Apparatus and methods for recompression of digital images
First Claim
Patent Images
1. A method of enabling an image-adaptive, perceptually-lossless and near-maximal image compression, including:
- compressing a first image giving rise to a second image;
implementing a measure of added artifactual edges along coding block boundaries, including;
computing a difference image between the first and second images;
defining a plurality of regions within said difference image, each of said plurality of regions comprising a plurality of image blocks;
within said region, computing for each boundary between two coding blocks a respective added-blockiness score indicating an extent of added artifactual edges along the respective boundary;
computing a region quality score for each of said plurality of regions, based on the added-blockiness scores computed for each boundary within the region, giving rise to a respective plurality of region quality scores; and
computing an image quality score for the second image based on one or more of said plurality of region quality scores; and
determining, based at least upon said image quality score, whether a perceptual quality criterion is met by said second image.
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Abstract
A system and method for generating a second reduced size digital image from a first digital image, the method including iteratively compressing the first digital image to an extent determined by a quality measure comprising at least a blockiness measure quantifying added artifactual edges along coding block boundaries of the second image and/or use of a quantization matrix generated by computing a weighted average of the quantization matrix of the first digital image and a scaled second quantization matrix.
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Citations
55 Claims
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1. A method of enabling an image-adaptive, perceptually-lossless and near-maximal image compression, including:
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compressing a first image giving rise to a second image; implementing a measure of added artifactual edges along coding block boundaries, including; computing a difference image between the first and second images; defining a plurality of regions within said difference image, each of said plurality of regions comprising a plurality of image blocks; within said region, computing for each boundary between two coding blocks a respective added-blockiness score indicating an extent of added artifactual edges along the respective boundary; computing a region quality score for each of said plurality of regions, based on the added-blockiness scores computed for each boundary within the region, giving rise to a respective plurality of region quality scores; and computing an image quality score for the second image based on one or more of said plurality of region quality scores; and determining, based at least upon said image quality score, whether a perceptual quality criterion is met by said second image. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 34)
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- 22. An image compressing method comprising iteratively compressing a first digital image into a second reduced size digital image to an extent determined by a plurality of quality measures including a local similarity measure quantifying local similarities between the first image and the second reduced size image and by-a texture change measure between the first image and the second reduced size image, wherein said plurality of quality measures are mutually normalized and said extent depends on a product, and wherein said first image is provisionally compressed using provisional compression parameters and if said product passes a first threshold then said provisional compression parameters are used for subsequent compression.
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30. A computerized method that iteratively compresses a first digital image into a second reduced size digital image to an extent determined by a texture change measure including:
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performing at least one initial compression using at least one initial compression parameter; defining a plurality of corresponding regions within the first digital image and the second reduced size digital image; evaluating said initial compression by computing, for each the corresponding regions, a region textural change measure between the first digital image and the second reduced size digital image; computing an image textural change measure using one or more of the region quality measures; determining whether the texture change measure falls within a textural change measure interval; and if said textural change measure falls within the textural change measure interval terminating the method, and otherwise, compressing further using a further compression parameter larger or smaller than said initial compression parameter if said textural change measure falls on one or another side of the textural change measure interval respectively. - View Dependent Claims (31)
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- 32. A computerized system that iteratively compresses a first digital image into a second reduced size digital image to an extent determined by a local similarity measure quantifying local similarities between the first image and the second reduced size image and by a texture change measure between the first image and the second reduced size image, wherein said plurality of quality measures are mutually normalized and said extent depends on a product, and wherein said first digital image is provisionally compressed using provisional compression parameters and if said product passes a first threshold then said provisional compression parameters are used for subsequent compression.
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35. A system for enabling an image-adaptive, perceptually-lossless and near-maximal image compression, the system having a processor configured to:
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compress a first image giving rise to a second image; implement a measure of added artifactual edges along coding block boundaries, including; compute a difference image between the first and second images; define a plurality of regions within said difference image, each of said plurality of regions comprising a plurality of image blocks; within said region, compute for each boundary between two coding blocks a respective added-blockiness score indicating an extent of added artifactual edges along the respective boundary; compute a region quality score for each of said plurality of regions, based on the added-blockiness scores computed for each boundary within the region, giving rise to a respective plurality of region quality scores; and compute an image quality score for the second image based on at least one of said plurality of region quality scores; and determine based at least upon said image quality score, whether a perceptual quality criterion is met by said second image. - View Dependent Claims (36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51)
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- 52. An image compressing system having a processor configured to iteratively compress a first digital image into a second reduced size digital image to an extent determined by a plurality of quality measures including a local similarity measure quantifying local similarities between the first image and the second reduced size image and a texture change measure between the first image and the second reduced size image, wherein said plurality of quality measures are mutually normalized and said extent depends on a product, and wherein said processor is configured to provisionally compress said first image using provisional compression parameters and if said product passes a first threshold then to use said provisional compression parameters for subsequent compression.
Specification