Image analysis – Image enhancement or restoration – Edge or contour enhancement
Reexamination Certificate
1998-11-18
2002-07-09
Lee, Thomas D. (Department: 2724)
Image analysis
Image enhancement or restoration
Edge or contour enhancement
C358S001900
Reexamination Certificate
active
06418242
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to video compression, and more particularly to a method of efficient and reliable detection of error blocks in a DCT-based compressed video sequence.
One noticeable defect in video sequences that have been subjected to a DCT-based codec, such as MPEG-2 video compression, is the incorrect displaying of DCT blocks of data that actually belong to a different field, usually due to coding or buffer overrun errors.
Co-pending U.S. patent application Ser. No. 09/152,495 entitled “Picture Quality Measurement Using Blockiness”, filed Sep. 10, 1998 by Bozidar Janko and Steven Maurer, describes a method of detecting the amount of blockiness in an image. Vertical and/or horizontal edges are detected and cross-correlated with a grid having a kernel equal in size to the DCT block sizes used in the particular compression scheme used. The average magnitude of the accumulation buckets used for the cross-correlation is compared with the maximum accumulation value from one. of the buckets to determine the amount of blockiness. If incorrect codec coding or buffer overruns cause error blocks throughout the image, a general blockiness measurement is sufficient to detect their presence. However, a general blockiness measurement doesn't reliably detect small numbers of error blocks because their blockiness signature is often masked by the noise in the overall picture content. A single error block in an image, otherwise devoid of blockiness, is often not enough to cause the overall blockiness measure to exceed acceptable tolerances, even though the defect is easily and often annoyingly obvious to the human eye.
What is desired is a method of efficient and reliable detection of error blocks in a DCT-based compressed video sequence that more reliably detects small numbers of error blocks in images in the video sequence which would not otherwise be detected via an overall blockiness measure.
BRIEF SUMMARY OF THE INVENTION
Accordingly the present invention provides a method of efficient detection of error blocks in a DCT-based compressed video sequence by extracting edges with a periodicity equal to the DCT block kernel of the compression scheme being used, as detected by an overall blockiness measure. The extracted edge energies corresponding to the DCT block edges may be summed and compared with an overall threshold to determine if a particular block is an error block. Alternatively each edge energy may be tested against an individual edge energy threshold, and those blocks which have a specified number of edges, typically three, that exceed the threshold are determined to be error blocks. Either method may further be refined by subtracting from the edge energy the moving average of localized energy around the edge being measured to reduce false positives from spatially noisy areas.
The objects, advantages and other novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawing.
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M.R. Pickering, et al, “A Statistical Error Technique for Low Bit-Rate Video”, 1997, pp. 773-776, vol. Conf 12, IEEE, US.
Chung J. Kuo, et al, “Adaptive Postprocessor of Block Encloded Images”, IEEE Transactions on Circuits and Systems for Video Technology, Aug. 5, 1995, pp. 298-304, vol. 4, IEEE, New York, US.
Junseong Park, et al, “Recovery of Block-coded Images from Channel Errors”, Proceedings of the International Conference on Communications, May 23-26, 1993, pp. 396-400, vol. 1/3, IEEE, New York, US.
M.R. Pickering, et al, A Error Concealment Technique in the Spatial Frequency Domain:, Signal Processing, European Journal Devoted to the Methods and Applications of Signal Processing, Oct. 1, 1996, pp. 185-189, vol. 54, No. 2, Elsevier Science, B.V. Ansterdam.
Brinich Stephen
Gray Francis I.
Lee Thomas D.
Tektronix Inc.
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