Method and system for estimating objective quality of compressed video data
First Claim
1. A method for evaluating the quality of encoded video data, the method comprising the steps of:
- decoding at least a substantial portion of said encoded video data to produce decompressed video data including a plurality of blocks;
performing a discrete cosine transform (DCT) on said decompressed video data to produce a set of DCT coefficients for at least one AC frequency band;
simultaneously, extracting quantization matrix data for the at least one AC frequency band and extracting a quantizer scale for each block of said decompressed video data;
estimating a variance of said DCT coefficients;
determining an average quantization error for each set of said DCT coefficients based on said variance, said quantization matrix, and said quantizer scale; and
, calculating a peak signal to noise ratio (PSNR) based on said average quantization error.
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Abstract
The present invention relates to a method and system for evaluating the quality of encoded video data without gaining access to the source data or the compressed video bitstream. The system is configured to decode compressed video data using an MPEG decoder to produce decompressed video data. The decoded data is analyzed to determine whether the decompressed video data is intra-coded. If so, a discrete cosine transform (DCT) is performed to produce a set of DCT coefficients for at least one AC frequency band in the decompressed video data. At the same time, quantization matrix data of a frame of the decompressed video data as well as a quantizer scale for each block of the decompressed video data are extracted. Thereafter, the variance of the converted DCT coefficients is obtained, and then an average quantization error for each set of said DCT coefficients is determined based on the variance, the quantization matrix, and the quantizer scale. Lastly, a peak signal to noise ratio (PSNR) is calculated based on the resultant average quantization error.
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Citations
27 Claims
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1. A method for evaluating the quality of encoded video data, the method comprising the steps of:
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decoding at least a substantial portion of said encoded video data to produce decompressed video data including a plurality of blocks;
performing a discrete cosine transform (DCT) on said decompressed video data to produce a set of DCT coefficients for at least one AC frequency band;
simultaneously, extracting quantization matrix data for the at least one AC frequency band and extracting a quantizer scale for each block of said decompressed video data;
estimating a variance of said DCT coefficients;
determining an average quantization error for each set of said DCT coefficients based on said variance, said quantization matrix, and said quantizer scale; and
,calculating a peak signal to noise ratio (PSNR) based on said average quantization error. - View Dependent Claims (2, 3, 4, 5, 6, 13)
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7. A method for evaluating the quality of encoded video data, the method comprising the steps of:
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at least partially decompressing said encoded video data in an MPEG decoder and outputting a decompressed video data including a plurality of blocks;
detecting an intra-coded picture in each block of said decompressed video data;
if detected, performing a discrete cosine transform (DCT) on said decompressed video data to produce a set of DCT coefficients for at least one AC frequency band;
extracting quantization matrix data for the at least one AC frequency band;
extracting a quantizer scale for each block of said decompressed video data;
estimating a variance of said DCT coefficients;
determining an average quantization error for each set of said DCT coefficients; and
,calculating a peak signal to noise ratio (PSNR) based on said average quantization error. - View Dependent Claims (8, 9, 10, 11, 12)
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14. An apparatus for evaluating the quality of encoded video data comprising:
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a decoder for decoding at least a substantial portion of said encoded video data to produce decoded video data including a plurality of blocks;
a discrete cosine transform (DCT) configured to transform said decompressed video data into a set of DCT coefficients for at least one AC frequency band;
an extractor for extracting quantization matrix data for the at least one AC frequency band and for extracting a quantizer scale for each block of said decompressed video data;
a collector for estimating a variance of said DCT coefficients;
a first calculator for determining an average quantization error for each set of said DCT coefficients based on said variance, said quantization matrix, and said quantizer scale; and
,a second calculator for determining a peak signal to noise ratio (PSNR) based on said average quantization error. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21)
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22. An apparatus for evaluating the quality of encoded video data comprising:
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a decoder configured to decode compressed variable-length Huffinan codes and for producing therefrom decoded data, and for extracting quantization matrix data and a quantizer scale for each block of said decoded video data;
an inverse quantizer configured to perform inverse-quantizing of the decoded data output from said decoder to produce a set of DCT coefficients;
an inverse DCT configured to transform values of pixels in blocks of signals output from said inverse quantizer to dequantize decoded data including difference data;
a motion compensation and adder for receiving reference data within the encoded video data and said difference data from said inverse DCT to form motion-compensated pictures therefrom;
a collector coupled to the output of said inverse quantizer for estimating a variance of said DCT coefficients;
a first calculator for determining an average quantization error for each set of said DCT coefficients based on said variance, said quantization matrix, and said quantizer scale; and
,a second calculator for determining a peak signal to noise ratio (PSNR) based on said average quantization error. - View Dependent Claims (23, 24)
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25. A system for evaluating the quality of encoded video data comprising:
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a memory for storing a computer-readable code; and
,a processor operatively coupled to said memory, said processor configured to;
decompress said encoded video data to produce a decompressed video data including a plurality of blocks;
detect an intra-coded picture in each block of said decompressed video data;
if detected, perform a discrete cosine transform (DCT) on said decompressed video data to produce a set of DCT coefficients for at least one AC frequency band;
extract quantization matrix data for the at least one AC frequency band;
extract a quantizer scale for each block of said decompressed video data;
estimate a variance of said DCT coefficients;
determine an average quantization error for each set of said DCT coefficients; and
,calculate a peak signal to noise ratio (PSNR) based on said average quantization error. - View Dependent Claims (26, 27)
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Specification