Image processing apparatus

• US 6,763,129 B1
• Filed: 10/04/2000
• Issued: 07/13/2004
• Est. Priority Date: 10/05/1999
• Status: Expired due to Term

• Current Assignee: Toshiba Medical Systems Corporation (Canon Inc.)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Honda, Michitaka, Umazaki, Hiroko
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): Akhavannik, Hussein
• Application Number:
  US09/679,440
• Time in Patent Office: 1,378 Days
• Field of Search: 382/132, 382/205, 382/269
• US Class Current: 382/132
• CPC Class Codes: G06T 2207/10116 X-ray image
• CPC Class Codes: G06T 2207/20192 Edge enhancement; Edge preservation
• CPC Class Codes: G06T 2207/30101 Blood vessel; Artery; Vein; Vascular
• CPC Class Codes: G06T 5/20 using local operators
• CPC Class Codes: G06T 5/70 Denoising; Smoothing
• CPC Class Codes: G06T 7/194 involving foreground-background segmentation
• CPC Class Codes: G06T 7/73 using feature-based methods
• CPC Class Codes: G06V 10/30 Noise filtering

Abstract

An input image is inputted into a pre-process circuit and a spatial filter. The pre-process circuit emphasizes a linear shadow or an edge to some extent, or reduces noises overall. Following pre-processing, the image signal is supplied to a direction detection circuit, a direction and its intensity of an area of interest are detected. These two results of the detections are correlated with peripheral areas of interest to some extent by a vector filter. An output of the vector filter is supplied to a spatial filter coefficient generation circuit, and a filter coefficient of the spatial filter is decided. The spatial filter processes the input image based on the direction of the shadow and its intensity, whereby selectively suppressing noise components of the background in real time without damaging the contrasts of a linear shadow or an edge-like shadow.

Claims

1. An image processing apparatus comprising:

means for detecting a direction and an intensity of a linear or an edge-like shadow included in an image; and

means for processing the image using a spatial filter having a directivity according to the direction and the intensity detected by said detecting means, wherein said detecting means estimates dispersion of random noises within an area of interest based on an average value of pixel distribution within the area of interest, estimates probability distribution which is determined by the estimated dispersion of random noises and a matrix size of the area of interest with respect to an index representing intensity, and calculates a probability that intensity calculated based on pixel values within the area of interest can be taken under the estimated probability distribution, the calculated probability being the index representing intensity.

2. The image processing apparatus according to claim 1, wherein

a pixel value of the shadow is larger than a pixel value of a background of the image;

said detecting means detects a direction based on an orientation of eigen vector corresponding to a larger eigen value out of two eigen values of covariance matrix of an area of interest of the image; and

said processing means processes the image using a digital spatial filter whose frequency characteristic of the direction detected by said detecting means is different from a frequency characteristic of other directions.

3. The image processing apparatus according to claim 2, wherein

said detecting means sequentially detects a direction and an intensity of the shadow per an area of interest of the image while shifting the area of interest to a horizontal direction and a vertical direction;

and

said processing means processes the image using a spatial filter with a size of the area of interest while shifting the filter over the image and changing the directivity.

4. The image processing apparatus according to claim 2, wherein

said area of interest comprises at least 5×

5 pixel arrays; and

said detecting means performs a two-dimensional product-sum calculation between predetermined coefficients and pixel values in the area of interest and calculates a covariance matrix of the area of interest based on the result of the two-dimensional product-sum calculation.

5. The image processing apparatus according to claim 2, wherein said detecting means detects a ratio of two eigen values of a covariance matrix as an index of intensity of a direction.

6. The image processing apparatus according to claim 2, wherein said detecting means processes the image using a frequency reduction filter, and performs direction detection processing to a difference image between an output image from the frequency reduction filter and an input image to the frequency reduction filter.

7. The image processing apparatus according to claim 2, wherein

said detecting means performs direction detection processing after inverting a code of a pixel value of the image.

8. The image processing apparatus according to claim 2, wherein said detecting means performs direction detection processing after subtracting the image from the maximum value decided by the maximum bit number of the image.

9. The image processing apparatus according to claim 2, wherein said detecting means performs pre-processing for suppressing noise spectrum while emphasizing a band having signal spectrum of the image.

10. The image processing apparatus according to claim 1, wherein

a pixel value of the shadow is smaller than a pixel value of a background of the image;

said detecting means detects a direction based on an orientation of eigen vector corresponding to a smaller eigen value out of two eigen values of covariance matrix of an area of interest of the image; and

said processing means processes the image using a digital spatial filter whose frequency characteristic of the direction detected by said detecting means is different from a frequency characteristic of other directions.

11. The image processing apparatus according to claim 10, wherein

said detecting means sequentially detects a direction and an intensity of the shadow per an area of interest of the image while shifting the area of interest to a horizontal direction and a vertical direction;

and

said processing means processes the image using a spatial filter with a size of the area of interest while shifting the filter over the image and changing the directivity.

