Exposure control device

• US 5,272,538 A
• Filed: 09/13/1990
• Issued: 12/21/1993
• Est. Priority Date: 11/04/1987
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Fujiwara, Akihiro, Suda, Hirofumi, Imai, Kunio, Toyama, Masamichi, Homma, Hideo, Yamada, Kunihiko
• Primary Examiner(s): BRINICH, STEPHEN M
• Application Number:
  US07/582,798
• Time in Patent Office: 1,195 Days
• Field of Search: 358/125-126, 358/228, 358/211, 358/213.19
• US Class Current: 348/362
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 23/75 by influencing optical camera components

Abstract

An exposure control device for performing exposure control on the basis of a video signal obtained from a light measuring area set within an image sensing plane is provided with a determining circuit which determines the position of a photographed object within the image sensing plane from the values of a specific component of the video signal obtained from the inside and outside of a detection area the position of which is variably set within the image sensing plane. The light measuring area is set in the object'"'"'s position within the image sensing plane detected by the determining circuit. The exposure control device is provided further with a changing circuit which detects the size of the object on the image sensing plane and changes the size of the light measuring area accordingly, and a weighting circuit which performs for light measurement a weighting operation on video signals obtained from the inside and outside of the light measuring area.

Claims

1. An exposure control device comprising:

a) computing means for computing information on a difference in a specific component between video signals obtained from the inside and outside of a detection area which is set to be shiftable within an image sensing plane;

b) determining means for determining the position of the detection area in said image sensing plane on the basis of said difference information obtained by said computing means;

c) light measuring area setting means for setting a light measuring area at the position of the detection area determined by said determining means; and

d) light measuring means for performing light measurement on the basis of said light measuring area set by said light measuring area setting means.

2. A device according to claim 1, wherein said light measuring area setting means is arranged to set said light measuring area at a position where said difference in said specific component obtained by said computing means between the inside and outside of said detection area becomes a maximum value.

3. A device according to claim 2, wherein said computing means is arranged to obtain information on a difference in a luminance level between video signals obtained from the inside and outside of said detection area.

4. A device according to claim 2, wherein said computing means is arranged to obtain information on a difference in a high frequency component between video signals obtained from the inside and outside of said detection area.

5. A device according to claim 2, wherein said light measuring area is used also as said detection area.

6. A device according to claim 2, wherein said determining means is arranged to shift the position of said detection area within said image sensing plane to changed positions in accordance with a given algorithm and to obtain said difference in said specific component.

7. A device according to claim 6, wherein said determining means is arranged to shift said detection area to a given extent at a time in a wobbling manner upward, downward, to the left and to the right in a given order.

8. A device according to claim 1, further comprising exposure control means for controlling an exposed state on the basis of an output of said light measuring means.

9. An exposure control device comprising:

a) computing means for computing information on a difference in a specific component between video signals obtained from the inside and outside of a detection area which is set in a variable size on an image sensing plane;

b) determining means for determining the size of the detection area within said image sensing plane on the basis of the difference information obtained by said computing means;

c) light measuring area setting means for setting the size of a light measuring area according to the size of the detection area determined by said determining means; and

d) light measuring means for performing light measurement on the basis of said light measuring area set by said light measuring area setting means.

10. A device according to claim 9, wherein said determining means is arranged to determine the size of said object from the size of said detection area which is obtained when an output of said computing means becomes a maximum value.

11. A device according to claim 10, wherein said specific component is a luminance level of a video signal.

12. A device according to claim 10, wherein said specific component is a high-frequency component level of a video signal.

13. A device according to claim 10, wherein said light measuring area is used also as said detection area.

14. A device according to claim 10, wherein said determining means is arranged to vary the size of said detection area on said image sensing plane in accordance with a given algorithm and to fetch the difference in said specific component at every one of varied sizes of said detection area.

15. A device according to claim 14, wherein said determining means is arranged to fetch said difference information obtained every time the size of said detection area is changed, for example, stepwise to a large size, a medium size and a smaller size in three steps from one over to another.

16. A device according to claim 15, wherein said light measuring area setting means is arranged to select one of the three different sizes of said detection area at which said difference information produced from said computing means becomes a maximum value and to set said light measuring area at said detection area having said one of the three sizes.

17. An exposure control device comprising:

a) setting means for setting a detection area which is arranged to have the position and the size thereof variable within an image sensing plane;

b) first determining means for determining the position of the detection area on said image sensing plane by computing information on a difference in a specific component between video signals obtained from the inside and outside of said detection area;

c) second determining means for determining the size of the detection area on said image sensing plane by computing information on a difference in a specific component between video signals obtained from the inside and outside of said detection area; and

d) light measuring area control means for controlling either or both of the position and the size of said detection area within said image sensing plane on the basis of the results of determination made by said first and second determining means.

18. A device according to claim 17, wherein said first determining means is arranged to determine the position of the object on the basis of one of the varied positions of said detection area in which said difference in said specific component becomes a maximum value.

19. A device according to claim 17, wherein said second determining means is arranged to determine the size of the object on the basis of one of the varied sizes of said detection area at which said difference in said specific component becomes a maximum value.

20. A device according to claim 18, wherein said light measuring area control means is arranged to adjust the position of said light measuring area to that of the object determined by said first determining means.

21. A device according to claim 19, wherein said light measuring area control means adjusts the size of said light measuring area to that of the object determined by said second determining means.

22. A device according to claim 20, wherein said first determining means is arranged to shift the position of said detection area within said image sensing plane to varied positions in accordance with a given algorithm and to obtain said difference in said specific component.

23. A device according to claim 22, wherein said first determining means is arranged to shift said detection area to a given extent at a time in a wobbling manner upward, downward, to the left and to the right in a given order.

