Method apparatus and system for compressing data that wavelet decomposes by color plane and then divides by magnitude range non-dc terms between a scalar quantizer and a vector quantizer
First Claim
1. A method of compressing a digital image to obtain a compressed image data set for subsequent reconstruction, comprising the steps of:
- (i) determining if the digital image is a color image in RGB color space and converting any determined RGB color images to a less redundant color space;
(ii) performing a wavelet decomposition upon each of the color planes of the image in said less redundant color space to obtain a transform of DC and non-DC terms;
(iii) lossless coding the DC terms;
(iv) converting the transform to sign and magnitude format and selecting a division point comprising a pair of bit-planes which separate the non-DC terms into first and second ranges based upon absolute magnitudes, the first range comprising the values of the transform which are greater in magnitude than those values in the second range of the transform;
(v) employing a scalar quantizer to encode the values in the first range;
(vi) employing a vector quantizer to encode the values in the second range, the selection of chrominance vector components being based on Cr-Cb pairs at a given pixel location in transform space yielding two-dimensional vectors to reduce redundancy in color and scale/spatial location of the transform; and
(vii) coding the resulting data set with a lossless entropy encoder to obtain a compressed image data set.
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Abstract
An apparatus and method for image data compression performs a modified zero-tree coding on a range of image bit plane values from the largest to a defined smaller value, and a vector quantizer codes the remaining values and lossless coding is performed on the results of the two coding steps. The defined smaller value can be adjusted iteratively to meet a preselected compressed image size criterion or to meet a predefined level of image quality, as determined by any suitable metric. If the image to be compressed is in RGB color space, the apparatus converts the RGB image to a less redundant color space before commencing further processing.
165 Citations
27 Claims
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1. A method of compressing a digital image to obtain a compressed image data set for subsequent reconstruction, comprising the steps of:
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(i) determining if the digital image is a color image in RGB color space and converting any determined RGB color images to a less redundant color space;
(ii) performing a wavelet decomposition upon each of the color planes of the image in said less redundant color space to obtain a transform of DC and non-DC terms;
(iii) lossless coding the DC terms;
(iv) converting the transform to sign and magnitude format and selecting a division point comprising a pair of bit-planes which separate the non-DC terms into first and second ranges based upon absolute magnitudes, the first range comprising the values of the transform which are greater in magnitude than those values in the second range of the transform;
(v) employing a scalar quantizer to encode the values in the first range;
(vi) employing a vector quantizer to encode the values in the second range, the selection of chrominance vector components being based on Cr-Cb pairs at a given pixel location in transform space yielding two-dimensional vectors to reduce redundancy in color and scale/spatial location of the transform; and
(vii) coding the resulting data set with a lossless entropy encoder to obtain a compressed image data set. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. Apparatus for compressing a digital image to obtain a compressed image data set for subsequent reconstruction, comprising:
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means to detect and convert digital image from RGB colour space to a less redundant color space;
means to perform a wavelet decomposition of each color plane of said image in said less redundant color space to obtain a transform of DC and non-DC terms;
means to losslessly encode said DC terms;
means to convert said transform to a sign and magnitude format and to select a division point comprising a pair of bit planes which separate the non-DC terms into first and second ranges, based upon absolute magnitudes, the first range comprising values of the transform which are greater in magnitude than those in the second range of the transform;
scalar quantizer means to encode the values in said first range;
vector quantizer means to encode the values in said second range and to produce two dimensional vectors, the selection of chrominance vector components being based on Cr-Cb pairs at a given pixel location in transform space to reduce redundancy in color and scale/spatial location of the transform; and
means to losslessly encode the resulting data set to obtain a compressed image data set.
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27. An article of manufacture comprising a computer usable medium having computer readable program code means embodied therein for implementing a digital image compression apparatus, the computer readable program code means in said article of manufacture comprising:
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computer readable program code for causing said computer to detect and convert digital image data from RGB color space to a less redundant color space;
computer readable program code means for causing said computer to perform a wavelet decomposition of each color plane of said image in said less redundant color space to obtain a transform of DC and non-DC terms;
computer readable program code means for causing said computer to losslessly encode said DC terms;
computer readable programs code means for causing said computer to convert said transform to a sign and magnitude format and to select a division point comprising a pair of bit planes which separate the non-DC terms into first and second ranges, based upon absolute magnitudes, the first range comprising values of the transform which are greater in magnitude than those in the second range of the transform;
computer readable program code means for causing said computer to perform a scalar quantization to encode the values in said first range;
computer readable program code means for causing said computer to perform a vector quantization to encode the values in said second range and to produce two dimensional vectors, the selection of chrominance vector components being based on Cr-Cb pairs a given pixel location in transform space to reduce redundancy in color and scale/spatial location of the transform; and
computer readable program code means for causing said computer to losslessly encode the resulting data set to obtain a compressed image data set.
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Specification