Image processing device, image processing method, and recording medium storing image processing program

• US 20020028027A1
• Filed: 09/05/2001
• Published: 03/07/2002
• Est. Priority Date: 09/07/2000
• Status: Active Grant

• Current Assignee: Fuji Xerox Company Limited (Xerox Holdings Corp.)
• Original Assignee: Fuji Xerox Company Limited (Xerox Holdings Corp.)
• Inventors: Koyama, Toshiya
• Granted Patent: US 7,016,552 B2
• Time in Patent Office: Days
• US Class Current: 382/289
• CPC Class Codes: G06F 17/145 Square transforms, e.g. Hadamard, Walsh, Haar, Hough, Slant transforms
• CPC Class Codes: G06V 30/1478 of characters or characters lines

Abstract

A Hough transform unit executes Hough transform to HIGH pixels of outline binary image data inputted thereto, and stores the calculation result in a Hough space data storage. A Hough space data calculating/projecting unit sequentially reads out data stored in the Hough space data storage, executes a specific calculation, and thereafter stores the calculation result sequentially in a calculated projection data storage. An angle detector sequentially reads out calculated frequency data stored in the calculated projection data storage, calculates the maximal value of the data read out, and detects an angle that gives the maximal value as the skew angle. The image processing device, being thus configured, allows detecting and correcting the skew angle with high accuracy, even when the input image contains image elements such as photograph images and dot images.

Claims

1. An image processing device comprising:

a binary image generating part that generates binary image data from inputted image data; and

a skew angle detecting part that calculates a skew angle of the image data inputted by an input part from the binary image data generated by the binary image generating part,

wherein the skew angle detecting part includes;

a Hough transform part that executes Hough transform to the binary image data generated by the binary image generating part to generate Hough space data;

a frequency calculating part that executes a specific calculation to each of frequencies of data from the Hough space data generated by the Hough transform part, and adds an attained calculation result by each angle to generate first frequency calculation data; and

an angle detecting part that calculates an angle from the first frequency calculation data generated by the frequency calculating part.

2. The image processing device according to claim 1, wherein the skew angle detecting part includes plural skew angle detecting parts whose detecting conditions are different from each other.

3. The image processing device according to claim 2, wherein the detecting conditions of the plural skew angle detecting parts are varied step by step.

4. The image processing device according to claim 1, wherein:

the Hough transform part uses a surrounding frequency to smooth the frequency of the Hough space data generated, and

the frequency calculating part generates the first frequency calculation data from the frequencies of the Hough space data smoothed by the Hough transform part.

5. The image processing device according to claim 1, wherein:

the frequency calculating part uses a surrounding frequency calculation value to smooth a frequency calculation value of the first frequency calculation data generated, and

the angle detecting part calculates an angle from the frequency calculation value of the first frequency calculation data smoothed by the frequency calculating part.

6. The image processing device according to claim 1, wherein:

the skew angle detecting part includes a reduction part that executes reduction processing of the binary image data generated by the binary image generating part, and

the Hough transform part executes the Hough transform to the binary image data reduced by the reduction part to generate the Hough space data.

7. The image processing device according to claim 1, wherein the specific calculation is related to a function of a frequency containing a term of the n-th power (n>

1) of the frequency.

8. The image processing device according to claim 7, wherein n is 2.

9. The image processing device according to claim 1, wherein the angle detecting part detects a largest frequency calculation value from the first frequency calculation data generated by the frequency calculating part, and detects an angle that gives the largest frequency calculation value.

10. The image processing device according to claim 1, wherein the angle detecting part adds the first frequency calculation data generated by the frequency calculating part, with the phase shift of π

/2 (rad), to generate second frequency calculation data, detects a largest frequency calculation value from the second frequency calculation data, and detects an angle that gives the largest frequency calculation value.

11. The image processing device according to claim 1, wherein the angle detecting part detects a maximal value from the first frequency calculation data generated by the frequency calculating part, and detects an angle that gives the maximal value.

12. The image processing device according to claim 1, wherein the angle detecting part detects at least two maximum values or maximal values from the first frequency calculation data generated by the frequency calculating part, and detects an angle from a difference of the angles that give the maximum values or the maximal values.

13. The image processing device according to claim 12, wherein the difference of the angles is about π

/2 (rad).

14. The image processing device according to claim 1, wherein:

the binary image generating part includes a binarization part that executes binarization processing to the image data inputted by the input part, a pixel block extraction part that extracts a pixel block from binary image data generated by the binarization part, and a representative point extraction part that extracts a representative point of the pixel block extracted by the pixel block extraction part; and

the skew angle detecting part calculates a skew angle from the binary image data of the representative point of the pixel block extracted by the representative point extraction part.

15. The image processing device according to claim 14, wherein the Hough transform part executes the Hough transform to the representative point extracted by the representative point extraction part.

16. The image processing device according to claim 14, wherein:

the binary image generating part includes a reduction part that reduces the binary image data whose pixel block is extracted by the pixel block extraction part to extract a first pixel block, and

the representative point extraction part extracts outline pixels from the first pixel block extracted by the reduction part.

17. The image processing device according to claim 16, wherein:

the binary image generating part includes an expansion part that expands a region of the pixel block extracted by the pixel block extraction part to extract a second pixel block, and

the representative point extraction part extracts the outline pixels from the second pixel block extracted by the expansion part.

18. The image processing device according to claim 17, wherein:

the binary image generating part includes a contraction part that contracts the region of the second pixel block extracted by the expansion part to extract a third pixel block, and

the representative point extraction part extracts the outline pixels from the third pixel block extracted by the contraction part.

19. The image processing device according to claim 14, wherein the binarization part is a dynamic binarization part that executes a dynamic threshold binarization processing to the image data inputted by the input part.

20. The image processing device according to claim 14, wherein:

the binary image generating part includes a halftone dot region extraction part that extracts a dot region from the image data inputted by the input part, and

the representative point extraction part extracts the representative point of the pixel block from synthesized data of the image data pieces each outputted from the dynamic binarization part and the halftone dot region extraction part.

21. The image processing device according to claim 1, wherein:

the binary image generating part further includes an image region extraction part that extracts part of an image, and

the skew angle detecting part executes skew angle detection to the part of the image extracted by the image region extraction part.

22. The image processing device according to claim 1, wherein:

the binary image generating part further includes an image region partition part that partitions an image into plural regions, and

the skew angle detecting part executes angle detection to the regions each partitioned by the image region partition part, and detects a skew angle from the plural angles detected.

24. The image processing method according to claim 23, further comprising the steps of:

executing a binarization process to the inputted image data to generate the binary image data;

extracting a pixel block from the binary image data generated;

extracting a representative point of the extracted pixel block; and

calculating a skew angle from the binary image data of the representative point of the extracted pixel block.

23. An image processing method that generates binary image data from inputted image data, and detects a skew angle of the inputted image data from the binary image data generated, the method comprising the steps of:

executing Hough transform to the binary image data to generate Hough space data;

executing a specific calculation to each of frequencies of the Hough space data and adding an attained calculation result to each angle to generate first frequency calculation data; and

calculating an angle from the first frequency calculation data.

25. A recording medium readable by a computer, the recording medium storing a program of instructions executable by the computer to perform a function for image processing, the function comprising the steps of:

executing Hough transform to the binary image data to generate Hough space data;

executing a specific calculation to each of frequencies of the Hough space data and adding an attained calculation result to each angle to generate first frequency calculation data; and

calculating an angle from the first frequency calculation data.