Method and system for correcting direction or orientation of document image

• US 20030174904A1
• Filed: 01/15/2003
• Published: 09/18/2003
• Est. Priority Date: 01/16/2002
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Yamaai, Toshifumi
• Granted Patent: US 7,151,859 B2
• Time in Patent Office: Days
• US Class Current: 382/292
• CPC Class Codes: G06V 30/10 Character recognition
• CPC Class Codes: G06V 30/1478 of characters or characters lines

Abstract

A document image is often accidentally placed at an undesirable angle during image scanning. In order to correct the orientation of the image document, an angle must be determined based upon the document image. In determining the angle, the document image is processed to reverse the brightness as necessary.

Claims

1. A method of detecting the direction of a document image, comprising the steps of:

inputting the document image in original multi-value data;

digitizing the multi-value data into digitized image data;

detecting the direction of the document image based upon the digitized image data;

in case the direction detection failed, reversing brightness of the original multi-value data into brightness reversed image data;

digitizing the brightness reversed image data into digitized brightness reversed image data; and

detecting the direction of the document image based upon the digitized brightness reversed image data.

2. The method of detecting the direction of a document image according to claim 1 further comprising an additional step of generating the multi-value data in gray-scale prior to the initial digitizing step.

3. The method of detecting the direction of a document image according to claim 1 further comprising an additional step of correcting the direction of the document image based upon the detected direction.

4. A method of detecting the direction of a document image, comprising the steps of:

inputting the document image in original multi-value data;

determining whether the document image has been reversed in brightness; and

in case that the document image has not been reversed in brightness, digitizing the multi-value data into digitized image data; and

detecting the direction of the document image based upon the digitized image data;

or

in case that the document image has been reversed in brightness, reversing brightness of the original multi-value data into brightness reversed image data;

digitizing the brightness reversed image data into digitized brightness reversed image data; and

detecting the direction of the document image based upon the digitized brightness reversed image data.

5. The method of detecting the direction of a document image according to claim 4 further comprising an additional step of generating the multi-value data in gray-scale prior to said determining step.

6. The method of detecting the direction of a document image according to claim 4 further comprising an additional step of correcting the direction of the document image based upon the detected direction.

7. The method of detecting the direction of a document image according to claim 4 wherein said reversing step modifies a color map of the original multi-value data.

8. The method of detecting the direction of a document image according to claim 4 wherein said determining step further comprises the following steps of:

digitizing the multi-value data into digitized image data;

extracting a first set of minimal circumscribing rectangles containing continuous black pixels from the digitized image data;

counting a first number of black pixels in the first set of the extracted minimal circumscribing rectangles;

reversing brightness of the original multi-value data into brightness reversed image data;

digitizing the brightness reversed image data into digitized brightness reversed image data;

extracting a second set of minimal circumscribing rectangles containing continuous black pixels from the digitized brightness reversed image data;

counting a second number of black pixels in the second set of the extracted minimal circumscribing rectangles; and

determining the brightness reversal based upon the first number and the second number.

9. The method of detecting the direction of a document image according to claim 8 further comprising an additional steps of:

excluding any one of the first set of the extracted minimal circumscribing rectangles that touches edges to have first remaining minimal circumscribing rectangles before counting the first number; and

excluding any one of the second set of the extracted minimal circumscribing rectangles that touches edges to have second remaining minimal circumscribing rectangles before counting the second number.

10. The method of detecting the direction of a document image according to claim 9 further comprising an additional steps of:

excluding any one of the black pixels that is continuous with the edges in the first remaining minimal circumscribing rectangles before counting the first number; and

excluding any one of the black pixels that is continuous with the edges in the second remaining minimal circumscribing rectangles before counting the second number.

11. The method of detecting the direction of a document image according to claim 4 wherein said determining step further comprises the following steps of:

digitizing the multi-value data into digitized image data;

dividing the digitized image data into first divided areas according to a first predetermined rule;

evaluating the first divided areas to obtain the first division evaluation;

reversing brightness of the original multi-value data into brightness reversed image data;

digitizing the brightness reversed image data into digitized brightness reversed image data;

dividing the digitized brightness reversed image data into second divided areas according to a second predetermined rule;

evaluating the second divided areas to obtain the second division evaluation; and

determining the brightness reversal based upon the first division evaluation and the second division evaluation.

