Image processing apparatus, image processing method and program

• US 10,650,294 B2
• Filed: 01/03/2017
• Issued: 05/12/2020
• 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
• Primary Examiner(s): Nguyen, Anh-Vinh T
• Application Number:
  US15/397,629
• Publication Number:
  US 20170116502A1
• Time in Patent Office: 1,225 Days
• Field of Search: None
• 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 which converts an input image into a halftone image using a threshold value matrix including a plurality of threshold values, the image processing apparatus comprising:

one or more circuits configured to cause the image processing apparatus to function as;

a target value obtaining unit configured to obtain a target value relating to a target tone for a predetermined region based on pixel values of respective pixels included in the predetermined region and the threshold values corresponding to the respective pixels of the threshold value matrix;

an evaluation value determination unit configured to determine evaluation values for respective pixels included in the predetermined region; and

an output value determination unit configured to determine an output value of at least one pixel included in the predetermined region in the halftone image according to the target value and the evaluation values for the predetermined region.

2. The image processing apparatus according to claim 1, wherein each of the evaluation values is calculated such that the magnitude of the evaluation value is higher as the magnitude of the pixel value is bigger or the magnitude of the corresponding threshold value is smaller.

3. The image processing apparatus according to claim 1, wherein the evaluation value determination unit calculates the evaluation value of a pixel of interest using the formula:

“

pixel value of the pixel of interest -α

(α

>

0) x threshold value corresponding to the pixel of interest”

.

4. The image processing apparatus according to claim 3, wherein the evaluation value determination unit sets a in accordance with a characteristic of the predetermined region or the input image.

5. The image processing apparatus according to claim 4, wherein the evaluation value determination unit sets the value of a to a value lower than 1 if the predetermined region or the input image has a characteristic representing an edge or a character.

6. The image processing apparatus according to claim 4, wherein the evaluation value determination unit sets the value of α

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

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

8. The image processing apparatus according to claim 7, wherein the target value obtaining 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 7, wherein the target value obtaining unit calculates, as the target value, a number of pixels of which the average value is greater than the threshold value among the threshold values corresponding to the predetermined region.

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

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

a dither processing unit configured to perform a dither process using the threshold values corresponding to the predetermined region by regarding, for each of the respective pixels included in the predetermined value, a pixel value as the average value; and

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

11. The image processing apparatus according to claim 1, wherein the output value determination unit determines the output value in the halftone image as a minimum value or a maximum value if a pixel included in the predetermined region has a minimum pixel value or a maximum pixel value in a range of pixel values of the input image data, independent of the evaluation value.

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

13. The image processing apparatus according to claim 1, wherein the output value determination unit determines 0 or 1 as the output value of each pixel in the predetermined region.

14. The image processing apparatus according to claim 13, wherein 0 as the output value indicates not allocating a dot and 1 as the output value indicates allocating a dot.

15. The image processing apparatus according to claim 1, wherein the target value obtaining unit calculates a number of dots to be allocated in the predetermined region as the target value.

16. The image processing apparatus according to claim 1, further comprising a determination unit configured to determine descending order of the evaluation values as priority order of preferentially arranging dots, for each pixel in the region,

wherein the output value determination unit is configured to arrange a dot as the output value for a pixel of which the priority order is smaller than the target value.

17. The image processing apparatus according to claim 1, further comprising:

wherein the evaluation value determination unit calculates a value related to a potential for a dot to be allocated as the evaluation value.

18. The image processing apparatus according to claim 1, wherein the halftone image that consists of the output value of each pixel is data outputtable by an image forming apparatus that forms an image on a recording medium, and the target value indicates the density that the image forming apparatus outputs to the recording medium.

19. The image processing apparatus according to claim 1, wherein a resolution of the input image is identical to a resolution of the halftone image.

20. The image processing apparatus according to claim 1, wherein the output value determination unit determines output values of the respective pixels included in the predetermined region based on the target value.

21. The image processing apparatus according to claim 1, wherein the output value determination unit converts the input image into the halftone image by arranging dots in the predetermined region, a number of the dots corresponding to the target value, and wherein positions of the dots arranged in the predetermined region are determined in accordance with the evaluation values of respective pixels included in the predetermined region.

22. 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 which converts an input image into a halftone image using a threshold value matrix including a plurality of threshold values, the image processing unit comprising:

one or more circuits configured to cause the image processing apparatus to function as;

a target value obtaining unit configured to obtain a target value relating to a target tone for a predetermined region based on pixel values of respective pixels included in the predetermined region and the threshold values corresponding to the respective pixels of the threshold value matrix;

an evaluation value determination unit configured to determine evaluation values for respective pixels included in the predetermined region; and

an output value determination unit configured to determine an output value of at least one pixel included in the predetermined region in the halftone image according to the target value and the evaluation values for the predetermined region.

23. An image processing method for performing an image process which converts an input image into a halftone image using a threshold value matrix including a plurality of threshold values, the method comprising:

obtaining a target value relating to a target tone for a predetermined region based on pixel values of respective pixels included in the predetermined region and the threshold values corresponding to the respective pixels of the threshold value matrix;

determining evaluation values for respective pixels included in the predetermined region; and

determining an output value of at least one pixel included in the predetermined region in the halftone image according to the target value and the evaluation values for the predetermined.

24. An image processing apparatus which converts an input image into a halftone image using a threshold value matrix including a plurality of threshold values, the image processing apparatus comprising:

one or more processors and at least one memory,

the at least one memory being coupled to the one or more processors and having stored thereon instructions executable by the one or more processors,

wherein the execution of the instructions causes the image processing apparatus to function as;

a target value obtaining unit configured to obtain a target value relating to a target tone for a predetermined region, based on pixel values of respective pixels included in the predetermined region and the threshold values corresponding to the respective pixels of the threshold value matrix;

an evaluation value determination unit configured to determine evaluation values for respective pixels included in the predetermined region; and

an output value determination unit configured to determine an output value of at least one pixel included in the predetermined region in the halftone image according to the target value and the evaluation values for the predetermined region.

25. The image processing apparatus according to claim 24,

wherein each of the evaluation values is calculated such that the magnitude of the evaluation value is higher as the magnitude of the pixel value is bigger or the magnitude of the corresponding threshold value is smaller.

26. The image processing apparatus according to claim 24, wherein the target value obtaining unit calculates the target value based on an average value acquired by averaging pixel values of pixels included in the predetermined region.

27. The image processing apparatus according to claim 24, wherein the threshold value matrix has a blue-noise characteristic and is a matrix having a size larger than the predetermined region.

28. The image processing apparatus according to claim 24, wherein the output value determination converting unit determines 0 or 1 as the output value of each pixel in the predetermined region.

29. The image processing apparatus according to claim 24, wherein the target value obtaining unit calculates a number of dots allocated in the predetermined region as the target value.

30. The image processing apparatus according to claim 24, wherein the evaluation value determination unit calculates the evaluation value of a pixel of interest in the predetermined region based on a difference between a pixel value of the pixel of interest and a threshold value corresponding to the target pixel.

31. The image processing apparatus according to claim 24, wherein the evaluation value determination unit obtains a group of threshold values corresponding to the predetermined region from the threshold matrix.