Automatic exposure control apparatus

• US 5,353,058 A
• Filed: 08/12/1992
• Issued: 10/04/1994
• Est. Priority Date: 10/31/1990
• Status: Expired due to Term

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Takei, Hirofumi
• Primary Examiner(s): Oberley, Alvin E.
• Assistant Examiner(s): HARVEY, MINSUN OH
• Application Number:
  US07/927,739
• Time in Patent Office: 783 Days
• Field of Search: 358/41, 358/228, 358/29 C, 358/55, 348/362, 348/364, 348/242, 348/363
• US Class Current: 348/363
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 23/75 by influencing optical camera components

Abstract

Disclosed is an automatic exposure control apparatus so adapted that a photographic subject such as a human being can be photographed appropriately even if the subject is backlighted or excessively front-lighted. The control apparatus divides a frame into a plurality of areas and detects the backlighted state or excessively front-lighted state based upon the luminance of each of these areas. In case of backlighting or excessive front-lighting, an exposure correction of the entire frame is performed in conformity with the luminance of an area in which a flesh color is present in the vicinity of the center of the frame.

Claims

1. An automatic exposure control apparatus comprising:

photometric means for performing photometry using a signal indicative of a photometric area set at a predetermined position within a frame;

discriminating means for discriminating photographic conditions of a subject by detecting and evaluating levels of luminance components and levels of chromaticity components in a video signal in respective ones of a plurality of divided areas set within the frame; and

correcting means for correcting a photometric control signal of said photometric means in dependence upon results of discrimination performed by said discriminating means.

2. The apparatus according to claim 1, wherein said correcting means retrieves one divided area, which has a chromaticity component of a predetermined level, from among the plurality of divided areas, and corrects the photometric control signal using the luminance level of the retrieved divided area as the luminance of the subject.

3. The apparatus according to claim 1, wherein said discriminating means comprises:

first evaluating means for evaluating the lighting of the subject to determine at least whether it is in an ordinary state or an abnormal state;

second evaluating means for evaluating the subject to determine whether it possesses a portion having a specific color; and

means for discriminating the photographic state of the subject based upon evaluation information from said first and second evaluating means;

wherein when it is discriminated by said discriminating means that the photographic state of the subject is a lighting state which is the abnormal state and that the subject possesses a portion having the specific color, said correcting means supplies said photometric means with correction information in such a manner that a detection area which includes the portion having the specific color becomes becomes the appropriate exposure.

4. The apparatus according to claim 3, wherein the abnormal state is a backlighted state or excessively front-lighted state.

5. The apparatus according to claim 3, wherein said specific color is a flesh color.

6. The apparatus according to claim 3, wherein said discriminating means judges whether said specific color is in the vicinity of the center of the frame.

7. The apparatus according to claim 1, wherein said discriminating means detects the level of the luminance component in a subject area within the imaged frames and in a peripheral area of the subject area based upon a distribution of the level of luminance component in the video signal, and evaluates the lighting of the subject using difference information indicative of the difference between the level of the luminance component in the subject area and the level of the luminance component in the peripheral area, and ratio information indicative of the level of the luminance component in the subject area to the level of the luminance component in the peripheral area.

8. The apparatus according to claim 1, wherein sizes of divided areas set in order to detect the levels of the chromaticity components are set to be smaller than the sizes of divided areas set in order to detect the levels of the luminance components.

9. An automatic exposure control apparatus comprising:

imaging means for converting an image of a subject produced on an image plane into a multi-component electric signal and outputting the electric signal as an image signal;

first detection means for detecting a predetermined signal component in the image signal;

second detection means for detecting a luminance signal component in the image signal;

determination means for determining a photographing condition for the image signal based on an output of said second detection means;

photometric area setting means for setting a photometric area within the image frame based on the outputs of said first detection means and said determination means; and

exposure control means for performing an exposure control based on the luminance signal component of the image signal which exists within the photometric area set by said photometric area setting means.

10. The apparatus according to claim 9, wherein the predetermined signal component comprises color signal information of the image signal.

11. The apparatus according to claim 10, wherein said second detection means detects a luminance level of the image signal.

12. The apparatus according to claim 11, wherein said first detection means discriminates an area having predetermined color signal information from a plurality of areas within the image frame divided in accordance with a first pattern.

13. The apparatus according to claim 12, wherein if said first detection means cannot detect an area in which the predetermined color signal information exists, said photometric area setting means sets a photometric area a luminance level of which is the lowest among the areas divided in accordance with the second pattern.

14. The apparatus according to claim 13, wherein said exposure control means performs an exposure control by controlling a diaphragm of the imaging means and changing a gain of the control so that an appropriate luminance level within the photometric area can be obtained.

15. The apparatus according to claim 12, wherein said photometric area setting means designated to set a photometric area from a plurality of areas within the image frame divided in accordance with a second pattern, said photometric area including the area detected by said first detection means out of which the predetermined color signal information has been detected.

16. The apparatus according to claim 15, wherein said exposure control means performs an exposure control by controlling a diaphragm of the imaging means and a changing a gain of the control so that an appropriate luminance level with in the photometric area can be obtained.

17. The apparatus according to claim 15, wherein the first pattern is finer than the second pattern.

18. An automatic exposure control apparatus comprising:

first division means for dividing an image frame into a first plurality of areas in accordance with a first pattern, each area including an image signal;

second division means for dividing the frame into a second plurality of areas in accordance with a second pattern, each area including an image signal;

first discrimination means for discriminating a state of the frame based on a luminance signal component of the image signals of the first plurality of areas;

second discrimination means for discriminating an area out of which a predetermined signal component is detected from the second plurality of areas;

photometric area designating means for designating a photometric area from the first plurality of areas based on the discrimination results of at least said first discrimination means; and

exposure control means for performing an exposure control based on the image signal of the photometric area designated by said photometric area designating means.

