Extracting image features from MPEG-2 compressed stream

In this paper, we propose a new image feature extraction algorithm in the compression domain. To minimize the decompression process the proposed feature extraction algorithm executes only the parsing process to the compressed bit stream. Then, by just decoding dct_dc_size in the MPEG-2 bit stream, we can determine if there exists any abrupt brightness change between two DCT blocks. According to the Huffman table for the MPEG-encoder, as the difference of the DC values between two succeeding DCT blocks increases, it yields longer coded bits. That is, the length of the coded DC value is proportional to the brightness change between two succeeding DCT blocks. Therefore, one can detect an edge feature between DCT blocks by just decoding the information regarding the number of bits assigned to the difference of the DC values. To demonstrate the usefulness of the proposed feature extraction method, we apply the detected edge features to find scene changes in the MPEG-2 compressed bit stream.