Image processing apparatus and image processing method for performing error diffusion processing for each region of an image

An image processing method of performing error diffusion processing for each region of an image divided into a plurality of regions so that each region has an overlapping processing region, comprising the steps of:

• Holding, in first holding unit, quantization errors, which occurred in the error diffusion processing for a region different from a region of interest containing a pixel of interest;
• holding, in a second holding unit, quantization errors which occurred in the error diffusion processing for a pixel near the pixel of interest in the region of interest;
• a first determination of determining whether or not the pixel of interest exists at a first pixel position where it is necessary to reference the first error holding unit based on a position of the pixel of interest in the region of interest and an error diffusion matrix to be used in quantization;
• a second determination of determining whether or not the pixel interest exists at a second pixel position where it is necessary to write in the first error holding unit based on the position of the pixel of interest in the region of interest, the error diffusion matrix, and a position of the overlapping processing region in the region of interest;
• obtaining errors to be referred, wherein when the pixel of interest exists at the first pixel position, the errors are obtained from both the first and second error holding units, and when the pixel of interest does not exist at the first pixel position, the errors are obtained from only the second error holding unit;
• calculating an addition value from a diffusion error and a value of the pixel of interest, and quantizing the addition value to obtain a quantization value of the pixel of interest, wherein the diffusion error is calculated from the errors obtained in the obtaining step using the error diffusion matrix;
• calculating a quantization error for the pixel of interest from the quantization value and the addition value;
• and
• storing the quantization error for the pixel of interest, wherein when the pixel of interest does not exist at the second pixel position, the quantization error for the pixel of interest is stored in only the second error holding unit, and when the pixel of interest exists at the second pixel position, the quantization error for the pixel of interest is stored in both the first and second error holding units.

An image processing apparatus for performing error diffusion processing for each region of an image divided into a plurality of regions so that each region has an overlapping processing region, comprising:

• a first error holding unit constructed to hold a diffusion error to be diffused to a pixel of interest and calculated from at least one error which occurred in the error diffusion processing for a region different from a region of interest containing the pixel of interest;
• a second error holding unit constructed to hold a diffusion error to be diffused to the pixel of interest and calculated from at least one error which occurred in the error diffusion processing for at least one pixel near the pixel of interest in the region of interest;
• a first determining unit constructed to determine whether or not the pixel of interest exists at a first pixel position where it is necessary to reference the first error holding unit based on a position of the pixel of interest in the region of interest;
• a second determining unit constructed to determine whether or not the pixel of interest exists at a second pixel position where it is necessary to write in the first error holding unit based on the position of the pixel of interest in the region of interest, and a position of the overlapping processing region in the region of interest;
• an obtaining unit constructed to obtain at least one diffusion error to be referred, wherein when the pixel of interest exists at the first pixel position, diffusion errors are obtained from both the first and second error holding units, and when the pixel of interest does not exist at the first pixel position, a diffusion error is obtained from only the second error holding unit;
• a quantizing unit constructed to calculate an addition value from the at least one diffusion error obtained by the obtaining unit and a value of the pixel of interest, and quantize the addition value to obtain a quantization value of the pixel of interest;
• a calculating unit constructed to calculate diffusion errors, which are diffused from the pixel of interest to pixels near the pixel of interest, from a difference between the quantization value and the addition value using an error diffusion matrix;
• and
• a storing unit constructed to store the diffusion errors diffused from the pixel of interest, wherein when the pixel of interest does not exist at the second pixel position, the diffusion errors diffused from the pixel of interest are stored in only the second error holding unit, and when the pixel of interest exists at the second pixel position, the diffusion errors diffused from the pixel of interest are stored in both the first and second error holding units.