Fast DCT method and apparatus for digital video compression
First Claim
1. A method for performing a fast discrete cosine transform (DCT) on an image block composed of a matrix of pixels, comprising:
- calculating a block variance of an image block, said block variance indicating range of a block pixels;
determining a number of DCT coefficients to be calculated according to the block variance; and
calculating the value of DCT coefficients.
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Abstract
The present invention provides method and apparatus of a fast DCT implementation. DCT calculation is combined with quantization scales by a procedure of pre-processing. During DCT coefficient calculation, only non-zero coefficients are calculated. If pixel variance range is smaller than a first predetermined threshold, a predetermined lookup table is compared to decide the DCT coefficients. When a pixel variance range of a block pixels is within the second threshold, coupled with the quantization scales, the pre-processing determines the amount of non-zero DCT coefficients need to be calculated. Only a limited amount of LSB bits within a block is applied in the calculation of DCT coefficients. A previously saved pixel with equal or closest pixel value is used to replace the operation of current pixel'"'"'s multiplication.
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Citations
20 Claims
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1. A method for performing a fast discrete cosine transform (DCT) on an image block composed of a matrix of pixels, comprising:
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calculating a block variance of an image block, said block variance indicating range of a block pixels;
determining a number of DCT coefficients to be calculated according to the block variance; and
calculating the value of DCT coefficients. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method for determining DCT coefficients on an image block, comprising:
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comparing a variance range of block pixel differences to predetermined thresholds; and
using predetermined values to represent DCT coefficients if a variance range of block pixels is within a first threshold. - View Dependent Claims (11, 12)
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13. A compression circuit for calculating DCT coefficients of an image block, comprising:
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a calculating device for calculating a variance range of the image block;
a decision device coupled to the calculation device for discarding a number of DCT coefficients so that they don'"'"'t need to be calculated to spare times of calculation, and a DCT calculation device for performing DCT of those coefficients that need to be calculated. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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Specification