12. The image processing apparatus according to claim 10, wherein

said area of interest comprises at least 5×

5 pixel arrays; and

said detecting means performs a two-dimensional product-sum calculation between predetermined coefficients and pixel values in the area of interest and calculates a covariance matrix of the area of interest based on the result of the two-dimensional product-sum calculation.

13. The image processing apparatus according to claim 10, wherein said detecting means detects a ratio of two eigen values of a covariance matrix as an index of intensity of a direction.

14. The image processing apparatus according to claim 10, wherein said detecting means processes the image using a frequency reduction filter, and performs direction detection processing to a difference image between an output image from the frequency reduction filter and an input image to the frequency reduction filter.

15. The image processing apparatus according to claim 10, wherein said detecting means performs direction detection processing after inverting a code of a pixel value of the image.

16. The image processing apparatus according to claim 10, wherein said detecting means performs direction detection processing after subtracting the image from the maximum value decided by the maximum bit number of the image.

17. The image processing apparatus according to claim 10, wherein said detecting means performs pre-processing for suppressing noise spectrum while emphasizing a band having signal spectrum of the image.

18. The image processing apparatus according to claim 1, wherein

said detecting means sequentially detects a direction and an intensity of the shadow per an area of interest of the image while shifting the area of interest to a horizontal direction and a vertical direction;

and

said processing means processes the image using a spatial filter with a size of the area of interest while shifting the filter over the image and changing the directivity.

19. The image processing apparatus according to claim 1, wherein

said detecting means calculates a new covariance matrix by performing a weighted average to elements of an old covariance matrix of an area of interest set up and elements of a covariance matrix of a peripheral area of the area of interest and determines a pattern direction vector based on a direction and an eigen value of an eigen vector of the new of covariance matrix as indices of a pattern running direction and an intensity of the pattern direction of the area of interest;

and

said processing means processes the image using a spatial filter having a directivity according to the pattern direction vector determined by said detecting means.

20. The image processing apparatus according to claim 19, wherein said detecting means calculates new covariance matrixes of peripheral areas of the area of interest, calculates directions of eigen vectors of the peripheral areas, and determines a direction of eigen vector which is appeared in the largest number of areas as a pattern direction of the area of interest.

21. The image processing apparatus according to claim 1, wherein said detecting means processes the image using a frequency reduction filter, and performs direction detection processing to a difference image between an output image from the frequency reduction filter and an input image to the frequency reduction filter.

22. The image processing apparatus according to claim 1, wherein said detecting means performs direction detection processing after inverting a code of a pixel value of the image.

23. The image processing apparatus according to claim 1, wherein said detecting means performs direction detection processing after subtracting the image from the maximum value decided by the maximum bit number of the image.

24. The image processing apparatus according to claim 1, wherein said detecting means performs pre-processing for suppressing noise spectrum while emphasizing a band having signal spectrum of the image.

25. The image processing apparatus according to claim 1, wherein the index representing intensity is an eigen value obtained based on a covariance matrix around a position decided by a center position of an area of interest and a center of gravity of pixel distribution within the area of interest.

26. The image processing apparatus according to claim 1, wherein the index representing intensity is a difference or a ratio of eigen values obtained based on covariance matrixes around positions decided by a center position of an area of interest and a center of gravity of pixel distribution within the area of interest.

27. An image processing apparatus comprising:

means for detecting a direction and an intensity of a linear or an edge-like shadow included in an image; and

means for processing the image using a spatial filter having a directivity according to the direction and the intensity detected by said detecting means, wherein

said detecting means calculates a new covariance matrix by performing a weighted average to elements of an old covariance matrix of an area of interest set up and elements of a covariance matrix of a peripheral area of the area of interest and determines a pattern direction vector based on a direction and an eigen value of an eigen vector of the new of covariance matrix as indices of a pattern running direction and an intensity of the pattern direction of the area of interest; and

said processing means processes the image using a spatial filter having a directivity according to the pattern direction vector determined by said detecting means.

28. The image processing apparatus according to claim 27, wherein

a pixel value of the shadow is larger than a pixel value of a background of the image;

said detecting means detects a direction based on an orientation of eigen vector corresponding to a larger eigen value out of two eigen values of covariance matrix of an area of interest of the image; and

said processing means processes the image using a digital spatial filter whose frequency characteristic of the direction detected by said detecting means is different from a frequency characteristic of other directions.

29. The image processing apparatus according to claim 28, wherein said detecting means sequentially detects a direction and an intensity of the shadow per an area of interest of the image while shifting the area of interest to a horizontal direction and a vertical direction;

and

said processing means processes the image using a spatial filter with a size of the area of interest while shifting the filter over the image and changing the directivity.

30. The image processing apparatus according to claim 28, wherein

said area of interest comprises at least 5×

5 pixel arrays; and

said detecting means performs a two-dimensional product-sum calculation between predetermined coefficients and pixel values in the area of interest and calculates a covariance matrix of the area of interest based on the result of the two-dimensional product-sum calculation.

