 3 Jul. 1991 & JP-A-03 085 820 (Matsushita Electric Industrial Co., Ktd.) 11 Apr. 1991.
"An Error Concealment Method Agains Transmission Error in DCT Coding", Saito et al, Picture Coding Symposium, Sep. 1991, Tokyo, Japan, pp. 185-188.
"Selective Recovery of Video Packet Loss Using Error Concealment", Wada, IEEE Journal On Selected Areas in Communications, vol. 7, No. 5, Jun. 1989, pp. 807-814.
"Partial Correction of transmission Errors in Walsh Transform Image Without Recourse to Error Correction Coding", Wong et al, Electronics Letters, Apr. 1978, three pages.
"Predictable Sample Error Detector and a Planar Prediction Corrector for Removal of Isolated Transmission Errors in Walsh-Hadamard Transformed Pictures", Fenwich et al, Electronics Letters, Jul. 1977, 3 pages.
"Channel Error Recovery for Transform image Coding", Mitchell et al, IEEE Transaction On Communications, vol. Comm-29, No. 12, Dec. 1981, pp. 1754-1762.
"Video Compression Makes Big Gains", Ang et al, IEEE Spectrum, Oct. 1991, pp. 16-19.
"Partial Correction of Transmission Errors in D.P.C.M. Without Recourse to Error Correction Coding", Steele et al, Electronics Letters, Jun. 1977, pp. 351-353.
"Enhancement of PCM and DPCM Images Corrupted by Transmission Errors", Nigan et al, IEEE Transactions On Communications, vol.-Com-30, No. 1, Jan. 1982, pp. 257-264.
Gunby Stephen Richard
Murphy Angela Ruth
British Telecommunications public limited company
Murrell Jeffrey S.
Peng John K.
LandOfFree
Detecting errors in video images does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Detecting errors in video images, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Detecting errors in video images will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1537367