Image processing method, program, storage medium, and apparatus for executing a quantization process of image data by error diffusion
First Claim
1. An image processing method for executing a quantization process of image data by error diffusion, using a computer to perform steps comprising:
- a step of calculating a diffusion error for a pixel of interest based on quantization errors, stored in a storing unit, of neighboring pixels of the pixel of interest;
a step of generating first image data by adding the calculated diffusion error to input image data of the pixel of interest;
a step of generating second image data by quantizing the first image data by comparing the first image data with a threshold value;
a step of generating third image data by dequantizing the second image data;
a quantization error calculation step of calculating a quantization error for each pixel on the basis of a difference between the first and third image data;
a storage step of storing the calculated quantization error for a predetermined number of pixels in the storage unit;
a counting step of counting a number of neighboring pixels of the pixel of interest having a quantization error with a predetermined sign based on sign bits of the calculated quantization error for neighboring pixels of the pixel of interest, wherein each sign bit indicates that the corresponding calculated quantization error is positive or negative; and
a control step of controlling the threshold value of the pixel of interest according to a count result in said counting step.
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Abstract
An image processing method for executing a quantization process of image data by error diffusion, executes a step of generating first image data by adding a quantization error to input image data, a step of generating second image data by quantizing the first image data by comparing the first image data with a predetermined threshold value, a step of generating third image data by dequantizing the second image data, a calculation step of calculating a quantization error for each pixel on the basis of the difference between the first and third image data, a storage step of storing information indicating a positive/negative sign of the calculated quantization error for a predetermined number of pixels in a storage unit, and a correction value generation step of generating a correction value used to correct at least one of the first image data and the threshold value on the basis of the information which is stored in the storage unit and indicates the positive/negative sign.
42 Citations
18 Claims
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1. An image processing method for executing a quantization process of image data by error diffusion, using a computer to perform steps comprising:
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a step of calculating a diffusion error for a pixel of interest based on quantization errors, stored in a storing unit, of neighboring pixels of the pixel of interest; a step of generating first image data by adding the calculated diffusion error to input image data of the pixel of interest; a step of generating second image data by quantizing the first image data by comparing the first image data with a threshold value; a step of generating third image data by dequantizing the second image data; a quantization error calculation step of calculating a quantization error for each pixel on the basis of a difference between the first and third image data; a storage step of storing the calculated quantization error for a predetermined number of pixels in the storage unit; a counting step of counting a number of neighboring pixels of the pixel of interest having a quantization error with a predetermined sign based on sign bits of the calculated quantization error for neighboring pixels of the pixel of interest, wherein each sign bit indicates that the corresponding calculated quantization error is positive or negative; and a control step of controlling the threshold value of the pixel of interest according to a count result in said counting step. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An image processing apparatus for executing a quantization process of image data by error diffusion, comprising:
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a storage unit for storing quantization errors for a predetermined number of pixels; a unit for calculating a diffusion error for a pixel of interest based on quantization errors, stored in the storing unit, of neighboring pixels of the pixel of interest; a unit for generating first image data by adding the calculated diffusion error to input image data to the pixel of interest; a unit for generating second image data by quantizing the first image data by comparing the first image data with a threshold value; a unit for generating third image data by dequantizing the second image data; a quantization error calculation unit for calculating a quantization error for each pixel on the basis of a difference between the first and third image data, wherein the calculated quantization error is stored in the storage unit; a counting unit for counting a number of neighboring pixels of interest having a quantization error with a predetermined sign based on sign bits of the calculated quantization error for neighboring pixels of the pixel of interest, wherein each sign bit indicates that the corresponding calculated quantization error is positive or negative; and a control unit for controlling the threshold value of the pixel of interest according to a count result from said counting unit. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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Specification