Method and apparatus for determining image similarity and position

• US 6,154,566 A
• Filed: 05/15/1997
• Issued: 11/28/2000
• Est. Priority Date: 05/15/1996
• Status: Expired due to Term

• Current Assignee: Omron Corporation
• Original Assignee: Omron Corporation
• Inventors: Hisamori, Yoshihiko, Mine, Naomichi
• Primary Examiner(s): Mehta, Bhavesh
• Assistant Examiner(s): PATEL, KANJIBHAI B
• Application Number:
  US08/856,598
• Time in Patent Office: 1,293 Days
• Field of Search: 382/219, 382/220, 382/242, 382/151, 382/199, 382/218, 382/287, 382/197, 382/201, 382/206, 382/209, 382/266
• US Class Current: 382/219
• CPC Class Codes: G06V 10/751 Comparing pixel values or logical combinations thereof, or feature values having positional relevance, e.g. template matching

Abstract

An apparatus for determining a similarity between model image and inputted image, which is robust even if the background of said inputted image is partly changed. The similarity is calculated from an edge direction of an inputted image, an edge direction of a model image and a weight related to the model image. The calculating steps used are (1) calculating an edge direction difference between an inputted model image and a model image, (2) calculating weights related to model image, (3) multiplying edge directions and weights, (4) calculating a sum of the multiplication, (5) calculating a sum of the weights, and (6) calculating a similarity by dividing the sum of the multiplication by the sum of the weights.

Claims

1. An image processing apparatus for determining a similarity between first image data and second image data conprising:

an edge direction unit for determining an edge direction at each pixel of said first image data and an edge direction at each pixel of said second image data;

an edge magnitude unit for determining an edge magnitude at each pixel of one of said images; and

a similarity unit for determining a similarity between said first and second images by reducing a background contrast by using the edge directions and magnitudes for each pixel of said one image and edge directions for each pixel of the other of said images.

2. An image processing apparatus as in claim 1, wherein said one image is a model image and said other image is an image which is input to said processing apparatus for similarity comparison with said model image.

3. An image processing apparatus as in claim 1, wherein said similarity unit comprises a difference calculating unit for determining the difference between edge directions of said first and second images.

4. An image processing apparatus as in claim 3, wherein said similarity unit further comprises:

an evaluation unit for evaluating the differences between the edge directions of said first and second images determined by said difference calculating unit.

5. An image processing apparatus as in claim 4, wherein said similarity unit further comprises:

a summing unit for summing evaluating values obtained from said evaluation unit in accordance with the edge magnitudes of said other image to produce a degree of similarity.

6. An image processing apparatus as in claim 5, wherein said similarity unit further comprises:

a division unit for dividing the degree of similarity produced by said summing unit by a summing of the edge magnitude values of said other image.

7. An image processing apparatus as in claims 5 or 6, wherein said weighting is in accordance with a sum of the edge magnitudes of said other image.

8. An image processing apparatus according to claims 5 or 6, wherein said evaluation unit calculates a cosine of a value produced by subtracting edge directions of each pixel of said first and second images.

9. An image processing apparatus as in claims 5 or 6, wherein said difference calculating unit subtracts the edge directions of said first and second images, and wherein said evaluation unit operates such that if said subtraction is between first predetermined values which includes 0, said evaluating-value is 1, and if said subtraction is between second predetermined values, said evaluating-value is -1, and if said subtraction is between third predetermined values, said evaluating-value is 0.

10. An image processing apparatus in accordance with claims 5 or 6, wherein said summing unit sums those weighted evaluating-values which are greater than a predetermined value.

11. An image processing apparatus in accordance with claims 5 or 6, wherein said edge direction unit calculates edge directions at a predetermined region of said first image data, and said evaluating difference of edge direction unit calculates evaluating-values by subtracting said edge directions from edge directions at predetermined regions of said second image data.

12. An image processing method for determining a similarity between first image data and second image data comprising the steps of:

(a) calculating edge directions at each pixel of said first image data and calculating edge directions at each pixel of said second image data;

(b) calculating evaluating-values by talkng the difference between the edge direction of each pixel of said first image data from an edge direction of each pixel of said second image data and reducing a background contrast;

(c) associating weight-values to said evaluating-values, said weight-values being calculated from one of said image data; and

(d) summing the weight associated evaluating-values at each pixel and providing an indication of a degree of similarity between said first and second image data based on the result of the summing.

