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US 6,553,142 B2Granted
Quantization table adjustment
AssigneeAvid Technology, Inc.
InventorEric C. Peters
Life of this patent
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Abstract
The method for adjusting quality during image capture includes computing a discrete cosine transform of a digital image to create DCT coefficients. A quantization table is generated that specifies frequency bands to be filtered and the DCT coefficients are digitized using the quantization table. It is preferred that the DCT coefficients be ordered in a zig-zag sequence to facilitate run-length encoding.
Claims24
A method for compressing image data, comprising:
- receiving the image data,
- transforming a block of the image data using a discrete cosine transform to obtain a matrix of coefficients, wherein each coefficient corresponds to a frequency in a range of frequencies having low frequencies and high frequencies;
- defining at least one quantization matrix, wherein the quantization matrix has a plurality of quantization values, wherein each quantization value corresponds to a coefficient in the matrix of coefficients, and wherein each quantization value corresponds to a frequency in the range of frequencies having low frequencies and high frequencies, wherein the quantization values are defined to obtain a desired amount of data from processing the matrix of coefficients, wherein the quantization values in different quantization matrices are such that for increased compression, a quantization value corresponding to at least one higher frequency is changed whereas quantization values corresponding to at least one lower frequency is unchanged;
- quantizing the coefficients for the block of the image data using the defined quantization matrix;
- and
- encoding the quantized coefficients to produce compressed image data.
3 more elements
An apparatus for compressing image data, comprising:
- means for transforming a block of the image data using a discrete cosine transform to obtain a matrix of coefficients, wherein each coefficient corresponds to a frequency in a range of frequencies having low frequencies and high frequencies;
- means for specifying at least one quantization matrix, wherein the quantization matrix has a plurality of quantization values, wherein each quantization value corresponds to a coefficient in the matrix of coefficients, and wherein each quantization value corresponds to a frequency in the range of frequencies having low frequencies and high frequencies, wherein the quantization values are defined to obtain a desired amount of data from processing the matrix of coefficients, wherein the quantization values in different quantization matrices are such that for increased compression, a quantization value corresponding to at least one higher frequency is changed whereas quantization values corresponding to at least one lower frequency is unchanged;
- a quantizer for quantizing the coefficients for the block of the image data using the defined quantization matrix;
- and
- an encoder for encoding the quantized coefficients to produce compressed image data.
2 more elements
Dependencies are inferred from the claim text.