Image processing apparatus, image processing system, image processing method, and computer-readable storage medium

• US 20020159633A1
• Filed: 03/08/2002
• Published: 10/31/2002
• Est. Priority Date: 03/13/2001
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Inoue, Hitoshi
• Granted Patent: US 6,993,183 B2
• Time in Patent Office: Days
• US Class Current: 382/170
• CPC Class Codes: G06T 2207/10116 X-ray image
• CPC Class Codes: G06T 2207/20012 Locally adaptive
• CPC Class Codes: G06T 2207/30004 Biomedical image processing
• CPC Class Codes: G06T 7/11 Region-based segmentation
• CPC Class Codes: G06T 7/136 involving thresholding

Abstract

An image processing apparatus creates a pixel value histogram of an objective image, and approximates a predetermined range of the created histogram by a bended line formed from two straight lines. Then the apparatus extracts a pixel value at a boundary between a predetermined region and another region of the objective image in accordance with the approximation.

Claims

1. An image processing apparatus comprising:

a histogram creation unit for creating a pixel value histogram of an objective image; and

an extraction unit for extracting a pixel value at a boundary between a predetermined region and another region of the objective image by approximating by a bended line formed from two straight lines a predetermined range of the histogram created by said histogram creation unit.

2. An apparatus according to claim 1, wherein the objective image includes a radiograph of an object, and the predetermined region includes a radiation through region or a region outside a radiation irradiation field.

3. An apparatus according to claim 1, wherein said extraction unit extracts a heel point of the bended line obtained by the approximation as the boundary pixel value.

4. An apparatus according to claim 1, wherein said extraction unit includes a setting unit for setting the predetermined range.

5. An apparatus according to claim 1, wherein said extraction unit includes a change unit for changing the predetermined range.

6. An apparatus according to claim 1, wherein said extraction unit extracts the boundary pixel value when the bended line obtained by the approximation satisfies a predetermined condition.

7. An apparatus according to claim 6, wherein the predetermined condition includes a condition that a ratio of errors of results of fitting using the bended line formed from the two straight lines is not more than a predetermined value and that change rates of slopes of the two straight lines are not less than a predetermined value.

8. An apparatus according to claim 6, wherein the predetermined condition concerns at least one of an approximate degree of the bended line and the slopes of the two straight lines.

9. An apparatus according to claim 8, wherein the predetermined condition concerning the approximate degree concerns variations in data of the histogram from the bended line.

10. An apparatus according to claim 8, wherein the predetermined condition concerning the slopes concerns changes in the slopes of the two straight lines.

11. An apparatus according to claim 1, further comprising:

a transform unit for transforming a pixel value in the predetermined region into a predetermined value.

12. An apparatus according to claim 11, wherein said transform unit transforms the pixel value in accordance with a continuous, differentiable transform function.

13. An apparatus according to claim 12, wherein the transform function substantially transforms a pixel value in the predetermined region into a predetermined value, substantially linearly transforms a pixel value in an other region, and nonlinearly transforms a pixel value near the boundary pixel value.

14. An apparatus according to claim 13, further comprising:

a smoothing unit for smoothing a value of a pixel nonlinearly transformed by the transform function in accordance with the value of the pixel and values of pixels around the pixel.

15. An apparatus according to claim 1, further comprising:

a display transform unit for performing pixel value transform depending on a display for the objective image before processing of said extraction unit.

16. An apparatus according to claim 11, further comprising:

an emphasis unit for performing predetermined emphasis processing for an image processed by said transform unit.

17. An apparatus according to claim 16, wherein the predetermined emphasis processing includes processing of changing a dynamic range of an image.

18. An apparatus according to claim 1, further comprising:

a recognition unit for recognizing the predetermined region on the basis of the boundary pixel value.

19. An image processing system constituted by a plurality of apparatuses communicatably connected to each other, wherein said system comprises said respective units of said image processing apparatus defined in any one of claims 1 to 18.

21. A computer-readable storage medium, wherein said storage medium stores a program for causing a computer to realize respective functions of said image processing apparatus defined in any one of claims 1 to 18.

22. A computer-readable storage medium, wherein said storage medium stores a program for causing a computer to realize respective functions of said image processing system defined in claim 19.

20. An image processing method comprising steps of:

creating a pixel value histogram of an objective image; and

extracting a pixel value at a boundary between a predetermined region and another region of the objective image by approximating by a bended line formed from two straight lines a predetermined range of the histogram created in the step of creating the histogram.

23. A computer-readable storage medium, wherein said storage medium stores a program for causing a computer to perform respective operations of the image processing method defined in claim 20.