Image processing apparatus and method

• US 5,748,778 A
• Filed: 09/05/1995
• Issued: 05/05/1998
• Est. Priority Date: 09/08/1994
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Onoguchi, Kazunori
• Primary Examiner(s): Couso, Yon
• Assistant Examiner(s): NGUYEN, HA T
• Application Number:
  US08/523,428
• Time in Patent Office: 973 Days
• Field of Search: 382/199, 382/170, 382/171, 382/174, 382/193, 382/194, 382/131, 382/132, 358/522
• US Class Current: 382/199
• CPC Class Codes: G06V 10/28 Quantising the image, e.g. histogram thresholding for discrimination between background and foreground patterns

Abstract

An image processing apparatus of the present invention extracts a boundary point between a white pixel area and a black pixel area on a binary image. In the image processing apparatus, a scan line set section sets a scan line on the binary image. A cumulative histogram creation section examines each pixel on the scan line and creates a cumulative histogram, a predetemined value being added whenever one of a black pixel and a white pixel is extracted, corresponding to pixel position of the scan line. A boundary point extraction section extracts a point from the binary image corresponding to a point on the histogram where the display moves from a relatively flat part to a monotone increasing part and determines the pixel position corresponding to the extracted point on the scan line as a boundary point which indicates a transition from one pixel area to the other pixel area.

Claims

1. Image processing apparatus, comprising:

scan line set means for arbitrarily setting a scan line on a binary image;

cumulative histogram creation means for examining each pixel on the scan line of the binary image and for creating a cumulative histogram display having a first axis representing a pixel position in the scan line and a second axis perpendicular to the first axis representing a cumulative value;

means for adding a predetermined value to the cumulative value on the second axis whenever a black pixel is detected on the scan line, wherein a position of the cumulative value corresponds to the pixel position on the scan line of the first axis; and

boundary point extraction means for extracting a pixel position on the scan line of the first axis corresponding to a point on a curve of the histogram, the histogram moving from a relatively flat part to a monotone increasing part at a predetermined angle with respect to a direction of the flat part and for detecting a point corresponding to the extracted pixel position from the binary image when a length of the relatively flat part is above a first threshold value and a length of the monotone increasing part is above a second threshold value, wherein the detected point is a boundary point which indicates a transition from the white pixel area to the black pixel area of the binary image.

2. Image processing apparatus according to claim 1,

wherein said cumulative histogram creation means includes means for creating a cumulative histogram having a horizontal axis which represents each pixel position of the scan line and a vertical axis which represents a cumulative value, one being added to the cumulative value whenever a black pixel is extracted;

and wherein said extracted point corresponds to a point on the histogram where the display moves from the relatively flat part to the monotone increasing part at an angle of about 45°

with respect to the direction of the flat part.

3. Image processing apparatus according to claim 1,

wherein said cumulative histogram creation means examines pixels on the scan line of the binary image at intervals of a predetermined number, and creates the cumulative histogram having a horizontal axis which represents each pixel position of the scan line and a vertical axis which represents a cumulative value, the predetermined number being added to the cumulative value whenever black pixel is extracted;

and wherein said extracted point corresponds to a point on the histogram where the display moves from the relatively flat part to the monotone increasing part at an angle of about 45°

with respect to the direction of the flat part.

4. Image processing apparatus according to claim 1,

wherein said cumulative histogram creation means creates the cumulative histogram, a predetermined value being added to the cumulative histogram whenever a black pixel is extracted at the same pixel position of plural lines including the scan line as a center line.

5. Image processing apparatus according to claim 1,

wherein said scan line set means sets plural scan lines, the plural scan lines being utilized to extract a boundary line by linking each boundary point extracted from the plural scan lines, between a white pixel area and a black pixel area on the binary image.

