Fast DCT domain downsampling and inverse motion compensation
First Claim
1. A method for downsampling image information in the compressed domain, where such information has been compressed in accordance with a discrete cosine transform (DCT) based compression scheme, the method comprising the steps of:
- Huffman decoding a compressed bitstream to extract a plurality of N×
N DCT-based data blocks;
processing n of said data blocks in accordance with at least one sampling matrix to extract a single N×
N DCT-based data block, wherein n is determined by a desired downsampling factor, and wherein said single data block is a determined average of said N data blocks.
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Abstract
Downsampling and inverse motion compensation are performed on compressed domain representations for video. By directly manipulating the compressed domain representation instead of the spatial domain representation, computational complexity is significantly reduced. For downsampling, the compressed stream is processed in the compressed (DCT) domain without explicit decompression and spatial domain downsampling so that the resulting compressed stream corresponds to a scaled down image, ensuring that the resulting compressed stream conforms to the standard syntax of 8×8 DCT matrices. For typical data sets, this approach of downsampling in the compressed domain results in computation savings around 80% compared with traditional spatial domain methods for downsampling from compressed data. For inverse motion compensation, motion compensated compressed video is converted into a sequence of DCT domain blocks corresponding to the spatial domain blocks in the current picture alone. By performing inverse motion compensation directly in the compressed domain, the reduction in computation complexity is around 68% compared with traditional spatial domain methods for inverse motion compensation from compressed data. The techniques for downsampling and inverse motion compensation can be used in a variety of applications, such as multipoint video conferencing and video editing.
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Citations
30 Claims
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1. A method for downsampling image information in the compressed domain, where such information has been compressed in accordance with a discrete cosine transform (DCT) based compression scheme, the method comprising the steps of:
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Huffman decoding a compressed bitstream to extract a plurality of N×
N DCT-based data blocks;processing n of said data blocks in accordance with at least one sampling matrix to extract a single N×
N DCT-based data block, wherein n is determined by a desired downsampling factor, and wherein said single data block is a determined average of said N data blocks. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for achieving inverse motion compensation in the compressed domain, where such information has been compressed in accordance with a discrete cosine transform (DCT) based compression scheme, the method comprising the steps of:
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Huffman decoding a compressed bitstream to extract a plurality of N×
N DCT-based data blocks defining a picture T-1, and to extract a motion vector h,w;processing n of said data blocks in accordance with at least one sampling matrix and with said motion vector to produce a single N×
N DCT-based data block corresponding to a picture T, wherein n is used to define a region occupied by said picture T-1, and wherein said single data block is a combination of a data block consisting of a determined average of said n data blocks. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. An apparatus for downsampling image information in the compressed domain, where such information has been compressed in accordance with a discrete cosine transform (DCT) based compression scheme, the apparatus comprising:
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a Huffman decoder for decoding a compressed bitstream to extract a plurality of N×
N DCT-based data blocks;a processor for processing n of said data blocks in accordance with at least one sampling matrix to produce a single N×
N DCT-based data block, wherein n is determined by a desired downsampling factor, and wherein said single data block is a determined average of said n data blocks. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23)
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24. An apparatus for achieving inverse motion compensation in the compressed domain, where such information has been compressed in accordance with a discrete cosine transform (DCT) based compression scheme, the apparatus comprising:
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a Huffman decoder for decoding a compressed bitstream to produce a plurality of N×
N DCT-based data blocks defining a picture T-1 and to produce a motion vector h,w;a processor processing n of said data blocks in accordance with at least one sampling matrix and with said motion vector to produce a single N×
N DCT-based data block corresponding to a frame T, wherein n is used to define a region occupied by said frame T-1, and wherein said single data block is a combination of a data block consisting of a determined average of said n data blocks. - View Dependent Claims (25, 26, 27, 28, 29, 30)
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Specification