Image processing apparatus and image processing method

• US 20040252343A1
• Filed: 11/22/2002
• Published: 12/16/2004
• Est. Priority Date: 11/22/2002
• Status: Active Grant

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation), Toshiba Tec Corporation (Toshiba Corporation)
• Original Assignee: Toshiba Tec Corporation (Toshiba Corporation)
• Inventors: Kawakami, Haruko
• Granted Patent: US 7,262,884 B2
• Time in Patent Office: Days
• US Class Current: 358/2.1
• CPC Class Codes: G06V 30/413 Classification of content, e.g. text, photographs or tables
• CPC Class Codes: H04N 1/40062 Discrimination between different image types, e.g. two-tone, continuous tone
• CPC Class Codes: H04N 1/56 Processing of colour picture signals H04N1/52 takes precedence

Abstract

A white background determination section performs a white background determination on the basis of a white threshold calculated by a white threshold calculation section and an area size selected by an area size determination section. A character discrimination section executes character recognition such that a condition for character discrimination is relaxed when the white background determination section determines that a pixel of interest belongs to a white background, and the condition for character discrimination is made stricter in other cases.

Claims

1. An image processing apparatus comprising:

a calculation section that calculates a value used to determine an attribute of an area on the basis of an image signal;

an area size determination section that determines an area size on the basis of a predetermined condition; and

an area attribute determination section that determines an attribute of a pixel of interest in the image signal, on the basis of the area size determined by the area size determination section and the value that is calculated by the calculation section and is used to determine the attribute of the area.

2. The image processing apparatus according to claim 1, wherein the calculation section calculates a white threshold, and the area size determination section determines the area size by counting a run-length of white pixels in a vicinity of the pixel of interest in the image signal, using the white threshold calculated by the calculation section.

3. The image processing apparatus according to claim 1, wherein the calculation section finds a maximum value Dmax and a minimum value Dmin within an original document and, using a preset white threshold ratio Rw, calculates a white threshold Dw=Dmin+(Dmax−

Dmin)×

Rw.

4. The image processing apparatus according to claim 1, wherein the calculation section finds a maximum value Dmax and a minimum value Dmin within an original document and, using a preset white threshold ratio Rw, calculates a white threshold Dw=Dmin+(Dmax−

Dmin)×

Rw, and

wherein when the value Dw is smaller than a predetermined threshold Dwth, the value Dwth is determined to be a white threshold, and when the value Dw is greater than the predetermined threshold Dwth, the value Dw is determined to be a white threshold.

5. The image processing apparatus according to claim 1, wherein the area size determination section counts a maximum run-length in a main scan direction and a maximum run-length in a sub-scan direction, determines the shorter of the maximum run-lengths to be a maximum run-length in the area, and selects the area size using this maximum run-length and a preset threshold.

6. The image processing apparatus according to claim 1, wherein the area attribute determination section finds, with use of a white threshold calculated by the calculation section, an occupation ratio of white pixels in an area of interest of the area size determined by the area size determination section, and

wherein when the found occupation ratio is greater than a predetermined first occupation ratio threshold, the area attribute determination section determines the pixel of interest to be a pixel in a white background area.

7. The image processing apparatus according to claim 6, wherein the area attribute determination section finds a difference value in a main scan direction and a difference value in a sub-scan direction in the area of interest of the area size determined by the area size determination section, finds a sum of each difference value, compares each sum with a preset threshold, and, when each sum is greater than the preset threshold, uses a second occupation ratio threshold that is greater than the first occupation ratio threshold.

8. The image processing apparatus according to claim 6, wherein the area attribute determination section finds a difference value in a main scan direction and a difference value in a sub-scan direction in the area of interest of the area size determined by the area size determination section, finds an average of each difference value, compares each average with a preset threshold, and, when each average is greater than the preset threshold, uses a second occupation ratio threshold that is greater than the first occupation ratio threshold.

9. The image processing apparatus according to claim 6, wherein the area attribute determination section finds a difference value in a main scan direction and a difference value in a sub-scan direction in the area of interest of the area size determined by the area size determination section, counts a number of locations where the difference value is greater than a preset first threshold, finds the count value both in the main scan direction and sub-scan direction, compares each count value with a preset second threshold, and, when each count value is greater than the second threshold, uses a second occupation ratio threshold that is greater than the first occupation ratio threshold.

10. The image processing apparatus according to claim 1, further comprising a character determination section that performs character determination under a first condition when the area attribute determination section determines that the pixel of interest belongs to a white background, and performs character determination under a second condition that is stricter than the first condition in other cases.

11. The image processing apparatus according to claim 1, wherein the area attribute determination section determines whether the pixel of interest is in a white background area with respect to areas of different sizes, using a white threshold calculated by the calculation section, and the image processing apparatus further includes a switching section that receives determination results from the area attribute determination section and outputs one of the determination results.

12. The image processing apparatus according to claim 11, wherein the switching section switches the determination result of each area size determined by the white background determination section to the determination result of the same area size as the area size determined by the area size determination section.

13. The image processing apparatus according to claim 1, further comprising an achromatic color determination section that determines, based on the image signal, whether an area of interest is composed of only an achromatic character, and a character discrimination section that performs character discrimination of the pixel of interest on the basis of a determination result of the area attribute determination section and a determination result of the achromatic color determination section.

14. The image processing apparatus according to claim 13, wherein the achromatic color determination section calculates color difference equivalent values C1cen and C2cen of a pixel with a maximum luminance Dmax of an original document, and determines that that the area of interest is composed of only an achromatic character when the following formula is satisfied:

((C1−

C1cen)/R1)²+((C2−

C2cen)/R2)²≦

1

where R1 and R2 designate a major axis and a minor axis of an oval representing an achromatic area.

15. An image processing method comprising:

calculating a value used to determine an attribute of an area on the basis of an image signal;

determining an area size on the basis of a predetermined condition; and

determining an attribute of a pixel of interest in the image signal, on the basis of the determined area size and the calculated value used to determine the attribute of the area.

16. An image processing method comprising:

calculating a white threshold to determine an attribute of an area on the basis of an image signal;

determining whether a pixel of interest in the image signal is located in a white background area with respect to areas of different sizes, using the calculated white threshold;

selecting one of a plurality of determination results with respect to the areas of different sizes, on the basis of a condition of a vicinity of the pixel of interest; and

altering an image area discrimination process, such as character discrimination for the pixel of interest, in accordance with the selected determination result.

17. An image processing method comprising:

determining, based on an image signal, whether an area of interest is composed of only an achromatic character;

calculating a value used to determine an attribute of an area on the basis of the image signal;

determining an area size on the basis of a predetermined condition;

determining an attribute of a pixel of interest in the image signal, on the basis of the determined area size and the calculated value used to determine the attribute of the area; and

performing character discrimination of the pixel of interest on the basis of a determination result of the attribute and a determination result as to whether the area of interest is composed of only an achromatic character.