Device and method for encoding digital image
First Claim
1. A digital image encoding device comprising:
- conversion means for converting digital image data into a coefficient based on a spatial frequency;
quantization means for quantizing the coefficient obtained by said conversion means; and
coefficient bit modeling means for carrying out coefficient bit modeling by using said coefficient quantized by said quantization means, wherein said digital image data is divided into a plurality of subbands in said conversion means, said coefficient bit modeling means comprises;
code block division means for dividing each of said subbands into a plurality of code blocks;
bit plane decomposition means for decomposing each of coefficients of said code blocks obtained by said code block division means into a plurality of bit planes for each bit weight;
subbit plane decomposition means for decomposing each of said bit planes obtained by said bit plane decomposition means into a plurality of subbit planes based on usefulness; and
predetermined data generation means for generating predetermined data in accordance with said subbit planes obtained by said subbit plane decomposition means, and said coefficient bit modeling means comprises requantization means for requantizing a predetermined subbit plane among said subbit planes obtained by said subbit plane decomposition means and passing data after said requantization to said predetermined data generation means.
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Abstract
There is provided a digital image encoding device which can enhance image compression performance while maintaining an image quality. When coefficient bits are decomposed/aligned in four encoded paths for each context by a procedure called coefficient bit modeling of a JPEG 2000 encoding system, if an appearance frequency of “1” is low in subbit plane coefficients of a clean-up path of a low-order bit plane n (bit plane n is lower in order than bit plane np represented by threshold value np), coefficients of subbit planes of this clean-up path are all reset to “0.” Thus, a run length used when a symbol and a context are generated is made longer and, as a result, the amount of codes after arithmetic encoding at a subsequent stage is reduced while an image quality deterioration is suppressed.
28 Citations
18 Claims
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1. A digital image encoding device comprising:
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conversion means for converting digital image data into a coefficient based on a spatial frequency;
quantization means for quantizing the coefficient obtained by said conversion means; and
coefficient bit modeling means for carrying out coefficient bit modeling by using said coefficient quantized by said quantization means, wherein said digital image data is divided into a plurality of subbands in said conversion means, said coefficient bit modeling means comprises;
code block division means for dividing each of said subbands into a plurality of code blocks;
bit plane decomposition means for decomposing each of coefficients of said code blocks obtained by said code block division means into a plurality of bit planes for each bit weight;
subbit plane decomposition means for decomposing each of said bit planes obtained by said bit plane decomposition means into a plurality of subbit planes based on usefulness; and
predetermined data generation means for generating predetermined data in accordance with said subbit planes obtained by said subbit plane decomposition means, and said coefficient bit modeling means comprises requantization means for requantizing a predetermined subbit plane among said subbit planes obtained by said subbit plane decomposition means and passing data after said requantization to said predetermined data generation means. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A digital image encoding method comprises:
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conversion step of converting digital image data into a coefficient based on a spatial frequency;
quantization step of quantizing said coefficient obtained by said conversion step; and
coefficient bit modeling step of carrying out coefficient bit modeling by using said coefficient quantized by said quantization step, wherein said digital image data is divided into a plurality of subbands in said conversion step, said coefficient bit modeling step comprises;
code block division step of dividing each of said subbands into a plurality of code blocks;
bit plane decomposition step of decomposing each of coefficients of said code blocks obtained by said code block division means into a plurality of bit planes for each bit weight;
subbit plane decomposition step of decomposing each of said bit planes obtained by said bit plane decomposition step into a plurality of subbit planes based on usefulness; and
predetermined data generation step of generating predetermined data in accordance with said subbit planes obtained by said subbit plane decomposition step, and said coefficient bit modeling step comprises requantization step of requantizing a predetermined subbit plane among said subbit planes obtained by said subbit plane decomposition step and passing data after said requantization to said predetermined data generation step. - View Dependent Claims (8, 9, 10, 11, 12)
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13. A program for causing a computer to perform a digital image encoding method, said method comprising:
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conversion step of converting digital image data into a coefficient based on a spatial frequency;
quantization step of quantizing said coefficient obtained by said conversion step; and
coefficient bit modeling step of carrying out coefficient bit modeling by using said coefficient quantized by said quantization step, wherein said digital image data is divided into a plurality of subbands in said conversion step, said coefficient bit modeling step comprises;
code block division step of dividing each of said subbands into a plurality of code blocks;
bit plane decomposition step of decomposing each of coefficients of said code blocks obtained by said code block division means into a plurality of bit planes for each bit weight;
subbit plane decomposition step of decomposing each of said bit planes obtained by said bit plane decomposition step into a plurality of subbit planes based on usefulness; and
predetermined data generation step of generating predetermined data in accordance with said subbit planes obtained by said subbit plane decomposition step, and said coefficient bit modeling step includes requantization step of requantizing a predetermined subbit plane among said subbit planes obtained by said subbit plane decomposition step and passing data after said requantization to said predetermined data generation step. - View Dependent Claims (14, 15, 16, 17, 18)
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Specification