In-focus detecting device

• US 5,396,336 A
• Filed: 10/06/1989
• Issued: 03/07/1995
• Est. Priority Date: 05/16/1986
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Baba, Takeshi, Niwa, Yukichi, Yoshii, Minoru
• Primary Examiner(s): ADAMS JR, RUSSELL E
• Application Number:
  US07/418,576
• Time in Patent Office: 1,978 Days
• Field of Search: 358/227, 354/400, 354/402, 354/195.1
• US Class Current: 348/345
• CPC Class Codes: G02B 7/36 using image sharpness techniques , e.g. image processing techniques for generating autofocus signals image data processing per se G06T; in cameras having a solid state image sensor H04N23/67
• CPC Class Codes: H04N 23/673 based on contrast or high frequency components of image signals, e.g. hill climbing method

Abstract

An in-focus detecting device comprising a photo-electric converter element for converting an object image formed on the image receiving surface thereof through an image forming lens, a drive mechanism for controlling the focusing position of the lens, a focus degree detecting circuit for detecting the degree of focus in a prescribed distance measuring frame of the image receiving surface and the degree of focus outside the frame on the basis of the output signal of the photo-electric converter element, and a control circuit, responsive to the output of the focus degree detecting circuit representing that the degree of focus in the distance measuring frame is below a prescribed level, for comparing the degree of focus in the distance measuring frame with the degree of focus outside the frame to determine the direction of the image forming lens to be driven.

Claims

1. An in-focus detecting device comprising:

(A) a photo-electric converter element for converting an image of an object to be photographed formed on a photo-electric converting surface to an electrical output signal;

(B) driving means arranged to control a relative position of an image forming lens and said photo-electric converter element;

(C) focus degree detecting means for detecting the degree of focus in a distance measuring area set in a prescribed area on said photo-electric converting surface and the degree of focus outside said distance measuring area on said photo-electric converting surface on the basis of the output signal of said photo-electric converter element; and

(D) discriminating means, responsive to detection that the degree of focus in said distance measuring area detected by said focus degree detecting means is lower than a prescribed level, for comparing that degree of focus with the degree of focus outside said distance measuring area on said photo-electric converting surface to determine the direction in which said lens is to be driven.

2. A device according to claim 1, further comprising:

lens drive means for driving said lens on the basis of the determination made by said discriminating means.

3. A device according to claim 1, wherein said photo-electric converter element is an image pickup element.

4. A device according to claim 1, wherein said detecting means detects a width of an edge portion of said object image, and detects said degree of focus on the basis of the value of said width.

5. A device according to claim 4, wherein said detecting means detects the width of said edge portion from the ratio of the gradient of brightness variation of an edge portion of the object image to the brightness difference in said edge portion.

6. A device according to claim 1, wherein said distance measuring area is located at a central portion of the photo-electric converting surface of said photo-electric converter element.

7. A device according to claim 6, wherein the degree of focus outside said distance measuring area is detected from an area on a side of said distance measuring area.

8. A device according to claim 6, wherein the degree of focus outside said distance measuring area is detected from areas on the upper and lower sides of said distance measuring area.

9. A device according to claim 1 or 7, wherein said detecting means includes:

(1) first detecting means for detecting the gradient of the video signal obtained from said photo-electric converter element;

(2) second detecting means for detecting the brightness difference in an edge portion of said video signal;

(3) computing means for computing the width of said edge portion of the object image from the output of said first and said second detecting means; and

(4) peak detecting means for detecting the peak value of the degree of focus on the basis of said width of the edge portion of the object image obtained from said computing means.

10. A device according to claim 9, wherein said computing means includes:

(1) first comparison means for comparing the degree of focus in the distance measuring area obtained from said detecting means with a prescribed level; and

(2) second comparison means, responsive to discrimination of the fact that the degree of focus in said distance measuring area is below the prescribed level by said first comparison means, for comparing the degree of focus in said distance measuring area with the degree of focus outside said distance measuring area.