19. The apparatus according to claim 18, wherein the first discrimination means detects a luminance level of an image of a subject produced on the frame.

20. The apparatus according to claim 19, wherein said first discrimination means discriminates whether, the frame is normal, back-lighted, or excessively front-lighted, based on the respective luminance signals of the first plurality of areas.

21. The apparatus according to claim 18, wherein the predetermined signal component is color signal information of the image of the subject produced on the frame.

22. The apparatus according to claim 21, wherein the color signal information is color information related to a human being.

23. The apparatus according to claim 18, wherein, if the state of the frame is discriminated to be either back-lighted or excessively front-lighted by said first discrimination means, said photometric area designating means selects the photometric area based on the discrimination results by said second discrimination means.

24. The apparatus according to claim 23, wherein, if said second discrimination means cannot discriminate an area out of which the predetermined signal component is detected, said photometric area designated means selects the photometric area based on the discrimination results by said first discrimination means.

25. The apparatus according to claim 24, wherein, if said second discrimination means cannot discriminate an area out of which the predetermined signal component is detected, said photometric area designating means selects a photometric area the luminance level of which is the lowest among the first plurality of areas based on the discrimination results by said first discrimination means.

26. An imaging apparatus comprising:

imaging means for converting an image of a subject produced on an image frame into an electric signal and outputting the electric signal as an image signal;

first detection means for detecting a luminance signal component from the image signals of a first plurality of areas within the frame divided in accordance with a first pattern;

second detection means for detecting a predetermined signal component from the image signals of a second plurality of areas of the frame divided in accordance with a second pattern; and

control means for setting a detection area within the frame based on outputs of said first and second detection means.

27. The apparatus according to claim 26, wherein said first detection means detects a luminance level of image signal obtained by the imaging means.

28. The apparatus according to claim 27, wherein said second detection means detects a predetermined color signal information in an image signal obtained by the imaging means.

29. The apparatus according to claim 28, wherein, if the detection area based on the output of said second detection means cannot be set, said control means sets the detection area based on the output of said first detection means.

30. The apparatus according to claim 29, wherein, in a case where said first detection means detects the state of the image frame and where the detected state of the frame is back-lighted or excessively front-lighted, said control means designates an area in which the predetermined color signal information exists based on the output of said second detection means and sets the detection area in the designated area, while if said second detection means cannot designate an area in which the predetermined color signal information exists, said control means sets an area where the luminance level is the lowest among the first plurality of areas based on the output of said first detection means, as a detection area.

31. The apparatus according to claim 27, wherein said control means discriminates a state of the image frame based on the output of said first detection means, and in response sets the detection area using the output of said second detection means.

32. The apparatus according to claim 26, wherein the detection area is a photometric area.

33. An imaging apparatus comprising:

imaging means for converting an image of a subject produced in an image frame into an electric signal and outputting the electric signal as an image signal;

area division means for dividing the frame into a plurality of areas;

discriminating means for discriminating luminance signal information and color signal information in the image signal in the areas; and

correction means for correcting the exposure based on the output of said discriminating means, wherein the output is based on luminance signal information and color signal information in the image signal.

34. The apparatus according to claim 33, wherein said area division means divides the image frame into a first plurality of areas in accordance with a first pattern, and wherein said discriminating means discriminates luminance levels of the respective areas and discriminates the state of the frame on the basis of the discriminated levels.

35. The apparatus according to claim 34, wherein said division means divides the frame into a second plurality of areas in accordance with a second pattern, and wherein said discriminating means discriminates an area in which the predetermined color signal information exists.

36. The apparatus according to claim 35, wherein, if the frame is discriminated as back-lighted or excessively front-lighted, said discriminating means sets the discriminated area in which the predetermined color signal information exists as an exposure correction area, and if said discriminating means cannot discriminate an area in which the predetermined color signal information exists, and discriminating means sets an area where the luminance level is the lowest among the second plurality of areas as an exposure correction area.

37. The apparatus according to claim 36, said correction means includes a control means for controlling a diaphragm and gain of the imaging means, and corrects an exposure so that the exposure correction area can be appropriately exposed.

38. A video camera apparatus comprising:

imaging means for converting an image of a subject produced on an image frame into a multi-component electric signal and outputting the electric signal as an image signal;

first detection means for detecting a luminance signal component in the image signal;

second detection means for detecting a predetermined signal component in the image signal;

photometric area setting means for setting a photometric area within the image frame based on the outputs of said first detection means and said second detection means; and

exposure control means for performing an exposure control based on a luminance signal component in the image signal which exists within the photometric area set by said photometric area setting means.

39. The apparatus according to claim 38, wherein said second detection means detects a color signal out of the image signal.

40. The apparatus according to claim 38, further comprising determination means for determining a photographing condition for the image signal on the basis of an output of said first detection means.

41. The apparatus according to claim 40, wherein said image frame is divided into a plurality of areas, and wherein said first detection means detects a luminance level of a luminance signal within each area.

42. The apparatus according to claim 41, wherein said image frame is divided into a plurality of areas, and wherein said second detection means detects a level of a color signal within each area.

43. The apparatus according to claim 42, wherein said determination means determines whether a photographing condition for the image signal is normal, back-lighted, or excessively front-lighted.

44. The apparatus according to claim 43, wherein when the photographing condition is back-lighted or excessively front-lighted, said photometric area setting means sets the photometric area based on the output of said second detection means.

45. The apparatus according to claim 38, wherein said exposure control means controls the diaphragm or gain of the apparatus so that a proper exposure condition is obtained.