Method and system for estimating objective quality of compressed video data

A method for evaluating the quality of encoded video data, the method comprising the steps of:

• 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.

An apparatus for evaluating the quality of encoded video data comprising:

• 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.

An apparatus for evaluating the quality of encoded video data comprising:

• 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.

A system for evaluating the quality of encoded video data comprising:

• 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.