Method and apparatus for coding and decoding digital image data using image quantization modification
First Claim
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1. An image coding apparatus that receives an input image per coding unit, which is obtained by dividing an original digital image into coding units, and codes the input image to obtain coded data, said apparatus comprising:
- subtraction means for providing a difference image between the input image per coding unit and a reference image generated from a coded image which has already been coded;
image transform means for receiving, as an input image to be transformed, one of the input image per coding unit and the difference image, and performing a prescribed transformation process to the input image to be transformed, thereby to obtain a transformed image;
quantization means for quantizing the transformed image by one of a prescribed quantization scale and a modified quantization scale which is given from a quantization scale decision means, thereby to obtain transformed and quantized coefficients;
coding means for coding the transformed and quantized coefficients to obtain coded data, and outputting the coded data;
local characteristic value calculation means for obtaining a complexity index value from the input image to be transformed and, using the complexity index value, calculating local characteristic values which are used for modification of the prescribed quantization scale;
control information set means for setting control information which is used for modification of the prescribed quantization scale; and
quantization scale decision means for modifying the prescribed quantization scale using the quantity of the coded data output from the coding means, the local characteristic values calculated by the local characteristic value calculation means, and the control information set by the control information set means, and outputting the modified quantization scale toward the quantization means.
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Abstract
An image coding method and apparatus for transforming and quantizing an image to produce transformed and quantized coefficients. The coefficients are coded and a complexity index value is obtained from the input image to calculate local characteristic values used to modify the quantization scale. In this manner, rate control is obtained on the basis of the local characteristics of the image, whereby the quality of the coded image and the precision of the rate control is improved.
100 Citations
20 Claims
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1. An image coding apparatus that receives an input image per coding unit, which is obtained by dividing an original digital image into coding units, and codes the input image to obtain coded data, said apparatus comprising:
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subtraction means for providing a difference image between the input image per coding unit and a reference image generated from a coded image which has already been coded; image transform means for receiving, as an input image to be transformed, one of the input image per coding unit and the difference image, and performing a prescribed transformation process to the input image to be transformed, thereby to obtain a transformed image; quantization means for quantizing the transformed image by one of a prescribed quantization scale and a modified quantization scale which is given from a quantization scale decision means, thereby to obtain transformed and quantized coefficients; coding means for coding the transformed and quantized coefficients to obtain coded data, and outputting the coded data; local characteristic value calculation means for obtaining a complexity index value from the input image to be transformed and, using the complexity index value, calculating local characteristic values which are used for modification of the prescribed quantization scale; control information set means for setting control information which is used for modification of the prescribed quantization scale; and quantization scale decision means for modifying the prescribed quantization scale using the quantity of the coded data output from the coding means, the local characteristic values calculated by the local characteristic value calculation means, and the control information set by the control information set means, and outputting the modified quantization scale toward the quantization means. - View Dependent Claims (2, 3, 4, 5, 6)
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7. An image decoding apparatus for decoding coded image data to obtain an image, comprising:
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variable-length decoding means for decoding coded image data to generate a transformed and quantized image, reference image information, and a modified quantization scale; inverse quantization means for performing inverse quantization to the transformed and quantized image using the modified quantization scale, thereby to obtain an inversely quantized image; inverse image transform means for performing inverse transform to the inversely quantized image, thereby to obtain an inversely transformed image; addition means for generating a decoded image using the inversely transformed image and a reference image which is obtained from image storage means described later; and image storage means for storing the decoded image for a prescribed period of time, generating a reference image from the stored decoded image and the reference image information output from the variable-length decoding means, and outputting the reference image to the addition means; wherein the coded image data is obtained from an image coding apparatus that receives an input image per coding unit, which is obtained by dividing an original digital image into coding units, and codes the input image to obtain coded data, said apparatus comprising subtraction means for providing a difference image between the input image per coding unit and a reference image generated from a coded image which has already been coded; image transform means for receiving, as an input image to be transformed, one of the input image per coding unit and the difference image, and performing a prescribed transformation process to the input image to be transformed, thereby to obtain a transformed image; quantization means for quantizing the transformed image by one of a prescribed quantization scale and a modified quantization scale which is given from a quantization scale decision means, thereby to obtain transformed and quantized coefficients; coding means for coding the transformed and quantized coefficients to obtain coded data, and outputting the coded data, local characteristic value calculation means for obtaining a complexity index value from the input image to be transformed and, using the complexity index value, calculating local characteristic values which are used for modification of the prescribed quantization scale; control information set means for setting control information which is used for modification of the prescribed quantization scale; and quantization scale decision means for modifying the prescribed quantization scale using the quantity of the coded data output from the coding means, the local characteristic values calculated by the local characteristic value calculation means, and the control information set by the control information set means, and outputting the modified quantization scale toward the quantization means.