11. A device according to claim 10, wherein said computing means, responsive to detection that the degree of focus in said distance measuring area is below the prescribed level, determines that a large defocus has occurred, and, if in this state, the degree of focus in said distance measuring area is larger than the degree of focus outside said distance measuring area, controls the lens by a rearward direction of movement of the lens, and if the degree of focus in said distance measuring area is smaller than the degree of focus outside said distance measuring area, controls the lens by a forward direction of movement of the lens.

12. A device according to claim 8, wherein the area outside said distance measuring area comprises an upper area on the upper side of said distance measuring frame and a lower area on the lower side of said distance measuring area, said focus degree detecting means detecting three degrees of focus of said upper area, said lower area and the interior of said distance measuring area respectively, and said discriminating means discriminating the direction in which the lens is to be driven on the basis of such three degrees of focus.

13. A device according to claim 12, wherein said discriminating means includes:

(1) first comparison means for comparing the degree of focus in said distance measuring area with a prescribed level; and

(2) second comparison means for comparing the degree of focus in said upper area with the degree of focus in said lower area.

14. A device according to claim 13, wherein said discriminating means, responsive to detection that the degree of focus in said distance measuring area is below said prescribed level by said first comparing means, determines the direction in which said lens is to be driven on the basis of the comparison of said second comparison means.

15. A device according to claim 14, wherein said discriminating means, responsive to the output of said second comparison means, determines the direction in which said lens is to be driven as forward when the degree of focus of the upper area is larger than the degree of focus of the lower area, or as rearward when the degree of focus of the upper area is smaller than the degree of focus of the lower area.

16. A device according to claim 6, wherein said detecting means detects the width of an edge portion of the object image in each of said plurality of detecting areas and detects the degree of focus in each of said detecting areas on the basis of the value of said width.

17. A device according to claim 16, wherein said detecting means detects the width of the edge portion by detecting the ratio of the gradient of brightness variation of said edge portion of the object image to the brightness difference in said edge portion.

18. An in-focus detecting device comprising:

(A) a photo-electric converter element for converting an image of an object to be photographed formed on the photo-electric converting surface thereof to an electrical output signal;

(B) detecting means for detecting the degree of focus in each of a plurality of detecting areas set in respective prescribed positions on the photo-electric converting surface of said photo-electric converter element; and

(C) control means arrange to discriminate a relative position of an image forming lens and said photo-electric converter element, on the basis of the degree of focus in each of said detecting areas detected by said detecting means, thereby controlling a direction in which a relative distance between said image forming lens and said photo-electric converter element is to be changed.

19. A device according to claim 18, wherein said plurality of detecting areas comprise a detecting area set in a central portion of the photo-electric converting surface of said photo-electric converter element and side detecting areas set on sides of said central detecting area.

20. A device according to claim 18, wherein said plurality of detecting areas comprise a detecting area set in a central portion of the photo-electric converting surface of said photo-electric converter element and upper and lower detecting area set on the upper and lower sides of said central detecting area respectively.

21. A device according to claim 19, wherein said detecting means includes:

(1) first detecting means for detecting the gradient of the video signal obtained by said photo-electric converter element;

(2) second detecting means for detecting the brightness difference in an edge portion of said video signal;

(3) computing means for computing the width of said edge portion of the object image from the output of said first and said second detecting means; and

(4) peak detecting means for detecting the peak value of the degree of focus on the basis of the width of said edge portion of the object image obtained from said computing means.

22. A device according to claim 21, wherein said control means includes:

(1) first comparison means for comparing the degree of focus in the central detecting area obtained from said detecting means with a prescribed level; and

(2) second comparison means for comparing the degree of focus in said central detecting area with the degree of focus in said side detecting areas, whereby when said first comparison means determines that the degree of focus in said central is below the prescribed level, the lens is controlled on the basis of the result of said second comparison means in such a manner that when the degree of focus in said central detecting area is larger than the degree of focus in said side detecting area, the lens is moved rearward, and when the degree of focus in said central detecting area is smaller than the degree of focus in said side detecting area, the lens is moved forward.