6. Image processing apparatus, comprising:

scan line set means for arbitrarily setting a scan line of a binary image;

cumulative histogram creation means for examining each pixel on the scan line of the binary image and for creating a cumulative histogram display having a first axis representing a pixel position in the scan line and a second axis perpendicular to the first axis representing a cumulative value;

means for adding a predetermined value to the cumulative value on the second axis whenever a white pixel is detected on the scan line, wherein a position of the cumulative value corresponds to the pixel position on the scan line of the first axis; and

boundary point extraction means for extracting a pixel position on the scan line of the first axis corresponding to a point on a curve of the histogram, the histogram moving from a relatively flat part to a monotone increasing part at a predetermined angle with respect to a direction of the flat part and for detecting a point corresponding to the extracted pixel position from the binary image when a length of the relatively flat part is above a first threshold value and a length of the monotone increasing part is above a second threshold value, wherein the detected point is a boundary point which indicates a transition from the black pixel area to the white pixel area of the binary image.

7. Image processing apparatus according to claim 6,

wherein said cumulative histogram creation means includes means for creating a cumulative histogram having a horizontal axis which represents each pixel position of the scan line and a vertical axis which represents a cumulative value, one being added to the cumulative value whenever a white pixel is extracted;

and wherein said extracted point corresponds to a point on the histogram where the display moves from the flat part to the monotone increasing part at an angle of about 45°

with respect to the direction of the flat part.

8. Image processing apparatus according to claim 6,

wherein said cumulative histogram creation means examines pixels on the scan line of the binary image at intervals of a predetermined number, and creates a cumulative histogram having a horizontal axis which represents each pixel position on the scan line and a vertical axis which represents a cumulative value, the predetermined number being added to the cumulative value whenever a white pixel is extracted,

and wherein said boundary point corresponds to a point on the histogram where the display moves from the relatively flat part to the monotone increasing part at an angle of about 45°

with respect to the direction of the flat part.

9. Image processing apparatus according to claim 6,

wherein said cumulative histogram creation means creates the cumulative histogram, a predetermined value being added to the cumulative histogram whenever a white pixel is extracted at the same pixel position of plural lines including the scan line as a center line.

10. Image processing apparatus according to claim 6,

wherein said scan line set means sets plural scan lines, the plural scan lines being utilized to extract a boundary line by linking each boundary point extracted from the plural scan lines, between a white pixel area and a black pixel area on the binary image.

11. Image processing method comprising the steps of:

setting a scan line on a binary image arbitrarily;

examining each pixel on the scan line of the binary image;

creating a cumulative histogram having a first axis representing a pixel position in the scan line and a second axis perpendicular to the first axis representing a cumulative value;

adding a predetermined value to the cumulative value on the second axis whenever a black pixel is detected on the scan line, where a position of the cumulative value corresponds to the pixel position on the scan line of the first axis;

extracting a pixel position on the scan line corresponding to a point on the curve of the histogram, the histogram moving from a relatively flat part to a monotone increasing part at a predetermined angle with respect to a direction of the flat part; and

detecting a point corresponding to the extracted pixel position from the binary image when a length of the relatively flat part is above a first threshold value and a length of the monotone increasing part is above a second threshold value, wherein the detected point is a boundary point which indicates a transition from the white pixel area to the black pixel area of the binary image.

12. Image processing method comprising the steps of:

setting a scan line on a binary image arbitrarily;

examining each pixel on the scan line of the binary image;

creating a cumulative histogram having a first axis representing a pixel position in the scan line and a second axis perpendicular to the first axis representing a cumulative value;

adding a predetermined value to the cumulative value on the second axis whenever a white pixel is detected on the scan line, where a position of the cumulative value corresponds to the pixel position on the scan line of the first axis;

extracting a pixel position on the scan line corresponding to a point on the curve of the histogram, the histogram moving from a relatively flat part to a monotone increasing part at a predetermined angle with respect to a direction of the flat part; and

detecting a point corresponding to the extracted pixel position from the binary image when a length of the relatively flat part is above a first threshold value and a length of the monotone increasing part is above a second threshold value, wherein the detected point is a boundary point which indicates a transition from the black pixel area to the white pixel area of the binary image.