IMAGE PROCESSING APPARATUS AND IMAGE PROCESSING METHOD

• US 20110164829A1
• Filed: 12/10/2010
• Published: 07/07/2011
• Est. Priority Date: 01/06/2010
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Moribe, Shoei
• Granted Patent: US 8,391,624 B2
• Time in Patent Office: Days
• US Class Current: 382/275
• CPC Class Codes: H04N 1/4052 by error diffusion, i.e. transferring the binarising error to neighbouring dot decisions

Abstract

The value of a diffusing error for an interest pixel is added to image data of the interest pixel, and is calculated from error data occurred in quantization of pixels adjacent to the interest pixel. The image data, to which the value of the diffusing error is added, is quantized using a quantization threshold. Error data of the interest pixel is calculated from the result of the quantization and the image data to which the value of the diffusing error is added. Pixels which are adjacent to the interest pixel and have quantization results corresponding to the image data of the interest pixel are detected, and information between pixels is calculated based on differences between the image data and quantization results of adjacent pixels which fall within ranges corresponding to the detected adjacent pixels. The quantization threshold for the interest pixel is set based on the information between pixels.

Claims

1. An image processing apparatus for quantizing image data, comprising:

a corrector, configured to add a value of a diffusing error for a pixel of interest to input image data of the pixel of interest, wherein the value of the diffusing error is calculated from error data which are occurred in quantization of pixels adjacent to the pixel of interest;

a quantization section, configured to quantize the image data, to which the value of the diffusing error is added, using a quantization threshold value;

a calculator, configured to calculate error data of the pixel of interest from the result of the quantization and the image data to which the value of the diffusing error is added;

a detector, configured to detect pixels which are adjacent to the pixel of interest and have quantization results corresponding to the input image data of the pixel of interest; and

a setting section, configured to calculate information between pixels based on differences between input image data and quantization results of adjacent pixels which fall within ranges corresponding to the detected adjacent pixels, and to set the quantization threshold value for the pixel of interest based on the information between pixels.

2. The apparatus according to claim 1, wherein said detector determines whether a region in which the pixel of interest is present is a shadow region or a highlight region, and

wherein said detector detects adjacent pixels having quantization results indicating white pixels if it is determined that the pixel of interest falls within the shadow region, and detects adjacent pixels having quantization results indicating black pixels if it is determined that the pixel of interest falls within the highlight region.

3. The apparatus according to claim 1, wherein said setting section sets the quantization threshold value so as to obtain a distance between dots, which is nearly equal to a reciprocal of the input image data.

4. The apparatus according to claim 1, wherein said setting section sets the quantization threshold value for use in one of an error diffusion method and a minimized average error method.

5. A method of quantizing image data, comprising:

using a processor to perform the steps of;

adding a value of a diffusing error for a pixel of interest to input image data of the pixel of interest, wherein the value of the diffusing error is calculated from error data which are occurred in quantization of pixels adjacent to the pixel of interest;

quantizing the image data, to which the value of the diffusing error is added, using a quantization threshold value;

calculating error data of the pixel of interest from the result of the quantization and the image data to which the value of the diffusing error is added;

detecting pixels which are adjacent to the pixel of interest and have quantization results corresponding to the input image data of the pixel of interest;

calculating information between pixels based on differences between input image data and quantization results of adjacent pixels which fall within ranges corresponding to the detected adjacent pixels; and

setting the quantization threshold value for the pixel of interest based on the information between pixels.

6. A not-transitory computer readable medium storing a program for causing a computer to perform a method of quantizing image data, the method comprising the steps of:

adding a value of a diffusing error for a pixel of interest to input image data of the pixel of interest, wherein the value of the diffusing error is calculated from error data which are occurred in quantization of pixels adjacent to the pixel of interest;

quantizing the image data, to which the value of the diffusing error is added, using a quantization threshold value;

calculating error data of the pixel of interest from the result of the quantization and the image data to which the value of the diffusing error is added;

detecting pixels which are adjacent to the pixel of interest and have quantization results corresponding to the input image data of the pixel of interest;

calculating information between pixels based on differences between input image data and quantization results of adjacent pixels which fall within ranges corresponding to the detected adjacent pixels; and

setting the quantization threshold value for the pixel of interest based on the information between pixels.