23. A device according to claim 20, wherein said detecting means includes:

(1) first detecting means for detecting the gradient of the video signal obtained from said photo-electric converter element;

(2) second detecting means for detecting the brightness difference in an edge portion of said video signal;

(3) computing means for computing the width of said edge portion of the object from the outputs of said first and said second detecting means; and

(4) peak detecting means for detecting the peak value of the degree of focus on the basis of the width of the edge portion of the object image obtained from said computing means.

24. A device according to claim 23, wherein said control means includes:

(1) first comparison means for comparing the degree of focus in said central detecting area with a prescribed level; and

(2) second comparison means for comparing the degree of focus in said upper detecting area with the degree of focus in said lower detecting area, whereby when said first comparison means determines that the degree of focus in said central detecting area is above the prescribed level, the direction of said lens to be driven is controlled in such a manner that if said second comparison means detects that the degree of focus in the upper detecting area is larger than the degree of focus in the lower detecting area, said lens is moved forward, and if it is detected that the degree of focus in the upper detecting area is smaller than the degree of focus in the lower detecting area, said lens is moved rearward.

25. An automatic focus detecting device comprising:

(A) an image pickup element for converting an image of an object to be photographed formed on an image receiving surface thereof through an image forming lens to an electrical output signal;

(B) driving means arranged to vary a relative position between said image forming lens and said image pick-up element, thereby controlling an image forming position of said image forming lens;

(C) position detecting means arranged to compare degrees of focus of respective ones of a plurality of detecting areas including a focus detecting area set on said image receiving surface, thereby detecting the relative position between said image forming lens and said image pick-up element, relative to an in-focus position; and

(D) control means arranged to control said driving means on the basis of a result of detection effected by said position detecting means, when the degree of focus at said focus detecting area is lower than a predetermined level, thereby changing the relative position between said image forming lens and said image pickup element in a direction to obtain an in-focus state of the image of the object in said focus detecting area.

26. A device according to claim 25, wherein said detecting means includes focus degree detecting means for detecting the width of an edge portion of said object image and detecting the degree of focus on the basis of the value of said width.

27. A device according to claim 26, wherein said focus degree detecting means detects the width of said edge portion by detecting the ratio of the gradient of brightness variation of the edge portion of the object image to the brightness difference in said edge portion.

28. A device according to claim 25, wherein said distance measuring frame is set in a central portion of the entire area of said image receiving surface.

29. A device according to claim 28, wherein the degree of focus in an area outside said distance measuring frame is detected from either the left and right hand sides or upper and lower sides of said distance measuring frame.

30. A focus detecting device, comprising:

(A) image pickup means for converting an image of an object to be photographed formed on an image receiving plane into an electrical signal, thereby outputting an image pickup signal;

(B) detecting means for detecting a degree of focus on each of a plurality of areas set on said image receiving plane, including a central area and its surrounding areas on said image receiving plane, on the basis of said image pickup signal; and

(C) control means for executing arithmetical operations on informations concerning the respective degrees of focus of said central area and its surrounding areas detected by said detecting means and for effecting the focus of control on the basis of the result of the arithmetical operations.

31. A focus detecting device according to claim 30, further comprising:

(D) a photographing lens for focusing the image of the object onto said image receiving plane; and

(E) driving means for varying a relative position between said photographing lens and said image receiving plane.

32. A focus detecting device according to claim 30, wherein said control means is arranged to detect an in-focus state of the object and its background, on the basis of the degrees of focus of said plurality of areas.

33. a focus detecting device according to claim 30, wherein said plurality of areas include a central area set at a center of said image receiving plane and areas set at right and left sides of said central area.