12. The method of detecting the direction of a document image according to claim 4 wherein said determining step further comprises the following steps of:

digitizing the multi-value data into digitized image data;

extracting minimal circumscribing rectangles containing only white pixels from the digitized image data;

sorting the extracted minimal circumscribing rectangles according to area;

adding the area of a predetermined number of the largest ones of the extracted minimal circumscribing rectangles to generate a total white pixel minimal circumscribing rectangle area;

obtaining a ratio of the total white pixel minimal circumscribing rectangle area to a total area of the digitized image data; and

determining the brightness reversal based upon the ratio with respect to a first predetermined threshold value.

13. The method of detecting the direction of a document image according to claim 4 wherein said determining step further comprises the following steps of:

digitizing the multi-value data into digitized image data;

extracting minimal circumscribing rectangles containing only white pixels from the digitized image data;

sorting the extracted minimal circumscribing rectangles according to area;

adding the area of a predetermined number of the largest ones of the extracted minimal circumscribing rectangles to generate a total white pixel minimal circumscribing rectangle area;

determining a largest minimal circumscribing rectangular area containing all of the extracted minimal circumscribing rectangles;

obtaining a ratio of the total white pixel minimal circumscribing rectangle area to the largest minimal circumscribing rectangular area; and

determining the brightness reversal based upon the ratio with respect to a first predetermined threshold value.

14. The method of detecting the direction of a document image according to claim 4 wherein said determining step further comprises the following steps of:

reducing the multi-value data by a predetermined percentage;

digitizing the multi-value data into digitized image data;

extracting minimal circumscribing rectangles containing only white pixels from the digitized image data;

sorting the extracted minimal circumscribing rectangles according to area;

comparing an area of the white pixels in each of the predetermined number of the largest ones of the extracted minimal circumscribing rectangles to a second predetermined threshold value to generate a comparison result;

adding the area of the largest ones of the extracted minimal circumscribing rectangles to generate a total white pixel minimal circumscribing rectangle area based upon the comparison result;

determining a largest minimal circumscribing rectangular area containing all of the extracted minimal circumscribing rectangles;

obtaining a ratio of the total white pixel minimal circumscribing rectangle area to the largest minimal circumscribing rectangular area; and

determining the brightness reversal based upon the ratio with respect to a third predetermined threshold value.

15. A system for detecting the direction of a document image, comprising:

a document input unit for generating the document image in original multi-value data;

a brightness reversing unit for reversing brightness of the document image;

a digitizing unit connected to said document input unit for digitizing the multi-value data into digitized image data;

a direction detection unit connected to said brightness reversing unit and said digitizing unit for detecting the direction of the document image based upon the digitized image data, in case said direction detection unit failing to detect the direction, said brightness reversing unit reversing brightness of the original multi-value data into brightness reversed image data, said digitizing unit digitizing the brightness reversed image data into digitized brightness reversed image data so that said direction detection unit detecting the direction of the document image based upon the digitized brightness reversed image data.

16. The system for detecting the direction of a document image according to claim 15 further comprising a document direction correction unit connected to said direction detection unit for correcting the direction of the document image based upon the detected direction.

17. A system for detecting the direction of a document image, comprising:

a document input unit for generating the document image in original multi-value data;

a digitizing unit connected to said document input unit for digitizing the document image;

a brightness reversing unit connected to said document input unit for reversing brightness of the document image;

a direction detection unit connected to said document input unit for detecting direction of the document image; and

a brightness reversal determination unit connected to said document input unit for determining whether the document image has been reversed in brightness, in case that the document image has not been reversed in brightness, said digitizing unit digitizing the multi-value data into digitized image data, said direction detection unit detecting the direction of the document image based upon the digitized image data, or in case that the document image has been reversed in brightness, said brightness reversing unit reversing brightness of the original multi-value data into brightness reversed image data, said digitizing unit digitizing the brightness reversed image data into digitized brightness reversed image data, and said direction detection unit detecting the direction of the document image based upon the digitized brightness reversed image data.

18. The system for detecting the direction of a document image according to claim 17 further comprising a document direction correction unit connected to said direction detection unit for correcting the direction of the document image based upon the detected direction.

19. The system for detecting the direction of a document image according to claim 17 wherein said brightness reversing unit reversing the brightness by modifying a color map of the original multi-value data.

20. The system for detecting the direction of a document image according to claim 17 wherein said brightness reversal determination unit determines the brightness reversal based upon a first number and a second number, said digitizing unit digitizing the multi-value data into digitized image data, said brightness reversal determination unit extracting a first set of minimal circumscribing rectangles containing continuous black pixels from the digitized image data, said brightness reversal determination unit counting the first number of black pixels in the first set of the extracted minimal circumscribing rectangles, said brightness reversing unit reversing brightness of the original multi-value data into brightness reversed image data, said digitizing unit digitizing the brightness reversed image data into digitized brightness reversed image data, said brightness reversal determination unit extracting a second set of minimal circumscribing rectangles containing continuous black pixels from the digitized brightness reversed image data, and said brightness reversal determination unit counting the second number of black pixels in the second set of the extracted minimal circumscribing rectangles.

