Implementation of a transform and of a subsequent quantization
First Claim
1. A method for implementing an approximation of a discrete cosine transform (DCT) and a quantization, which transform and which quantization are to be applied subsequently to digital data for compression of said digital data, said method comprising:
- simplifying a predetermined transform matrix to require less operations when applied to digital data;
approximating elements of said simplified transform matrix constituting irrational numbers by rational numbers;
extending a predetermined quantization to include said operations which were removed in said simplification of said predetermined transform matrix, which included operations are adjusted to compensate for said approximation of elements of said simplified transform matrix by rational numbers; and
employing said simplified transform matrix with said approximated elements and said extended quantization as basis for implementing said sequence of a transform and a quantization which are to be applied to digital data.
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Abstract
The invention relates to an approximation of a DCT and a quantization which are to be applied subsequently to digital data for compression of this digital data. In order to improve the transform, it is proposed to simplify a predetermined transform matrix to require less operations when applied to digital data. In addition, elements of the simplified transform matrix constituting irrational numbers are approximated by rational numbers. These measures are compensated by extending a predetermined quantization to include the operations which were removed in the simplification of the predetermined transform matrix. The included operations are further adjusted to compensate for the approximation of elements of the simplified transform matrix by rational numbers. If the simplified transform matrix and the extended quantization are used as basis for implementation, a fast transform with a good resulting quality can be achieved. An approximation of an IDCT employed in decompression of compressed digital data can be simplified correspondingly.
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Citations
30 Claims
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1. A method for implementing an approximation of a discrete cosine transform (DCT) and a quantization, which transform and which quantization are to be applied subsequently to digital data for compression of said digital data, said method comprising:
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simplifying a predetermined transform matrix to require less operations when applied to digital data;
approximating elements of said simplified transform matrix constituting irrational numbers by rational numbers;
extending a predetermined quantization to include said operations which were removed in said simplification of said predetermined transform matrix, which included operations are adjusted to compensate for said approximation of elements of said simplified transform matrix by rational numbers; and
employing said simplified transform matrix with said approximated elements and said extended quantization as basis for implementing said sequence of a transform and a quantization which are to be applied to digital data. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method for implementing a dequantization and an approximation of an inverse discrete cosine transform (IDCT), wherein for decompression of digital data said quantization is to be applied in sequence with said inverse transform to compressed digital data, said method comprising:
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simplifying a predetermined inverse transform matrix to require less operations when applied to digital data;
approximating elements of said simplified inverse transform matrix constituting irrational numbers by rational numbers;
extending a predetermined dequantization to include said operations which were removed in said simplification of said predetermined inverse transform matrix, which included operations are adjusted to compensate for said approximation of elements of said simplified inverse transform matrix by rational numbers; and
employing said extended dequantization and said simplified inverse transform matrix with said approximated elements as basis for implementing said sequence of a dequantization and an inverse transform which are to be applied to compressed digital data. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
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29. An encoder for compressing digital data comprising:
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a transformer approximating a discrete cosine transform (DCT) for transforming digital data by applying a simplified transform matrix to said digital data, which simplified transform matrix is obtained by simplifying a predetermined transform matrix to require less operations when applied to digital data, and in which simplified transform matrix elements constituting irrational numbers are approximated by rational numbers; and
a quantization means coupled to an output of said transformer for quantizing said transformed digital data with an extended quantization, which extended quantization is obtained from a predetermined quantization by including said operations which are removed in said simplification of said predetermined transform matrix, said operations being adjusted to compensate for said approximation of elements of said simplified transform matrix.
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30. A decoder for decompressing digital data compressed by a discrete cosine transform (DCT) or an approximation of a discrete cosine transform (DCT) and a subsequent quantization, said decoder comprising:
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a dequantization means for dequantizing compressed digital data with an extended dequantization; and
a transformer approximating an inverse discrete cosine transform (IDCT) coupled to an output of said dequantization means for transforming dequantized digital data by applying a simplified inverse transform matrix, which simplified inverse transform matrix is obtained by simplifying a predetermined inverse transform matrix to require less operations when applied to digital data, and in which simplified transform matrix elements constituting irrational numbers are approximated by rational numbers;
wherein said extended dequantization applied by said dequantization means is obtained from a predetermined dequantization by including said operations which are removed in said simplification of said predetermined inverse transform matrix, said operations being adjusted to compensate for said approximation of elements of said simplified inverse transform matrix.
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Specification