13. An image processing method according to claim 12, wherein said weight-value is a sum of an edge magnitude at each pixel of said one image data.

14. An image processing method according to claim 12, wherein said calculating evaluating-values step takes a cosine function of values produced by subtracting said the edge direction of corresponding pixels of said first and second image data.

15. An image processing method according to claim 12, wherein if said subtraction is between first predetermined values which includes 0, said evaluating-value is 1, and if said subtraction is between second predetermined values, said evaluating-value is -1, and if said subtraction is between third predetermined values, said evaluating-value is 0.

16. A position detecting apparatus for detecting an image position comprising:

an edge direction unit for determining an edge direction at each pixel of said first image data and an edge direction at each pixel of said second image data;

an edge magnitude unit for determining an edge magnitude t each pixel of one of said images;

a similarity unit for determining a similarity between said first and second images by reducing a background contrast by using the edge directions and magnitudes for each pixel of said one image and edge directions for each pixel of the other of said images;

a scanner for causing a similarity between said first and second images to be determined at a plurality of scanning locations where said first and second images are shifted relative to each other; and

a position detector for detecting a position of said first image data relative to said second image data which produces the highest similarity.

17. An image processing apparatus for determining a similarity between first image data and second image data comprising:

an image memory unit for storing a plurality of second image data;

an edge direction unit for determining an edge direction at each pixel of said first image data and an edge direction at each pixel of said second image data;

an edge magnitude unit for determining an edge magnitude at each pixel of one of said images;

a similarity unit for determining a similarity between said first and second images by reducing a background contrast by using the edge directions and magnitudes for each pixel of said one image and edge direction for each pixel of the other of said images;

said similarity being determined between said first image data and each of said second image data, said memory unit storing the similarities determined between said image data and each of said second image data; and

a maximum similarity memory for storing the maximum similarity among the similarities determined with respect to all of said second images.

18. An image processing apparatus for determining a similarity between a first image data and a second image data comprising:

an edge direction unit for determining an edge direction at each pixel of said first image data and an edge direction at each pixel of a plurality of said second image data;

an edge direction memory for storing edge directions of pixels of a plurality of said second image data;

a representative edge direction unit for calculating a representative edge direction from said stored edge directions of pixels of said plurality of said second image data;

an evaluating difference of edge direction unit for calculating evaluating-values obtained by subtracting edge directions of the pixels of said first image data form pixels of representative edge directions of corresponding pixels and reducing a background contrast;

a weighting unit for weighting a value calculated film said second image data to said evaluating-values; and

a summing unit for summing weighted evaluating-values at each pixel of said second image data.

19. An image processing apparatus according to claim 18, wherein said representative edge direction unit calculates a mean of the edge directions of the pixels of a plurality of said second image data.

20. An image processing apparatus according to claim 18, wherein said weighting value is an edge magnitude of at each pixel of said second image data.

21. An image processing apparatus according to claim 18, wherein said weighting value is an representative edge magnitude at each pixel, and said representative edge magnitude is calculated from edge magnitudes of the pixels of said plurality of said second image data.

22. An image processing apparatus according to claim 18, wherein said weighting value is an representative edge magnitude at each pixel, and said representative edge magnitude is a mean of edge directions of the pixels of said plurality of said second image data.

23. A position detecting apparatus for detecting an image position comprising:

an edge direction unit for determining edge directions at each pixel of a first image data and edge directions of each pixel of a second image data;

an edge direction memory for storing edge directions of pixels of a plurality of said second image data;

a representative edge direction unit for calculating a representative edge direction from said stored edge directions of pixel of said plurality of said second image data;

an evaluating difference of edge direction unit for calculating evaluating-values obtained by subtracting said edge direction of the pixels of said first image data form representative edge directions of corresponding pixels and reducing background contrast;

a weighting unit for weighting values calculated from said second image data to said evaluating-value;

a summing unit for summing weighted evaluating-values at each pixel of said second image data;

a scanner for scanning a similarity between said first and second image data to be determined at a plurality of scanning locations where said first and second images data are shifted relative to each other; and

a position detector for detecting a position of said first image data relative to said second image data which produces the highest similarity.