Size reduction method and device for compressed images
First Claim
1. A method of reducing the size of an input image to a target size by using a quality scaling factor to reduce image quality, wherein the size reduction is effected by a reduction factor estimated from the quality scaling factor and image statistics inherent to the input image, said method comprising the steps of:
- selecting a range of quality scaling factors based on the target size;
obtaining a range of reduction factors based on the selected range of quality scaling factors for determining a quality-size relationship;
computing an estimated quality scaling factor corresponding to the target size based on the quality-size relationship;
obtaining an estimated reduction factor based on the estimated quality scaling factor for providing a difference between the target size and the size reduction effected by the estimated reduction factor; and
refining the range of the quality scaling factors for reducing the difference until the difference falls within a predetermined limit.
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Accused Products
Abstract
A method and device for reducing a compressed image to a target size by reducing the quality of the image by a quality scaling factor. Image statistics inherent to the image are used to compute the size reduction as a function of the quality scaling factor. Using the relationship between the quality and the size of the image, an estimated quality scaling factor is obtained based on the target size in an iterative process until the size reduction corresponding to the estimated quality scaling factor is substantially equal to the target reduction.
41 Citations
19 Claims
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1. A method of reducing the size of an input image to a target size by using a quality scaling factor to reduce image quality, wherein the size reduction is effected by a reduction factor estimated from the quality scaling factor and image statistics inherent to the input image, said method comprising the steps of:
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selecting a range of quality scaling factors based on the target size;
obtaining a range of reduction factors based on the selected range of quality scaling factors for determining a quality-size relationship;
computing an estimated quality scaling factor corresponding to the target size based on the quality-size relationship;
obtaining an estimated reduction factor based on the estimated quality scaling factor for providing a difference between the target size and the size reduction effected by the estimated reduction factor; and
refining the range of the quality scaling factors for reducing the difference until the difference falls within a predetermined limit. - View Dependent Claims (2, 3, 4, 5)
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6. A device for reducing the size of an input image to a target size by using a quality scaling factor to reduce image quality, wherein the size reduction is effected by a reduction factor estimated from image statistics inherent to the input image, and wherein a range of quality scaling factors is selected based on the target size for size reduction estimation, said device comprising:
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a first computation means, responsive to the range of quality scaling factors, for providing a corresponding range of reduction factors based on the image statistics, said range of quality scaling factors and said corresponding range of reduction factors forming a quality-size relationship;
a second computation means, responsive to the quality-size relationship, for determining an estimated quality scaling factor corresponding to the target size, so as to allow the first computation means to compute an estimated reduction factor for providing a difference between the target size and the size reduction effected by the estimated reduction factor; and
a third computation means, responsive to the difference, for refining the range of the quality scaling factors, thereby changing the range of reduction factors, the quality-size relationship, and the estimated reduction factor, wherein said refining is repeated until the difference falls within a predetermined limit. - View Dependent Claims (7, 8, 9, 10)
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11. A method of modifying a quantization table for reducing the size of a compressed input image to an output image of a target size, wherein the input image is decoded into a partially decompressed image to provide quantized coefficients, which are quantized according to the quantization table, the quantized coefficients including zero and non-zero values, said method comprising the steps of:
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determining a quality-size relationship based on the size reduction from the input image to the target size;
determining an estimated scaling factor based on the quality-size relationship and image statistics inherent to the input image;
scaling the quantization table by the estimated scaling factor for providing a modified quantization table; and
scaling the non-zero coefficients based on the estimated scaling factor for recompressing the partially decompressed image into the output image. - View Dependent Claims (12, 13, 14)
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15. A method of modifying a quantization table for reducing the size of a compressed input image to an output image of a target size, wherein the input image is decoded into a partially decompressed image to provide quantized coefficients, which are quantized according to the quantization table, the quantized coefficients including zero and non-zero values, said method comprising the steps of:
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determining an estimated scaling factor based on the target size;
scaling the quantization table by the estimated scaling factor for providing a modified quantization table; and
scaling the non-zero coefficients based on the estimated scaling factor for recompressing the partially decompressed image into the output image, wherein the size reduction is related to quality of the output image, said method further comprising the steps of;
selecting a range of quality scaling factors based on the target size; and
obtaining a range of reduction factors based on the selected range of quality scaling factors and image statistics inherent to the input image for determining a quality-size relationship, so as to allow the estimated scaling factor to be determined based on the quality-size relationship;
obtaining an estimated size of the output image based on the estimated scaling factor for providing a difference between the target size and estimated size; and
refining the range of quality scaling factors for reducing the difference until the difference falls within a predetermined limit. - View Dependent Claims (16, 17, 18, 19)
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Specification