24. A device according to claim 21, wherein said second determining means is arranged to vary the size of said detection area on said image sensing plane in accordance with a given algorithm and to fetch the difference in said specific component at every one of varied sizes of said detection area.

25. A device according to claim 24, wherein said second determining means is arranged to fetch said difference information obtained every time the size of said detection area is changed, for example, stepwise to a large size, a medium size and a smaller size in three steps from one over to another.

26. A device according to claim 25, wherein said light measuring area setting means is arranged to select one of the three different sizes of said detection area at which said difference information produced from said computing means becomes a maximum value and to set said light measuring area at said detection area having said one of the three sizes.

27. A device according to claim 17, wherein said specific component is a luminance level of a video signal.

28. A device according to claim 17, wherein said specific component is a high-frequency component level of a video signal.

29. A device according to claim 17, wherein said light measuring area is used also as said detection area.

30. An exposure control device comprising:

a) computing means for computing information on a difference in a specific component between video signals obtained from the inside and outside of a detection area which is set to be shiftable within an image sensing plane;

b) determining means for determining the position of the detection area within said image sensing plane on the basis of said difference information obtained by said computing means at different positions of said detection area;

c) light measuring area setting means for setting a light measuring area at the position of the detection area determined by said determining means;

d) light measuring means for performing light measurement on the basis of said light measuring area set by said light measuring area setting means;

e) exposure detecting means for detecting exposure information for the inside of said light measuring area and for an area other than said light measuring area or the full area including said light measuring area; and

f) exposure control means for producing exposure control information which is obtained by performing a given weighting operation on an output of said exposure detecting means on the basis of levels of said specific component of video signals obtained from the inside and outside of said light measuring area.

31. A device according to claim 30, wherein said light measuring area setting means is arranged to set said light measuring area at a position where said difference in said specific component obtained by said computing means between the inside and outside of said detection area becomes a maximum value.

32. A device according to claim 31, wherein said computing means is arranged to obtain information on a difference in a luminance level between video signals obtained from the inside and outside of said detection area.

33. A device according to claim 31, wherein said computing means is arranged to obtain information on a difference in a high frequency component between video signals obtained from the inside and outside of said detection area.

34. A device according to claim 31, wherein said light measuring area is used also as said detection area.

35. A device according to claim 31, wherein said determining means is arranged to shift the position of said detection area within said image sensing plane to varied positions in accordance with a given algorithm and to obtain said difference in said specific component.

36. A device according to claim 35, wherein said determining means is arranged to shift said detection area to a given extent at a time in a wobbling manner upward, downward, to the left and to the right in a given order.

37. A device according to claim 30, wherein said exposure control means is arranged to produce an exposure control signal by mixing an exposure information signal obtained from the inside of said light measuring area and another exposure information signal obtained from the outside of said light measuring area or the full area.

38. A device according to claim 37, wherein said exposure control means is arranged to perform a weighting operation on exposure information obtained from the inside and outside of said light measuring area by changing either a mixing ratio or gains of said exposure information signals.

39. An exposure control device comprising:

a) setting means for movably setting a detection area in an image sensing plane of an image sensing means which converts an image formed on the image sensing plane to an electric image signal;

b) detecting means for detecting levels of a predetermined component of the image signal inside and outside of the detection area;

c) control means for controlling the setting means so as to change a position and/or size of the detection area in the image sensing plane; and

d) exposure control means for controlling an exposure on the basis of the predetermine component.

40. A device according to claim 39, wherein said control means controls said setting means so that said setting means sets the detection area at a position where the difference in said predetermined component detected by said detecting means between the inside and the outside of the detection area becomes a maximum value.

41. A device according to claim 40, wherein said predetermined component is a level of a luminance signal or a level of a high frequency component signal in the image signal.

42. A device according to claim 39, wherein said control means controls said setting means to change the size of the detection are so that the difference in said predetermined component detected by said detecting means between the inside and the outside of the detection area becomes a maximum value.

43. A device according to claim 39, 41 or 42, wherein said exposure control discriminates a condition of the image on the basis of a difference in levels of said predetermined component inside and outside of said detection area detected by said detecting means and outputs an exposure control signal after applying predetermined weights to said predetermined component signal of the inside and the outside of said predetermined detection area, respectively.

44. An exposure control device, comprising:

a) setting means for movably setting a detection area in an image sensing plane of an image sensing means which converts an image formed on the sensing plane to an electric image signal;

b) control means for controlling said setting means to change a set position and/or a size of said detection area on said image sensing plane in accordance with a change of the image of an object focused on said image sensing plane; and

c) exposure control means for controlling an exposure on the basis of a predetermined component of the image signal inside and outside of the detection area.

45. A device according to claim 44, wherein said predetermined component is a level of a luminance signal included in said image signal.

46. A device according to claim 44, wherein said control means changes a position and/or a size of said detection area so that a difference in level of said predetermined component inside and outside of said detection area becomes a maximum.

47. A device according to claim 45, wherein said exposure control means produces an exposure control signal on the basis of a luminance signal in said image signal, by discriminating a condition of an image of a signal from a difference in levels of luminance signals of the inside and the outside of said detection area and applying predetermined weights tot he luminance signal levels of the inside and the outside of said detection area, thereby producing the exposure control signal.

48. A device according to claim 47, wherein said exposure control means discriminates "back-lighting" or "front-lighting" of the picture image and controls the weights applied to the luminance signal of the inside and the outside of said detection area in accordance with a result of such discrimination.

49. A device according to claim 47, wherein said exposure control means is arranged to perform a weighting operation on exposure information obtained from the inside and the outside of said detection area by changing either a mixing ratio or gains of exposure information signals.