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8. An image coding method wherein an input image per coding unit, which is obtained by dividing an original digital image into coding units, is coded to obtain coded data, said method comprising:
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subtraction step of providing a difference image between the input image per coding unit and a reference image generated from a coded image which has already been coded; image transform step of receiving, as an input image to be transformed, one of the input image per coding unit and the difference image, and performing a prescribed transformation process to the input image to be transformed, thereby to obtain a transformed image; quantization step of quantizing the transformed image by one of a prescribed quantization scale and a modified quantization scale which is decided in a quantization scale decision step, thereby to obtain transformed and quantized coefficients; coding step of coding the transformed and quantized coefficients to generate coded data; local characteristic value calculation step of obtaining a complexity index value from the input image to be transformed and, using the complexity index value, calculating local characteristic values which are used for modification of the prescribed quantization scale; control information set step of setting control information which is used for modification of the prescribed quantization scale; and quantization scale decision step of modifying the prescribed quantization scale using the quantity of the coded data generated in the coding step, the local characteristic values calculated in the local characteristic value calculation step, and the control information set in the control information set step, thereby to decide a modified quantization scale. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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15. A recording medium containing an image coding program for coding an input image per coding unit, which is obtained by dividing an original digital image into coding units, thereby to obtain coded data, said image coding program comprising:
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subtraction step of providing a difference image between the input image per coding unit and a reference image generated from a coded image which has already been coded; image transform step of receiving, as an input image to be transformed, one of the input image per coding unit and the difference image, and performing a prescribed transformation process to the input image to be transformed, thereby to obtain a transformed image; quantization step of quantizing the transformed image by one of a prescribed quantization scale and a modified quantization scale which is decided in a quantization scale decision step, thereby to obtain transformed and quantized coefficients; coding step of coding the transformed and quantized coefficients to generate coded data; local characteristic value calculation step of obtaining a complexity index value from the input image to be transformed and, using the complexity index value, calculating local characteristic values which are used for modification of the prescribed quantization scale; control information set step of setting control information which is used for modification of the prescribed quantization scale; and quantization scale decision step of modifying the prescribed quantization scale using the quantity of the coded data generated in the coding step, the local characteristic values calculated in the local characteristic value calculation step, and the control information set in the control information set step, thereby to decide a modified quantization scale. - View Dependent Claims (16, 17, 18, 19)
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20. A recording medium containing an image decoding program for decoding coded image data to obtain an image, said image decoding program comprising:
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variable-length decoding step of decoding coded image data to generate a transformed and quantized image, reference image information, and a modified quantization scale; inverse quantization step of performing inverse quantization to the transformed and quantized image using the modified quantization scale, thereby to obtain an inversely quantized image; inverse image transform step of performing inverse transform to the inversely quantized image, thereby to obtain an inversely transformed image; addition step of generating a decoded image using the inversely transformed image and a reference image which is generated in an image storage step; and image storage step of storing the decoded image for a prescribed period of time, and generating a reference image from the stored decoded image and the reference image information generated in the variable-length decoding step; wherein the coded image data is obtained from an image coding method wherein an input image per coding unit, which is obtained by dividing an original digital image into coding units, is coded to obtain coded data, said method comprising subtraction step of providing a difference image between the input image per coding unit and a reference image generated from a coded image which has already been coded; image transform step of receiving, as an input image to be transformed, one of the input image per coding unit and the difference image, and performing a prescribed transformation process to the input image to be transformed, thereby to obtain a transformed image; quantization step of quantizing the transformed image by one of a prescribed quantization scale and a modified quantization scale which is decided in a quantization scale decision step, thereby to obtain transformed and quantized coefficients; coding step of coding the transformed and quantized coefficients to generate coded data; local characteristic value calculation step of obtaining a complexity index value from the input image to be transformed and, using the complexity index value, calculating local characteristic values which are used for modification of the prescribed quantization scale; and quantization scale decision step of modifying prescribed quantization scale using the quantity of the coded data generated in the coding step, the local characteristic values calculated in the local characteristic value calculation step, and the control information set in the control information set step, thereby to decide a modified quantization scale.
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Specification