IMAGE PROCESSING APPARATUS, IMAGE PROCESSING METHOD AND PROGRAM

• US 20170116502A1
• Filed: 01/03/2017
• Published: 04/27/2017
• Est. Priority Date: 06/18/2014
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Kodama, Shigeo, Ishikawa, Hisashi
• Granted Patent: US 10,650,294 B2
• Time in Patent Office: Days
• CPC Class Codes: G06K 15/1822 Analysing the received data before processing
• CPC Class Codes: G06K 15/1877 with provisions for treating some of the print data differently
• CPC Class Codes: G06T 3/40 Scaling of whole images or parts thereof, e.g. expanding or contracting
• CPC Class Codes: H04N 1/405 Halftoning, i.e. converting the picture signal of a continuous-tone original into a corresponding signal showing only two levels
• CPC Class Codes: H04N 1/4051 producing a dispersed dots halftone pattern, the dots having substantially the same size different sizes H04N1/4057
• CPC Class Codes: H04N 1/4074 using histograms

Abstract

An image processing apparatus includes a target value calculation unit configured to calculate a target value to be output in a predetermined region in input image data based on pixel values of pixels included in the region, a distribution order determination unit configured to determine a distribution order of output values for distributing output values corresponding to the target value in the region based on a pixel value of each pixel included in the region and a threshold value in the threshold matrix corresponding to the pixel, and an output value determination unit configured to determine an output value of each pixel included in the region by allocating the target value to at least one pixel included in the region in the distribution order.

Claims

1. An image processing apparatus comprising:

a target value calculation unit configured to calculate a target value, to be output in a predetermined region in input image data, based on pixel values of pixels included in the region;

a holding unit configured to hold a threshold value matrix including a plurality of threshold values;

a distribution determination unit configured to determine a distribution of output values corresponding to the target value in the predetermined region based on a difference between a pixel value of each pixel representing the input image data and a threshold value in the threshold value matrix corresponding to the pixel for each pixel included in the region; and

an output value determination unit configured to determine an output value of each pixel included in the region by allocating an output value corresponding to the target value to at least one pixel included in the region in the distribution.

2. The image processing apparatus according to claim 1, wherein the distribution determination unit sorts evaluation values for pixel according to the differences to determine the distribution.

3. The image processing apparatus according to claim 2, wherein each of the evaluation values is calculated such that the magnitude of the evaluation value increases as the magnitude of the pixel value increases or the magnitude of the corresponding threshold value decreases.

4. The image processing apparatus according to claim 3, wherein the distribution determination unit calculates an evaluation value for a pixel included in the region based on a difference between a pixel value of the pixel and a threshold value corresponding to the pixel.

5. The image processing apparatus according to claim 3, wherein the distribution determination unit calculates an evaluation value for a pixel included in the region using the formula:

“

pixel value of the pixel−

α

(α

≧

0)×

threshold value corresponding to the pixel”

.

6. The image processing apparatus according to claim 1, wherein the target value calculation unit calculates the target value based on an average value acquired by averaging pixel values of pixels included in the region.

7. The image processing apparatus according to claim 1, wherein the target value calculation unit has

an average value calculation unit configured to calculate an average value of pixel values of pixels included in the region;

a dither processing unit configured to perform a dither process using the threshold value matrix by regarding a pixel value of each pixel included in the region as an average value; and

a totalization unit configured to calculate the target value by totalizing results of a dither process performed by the dither processing unit.

8. The image processing apparatus according to claim 6, wherein the target value calculation unit calculates the target value based on a result of a γ

correction performed on the average value.

9. The image processing apparatus according to claim 1, wherein the output value determination unit determines an output value as a minimum value or a maximum value if a pixel included in the region has a minimum pixel value or a maximum pixel value in a range of pixel values of the input image data, independent of it place in the distribution.

10. The image processing apparatus according t claim 5, wherein the distribution determination unit sets a value of α

in accordance with a characteristic of the region or the input image data.

11. The image processing apparatus according to claim 10, wherein the distribution determination unit sets the value of α

to a value lower than 1 if the region or the input image data has a characteristic representing an edge or a character.

12. The image processing apparatus according to claim 10, wherein the distribution determination unit sets the value of α

to a value higher than 1 if the region or the input image data has a characteristic representing a flat part.

13. The image processing apparatus according to claim 1, wherein the output value determination unit determines an output value of a pixel of interest in the region by comparing each of evaluation values for pixels included in the region and an evaluation value for the pixel of interest.

14. The image processing apparatus according to claim 1, wherein the distribution determination unit acquires a threshold value group corresponding to the region from a threshold value matrix held by the holding unit.

15. The image processing apparatus according to claim 14, wherein the threshold value matrix has a blue-noise characteristic and is a matrix having a size larger than the region.

16. A non-transitory storage medium storing a computer program which on execution by a computer causes the computer to function as an image processing apparatus comprising:

a target value calculation unit configured to calculate a target value, to be output in a predetermined region in input image data, based on pixel values of pixels included in the region;

a holding unit configured to hold a threshold value matrix including a plurality of threshold values;

a distribution determination unit configured to determine a distribution of output values corresponding to the target value in the predetermined region based on a difference between a pixel value of each pixel representing the input image data and a threshold value in the threshold value matrix corresponding to the pixel for each pixel included in the region; and

an output value determination unit configured to determine an output value of each pixel included in the region by allocating an output value corresponding to the target value to at least one pixel included in the region in the distribution.

17. An image processing method for performing an image process on input image data, the method comprising:

calculating a target value to be output in a predetermined region in input image data based on pixel values of pixels included in the region;

acquiring a threshold value group corresponding to the predetermined region from a threshold value matrix including a plurality of threshold values;

determining a distribution of an output value corresponding to the target value in the predetermined region based on a difference between a pixel value of each pixel representing the input image data and a threshold value corresponding to the pixel for each pixel included in the region; and

determining an output value of each pixel included in the region by allocating an output value corresponding to the target value to at least one pixel (where the number of pixels is determined based on the target value) included in the region in the distribution.