34. A focus detecting device according to claim 30, wherein said plurality of areas include a central area set at a center of said image receiving plane and areas set at upper and lower sides of said central area.

35. A focus detecting device according to claim 30, wherein said control means is arranged to operate said driving means, depending upon the result of the detection effected by said detecting means, thereby controlling a direction in which the relative position between said photographing lens and said image pickup means is to be changed.

36. A focus detecting device according to claim 30, wherein said detecting means is arranged to detect a degree of focus by detecting a width of an edge portion of an object to be photographed, at each of said plurality of areas.

37. A focus detecting device according to claim 30, wherein said control means is arranged to decide a direction in which the lens is to be driven, on the basis of the degrees of focus at said plurality of areas, when the degree of focus at said central area is lower than a predetermined level.

38. A focus detecting device according to claim 30, wherein said control means is arranged to effect focus control, on the basis of the degree of focus at said central area, when the degree of focus at said central area is higher than said predetermined level.

39. A focus detecting device, comprising:

(A) image pickup means for converting an image of an object to be photographed formed on an image receiving surface into an electrical signal, thereby outputting an image pickup signal;

(B) gate means for extracting signals corresponding to a plurality of areas, respectively, set on said image receiving plane, including a central area and its surrounding areas, from said image pickup signal; and

(C) detecting means for detecting a degree of focus at each of said plurality of areas, on the basis of the image pickup signals corresponding to said plurality of areas, respectively, which were extracted by said gate means, said detecting means being arranged to evaluate the respective degrees of focus of said plurality of areas, to detect the de-focus state relative to the object.

40. A focus detecting device according to claim 39, further comprising:

(D) a photographing lens for forming the image of the object to be photographed onto said image forming plane;

(E) driving means for varying a relative position between said photographing lens and said image receiving plane; and

(F) control means arranged to decide a direction in which the photographic lens is to be driven, in response to an output of said detecting means, thereby controlling said driving means.

41. A focus detecting device according to claim 39, wherein said control means is arranged to detect an in-focus state of the object and its background, on the basis of the degrees of focus of said plurality of areas.

42. A focus detecting device according to claim 39, wherein said plurality of areas include a central area set at a center of said image receiving plane and areas set at right and left sides of said central area.

43. A focus detecting device according to claim 41 or 42, wherein said control means is arranged to decide a direction in which the lens is to be driven, on the basis of the degrees of focus at said plurality of areas, when the degree of focus at said central area is lower than a predetermined level.

44. A focus detecting device according to claim 43, wherein said control means is arranged to effect focus control, on the basis of the degree of focus at said central area, when the degree of focus at said central area is higher than said predetermined level.

45. A focus detecting device according to claim 39, wherein said detecting means is arranged to detect a degree of focus by detecting a width of an edge portion of an object to be photographed, at each of said plurality of areas.

46. A focus detecting device comprising:

(A) an image pickup means for converting an image of an object to be photographed formed on a photo-electric converting plane to an image signal;

(B) extracting means for extracting image signals corresponding to a plurality of detecting areas set on said photo-electric converting plane, including a central area and its surrounding areas, from said image signal;

(C) detecting means for respectively detecting a degree of focus on each of said detecting areas on the basis of the signal extracted by said extracting means; and

(D) deciding means arranged to decide respective degrees of focus os said object to be photographed on said photo-electric converting plane and a background of said object, on the basis of a result of detection effected by said detecting means.

47. A focus detecting device according to claim 46, wherein said control means is arranged to detect an in-focus state of the object and its background, on the basis of the degrees of focus of said plurality of areas.

48. A focus detecting device according to claim 47, wherein said plurality of areas include a central area set at a center of said image receiving plane and areas set at right and left sides of said central area.

49. A focus detecting device according to claim 47, wherein said plurality of areas include a central area set at a center of said image receiving plane and areas set at upper and lower sides of said central area.