21. The system for detecting the direction of a document image according to claim 20 wherein said brightness reversal determination unit excludes any one of the first set of the extracted minimal circumscribing rectangles that touches edges to have first remaining minimal circumscribing rectangles before counting the first number, said brightness reversal determination unit also excluding any one of the second set of the extracted minimal circumscribing rectangles that touches edges to have second remaining minimal circumscribing rectangles before counting the second number.

22. The system for detecting the direction of a document image according to claim 21 wherein said brightness reversal determination unit further excludes any one of the black pixels that is continuous with the edges in the first remaining minimal circumscribing rectangles before counting the first number, said brightness reversal determination unit further excluding any one of the black pixels that is continuous with the edges in the second remaining minimal circumscribing rectangles before counting the second number.

23. The system for detecting the direction of a document image according to claim 17 wherein said brightness reversal determination unit determines the brightness reversal based upon a first division evaluation result and a second division evaluation result, said digitizing unit digitizing the multi-value data into digitized image data, said brightness reversing unit reversing brightness of the original multi-value data into brightness reversed image data, said digitizing unit digitizing the brightness reversed image data into digitized brightness reversed image data;

claim 17 further comprising;

a first area division unit connected to said digitizing unit for dividing the digitized image data into first divided areas according to a first predetermined rule;

a second area division unit connected to said digitizing unit for dividing the digitized brightness reversed image data into second divided areas according to a second predetermined rule; and

an area evaluation unit connected to said first and second area division units for evaluating the first divided areas to obtain the first division evaluation result and evaluating the second divided areas to obtain the second division evaluation result.

24. The system for detecting the direction of a document image according to claim 17 wherein said brightness reversal determination unit determines the brightness reversal based upon a ratio with respect to a first predetermined threshold value, said digitizing unit digitizing the multi-value data into digitized image data, said brightness reversal determination unit extracting minimal circumscribing rectangles containing only white pixels from the digitized image data, said brightness reversal determination unit sorting the extracted minimal circumscribing rectangles according to area, said brightness reversal determination unit adding the area of a predetermined number of the largest ones of the extracted minimal circumscribing rectangles to generate a total white pixel minimal circumscribing rectangle area, and said brightness reversal determination unit obtaining the ratio of the total white pixel minimal circumscribing rectangle area to a total area of the digitized image data.

25. The system for detecting the direction of a document image according to claim 17 wherein said brightness reversal determination unit determines the brightness reversal based upon a ratio with respect to a first predetermined threshold value, said digitizing unit digitizing the multi-value data into digitized image data, said brightness reversal determination unit extracting minimal circumscribing rectangles containing only white pixels from the digitized image data, said brightness reversal determination unit sorting the extracted minimal circumscribing rectangles according to area, said brightness reversal determination unit adding the area of a predetermined number of the largest ones of the extracted minimal circumscribing rectangles to generate a total white pixel minimal circumscribing rectangle area, said brightness reversal determination unit determining a largest minimal circumscribing rectangular area containing all of the extracted minimal circumscribing rectangles, and said brightness reversal determination unit obtaining the ratio of the total white pixel minimal circumscribing rectangle area to the largest minimal circumscribing rectangular area.

26. The system for detecting the direction of a document image according to claim 17 wherein said brightness reversal determination unit determines the brightness reversal based upon the ratio with respect to a third predetermined threshold value, said brightness reversal determination unit reducing the multi-value data by a predetermined percentage, said digitizing unit digitizing the multi-value data into digitized image data, said brightness reversal determination unit extracting minimal circumscribing rectangles containing only white pixels from the digitized image data, said brightness reversal determination unit sorting the extracted minimal circumscribing rectangles according to area, said brightness reversal determination unit comparing an area of the white pixels in each of the predetermined number of the largest ones of the extracted minimal circumscribing rectangles to a second predetermined threshold value to generate a comparison result, said brightness reversal determination unit adding the area of the largest ones of the extracted minimal circumscribing rectangles to generate a total white pixel minimal circumscribing rectangle area based upon the comparison result, said brightness reversal determination unit determining a largest minimal circumscribing rectangular area containing all of the extracted minimal circumscribing rectangles, and said brightness reversal determination unit obtaining the ratio of the total white pixel minimal circumscribing rectangle area to the largest minimal circumscribing rectangular area.