31. The image processing apparatus according to claim 28, wherein said detecting means detects a ratio of two eigen values of a covariance matrix as an index of intensity of a direction.

32. The image processing apparatus according to claim 28, wherein said detecting means processes the image using a frequency reduction filter, and performs direction detection processing to a difference image between an output image from the frequency reduction filter and an input image to the frequency reduction filter.

33. The image processing apparatus according to claim 28, wherein said detecting means performs direction detection processing after inverting a code of a pixel value of the image.

34. The image processing apparatus according to claim 28, wherein said detecting means performs direction detection processing after subtracting the image from the maximum value decided by the maximum bit number of the image.

35. The image processing apparatus according to claim 28, wherein said detecting means performs pre-processing for suppressing noise spectrum while emphasizing a band having signal spectrum of the image.

36. The image processing apparatus according to claim 27, wherein

a pixel value of the shadow is smaller than a pixel value of a background of the image;

said detecting means detects a direction based on an orientation of eigen vector corresponding to a smaller eigen value out of two eigen values of covariance matrix of an area of interest of the image; and

said processing means processes the image using a digital spatial filter whose frequency characteristic of the direction detected by said detecting means is different from a frequency characteristic of other directions.

37. The image processing apparatus according to claim 36, wherein

said detecting means sequentially detects a direction and an intensity of the shadow per an area of interest of the image while shifting the area of interest to a horizontal direction and a vertical direction;

and

said processing means processes the image using a spatial filter with a size of the area of interest while shifting the filter over the image and changing the directivity.

38. The image processing apparatus according to claim 36, wherein

said area of interest comprises at least 5×

5 pixel arrays; and

said detecting means performs a two-dimensional product-sum calculation between predetermined coefficients and pixel values in the area of interest and calculates a covariance matrix of the area of interest based on the result of the two-dimensional product-sum calculation.

39. The image processing apparatus according to claim 36, wherein said detecting means detects a ratio of two eigen values of a covariance matrix as an index of intensity of a direction.

40. The image processing apparatus according to claim 36, wherein said detecting means processes the image using a frequency reduction filter, and performs direction detection processing to a difference image between an output image from the frequency reduction filter and an input image to the frequency reduction filter.

41. The image processing apparatus according to claim 36, wherein said detecting means performs direction detection processing after inverting a code of a pixel value of the image.

42. The image processing apparatus according to claim 36, wherein said detecting means performs direction detection processing after subtracting the image from the maximum value decided by the maximum bit number of the image.

43. The image processing apparatus according to claim 36, wherein said detecting means performs pre-processing for suppressing noise spectrum while emphasizing a band having signal spectrum of the image.

44. The image processing apparatus according to claim 27, wherein

said detecting means sequentially detects a direction and an intensity of the shadow per an area of interest of the image while shifting the area of interest to a horizontal direction and a vertical direction;

and

said processing means processes the image using a spatial filter with a size of the area of interest while shifting the filter over the image and changing the directivity.

45. The image processing apparatus according to claim 27, wherein said detecting means calculates new covariance matrixes of peripheral areas of the area of interest, calculates directions of eigen vectors of the peripheral areas, and determines a direction of eigen vector which is appeared in the largest number of areas as a pattern direction of the area of interest.

46. The image processing apparatus according to claim 27, wherein said detecting means processes the image using a frequency reduction filter, and performs direction detection processing to a difference image between an output image from the frequency reduction filter and an input image to the frequency reduction filter.

47. The image processing apparatus according to claim 27, wherein said detecting means performs direction detection processing after inverting a code of a pixel value of the image.

48. The image processing apparatus according to claim 27, wherein said detecting means performs direction detection processing after subtracting the image from the maximum value decided by the maximum bit number of the image.

49. The image processing apparatus according to claim 27, wherein said detecting means performs pre-processing for suppressing noise spectrum while emphasizing a band having signal spectrum of the image.

50. The image processing apparatus according to claim 27, wherein said detecting means estimates dispersion of random noises within an area of interest based on an average value of pixel distribution within the area of interest, estimates probability distribution which is determined by the estimated dispersion of random noises and a matrix size of the area of interest with respect to an index representing intensity, and calculates a probability that intensity calculated based on pixel values within the area of interest can be taken under the estimated probability distribution, the calculated probability being the index representing intensity, and the index representing intensity is an eigen value obtained based on a covariance matrix around a position decided by a center position of an area of interest and a center of gravity of pixel distribution within the area of interest.

51. The image processing apparatus according to claim 27, wherein said detecting means estimates dispersion of random noises within an area of interest based on an average value of pixel distribution within the area of interest, estimates probability distribution which is determined by the estimated dispersion of random noises and a matrix size of the area of interest with respect to an index representing intensity, and calculates a probability that intensity calculated based on pixel values within the area of interest can be taken under the estimated probability distribution, the calculated probability being the index representing intensity, and the index representing intensity is a difference or a ration of eigen values obtained based on covariance matrixes around positions decided by a center position of an area of interest and a center of gravity of pixel distribution within the area of interest.