Image sensing apparatus having automatic focusing function for automatically matching focus in response to video signal

• US 5,003,339 A
• Filed: 02/14/1990
• Issued: 03/26/1991
• Est. Priority Date: 05/11/1988
• Status: Expired due to Term

• Current Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Kikuchi, Kenichi, Takuma, Masao, Haruki, Toshinobu
• Primary Examiner(s): Adams, Russell E.
• Application Number:
  US07/481,745
• Time in Patent Office: 405 Days
• Field of Search: 354/400, 354/402, 358/227
• US Class Current: 396/100
• CPC Class Codes: H04N 23/673 based on contrast or high frequency components of image signals, e.g. hill climbing method

Abstract

In a video camera having an automatic focusing function, a first sampling area in the center of an image sensed picture and a second sampling area around the first sampling area are set. Considering a case in which an auto-focus operation is carried out selecting the first sampling area as a focusing area, when the difference between the newest focus evaluating value and the maximum focus evaluating value becomes one-eighth or more of the maximum focus evaluating value, the second sampling area is selected as the focusing area, to carry out an auto-focus operation. Consequently, an auto-focus operation conforming to the state of an object is carried out. In addition, a priority area for exposure control is selected following selection of the focusing area. Thus, exposure relative to a main object is always maintained most suitably. Furthermore, even if the focus evaluating value has no distinct peak, the erroneous detection of the in-focus position can be prevented since the sampling area having a larger maximum value per unit area is selected as a focusing area.

Claims

1. An image sensing apparatus for automatically matching the focus relative to an object, comprising:

image sensing means (2,

     8) having a focusing lens and an image sensor for generating a video signal in response to light incident from said object,

relative position changing means (3,

     4) for changing a relative position in the direction of an optical axis of said focusing lens relative to said image sensor,

sampling area setting means (13,

     15) for setting a first sampling area located in the center of an image sensed picture and a second sampling area including said first sampling area and having a larger area than that of said first sampling area by time division of said video signal,

focus evaluating value detecting means (9, 10, 13, 4, 16,

     17) for detecting every constant time period a level of a high frequency component in a video signal in each of said first and second sampling areas to supply the same as a focus evaluating value in the corresponding sampling area,

each of the focus evaluating values taking the maximum value in an in-focus position,

means (26) for selecting either one of said first and second sampling areas as a focusing area according to a relative relation between the newest value of the focus evaluating value in each of said first and second sampling areas and a variable reference value calculated based on the previous focus evaluating value in the corresponding sampling area, and

control means (26,

     27) for controlling said relative position changing means based on a focus evaluating value corresponding to the sampling area selected as said focusing area so as to drive the relative position of said focusing lens to a position where the focus evaluating value becomes the maximum value.

2. The image sensing apparatus according to claim 1, wherein said focusing area selecting means comprises

means for calculating said variable reference value based on the maximum value of the previous focus evaluating value in said corresponding sampling area.

3. The image sensing apparatus according to claim 2, wherein said focusing area selecting means comprises

means for selecting a focusing area depending on which of the difference between the newest focus evaluating value and the maximum value of the previous focus evaluating value in said corresponding sampling area and said variable reference value is larger.

4. The image sensing apparatus according to claim 3, wherein said variable reference value is a value which is one-n-th (n:

positive integer) of the maximum value of the previous focus evaluating value in said corresponding sampling area.

5. The image sensing apparatus according to claim 4, wherein said variable reference value is a value which is one-eight of the maximum value of the previous focus evaluating value in said corresponding sampling area.

6. The image sensing apparatus according to claim 3, wherein said focusing area selecting means comprises

means for switching focusing areas when the difference between said newest focus evaluating value and the maximum value of the previous focus evaluating value exceeds said variable reference value.

7. The image sensing apparatus according to claim 1, wherein said focus evaluating value detecting means comprises

first filter means for extracting a level of a first high frequency component in said video signal,

second filter means for extracting a level of a second high frequency component including a component at a frequency which is lower than the frequency of said first high frequency component,

means for alternately selecting outputs of said first and second filter means every said constant time period, and

means for accumulating every said first and second sampling areas the level of the first or second high frequency component in said video signal extracted by said first or second filter means.

8. The image sensing apparatus according to claim 1, wherein said focusing area selecting means makes selection after the relative position of said focusing lens is driven once to the position where said focus evaluating value becomes the maximum value.

9. An image sensing apparatus for automatically matching the focus relative to an object, comprising:

image sensing means (2,

     8) having a focusing lens and an image sensor for generating a video signal in response to light incident from said object,

relative position changing means (3,

     4) for changing a relative position in the direction of an optical axis of said focusing lens relative to said image sensor,

sampling area setting means (13,

     15) for setting a first sampling area located in the center of an image sensed picture and a second sampling area including said first sampling area and having a larger area than that of said first sampling area by time division of said video signal,

focus evaluating value detecting means (9, 10, 13, 14, 16,

     17) for detecting every constant time period a level of a high frequency component in a video signal in each of said first and second sampling areas to supply the same as a focus evaluating value in the corresponding sampling area,

each of the focus evaluating values taking the maximum value in an in-focus position,

means (26) for selecting either one of said first and second sampling areas as a focusing area,

first control means (26) for controlling said relative position changing means based on a focus evaluating value corresponding to the sampling area selected as said focusing area so as to drive the relative position of said focusing lens to a position where the focus evaluating value takes the maximal value having a predetermined projected amount as compared with focus evaluating values in relative positions of focusing lens before and after said position of said focusing lens, and

second control means (26) for comparing the respective maximum values of the focus evaluating values in said first and second sampling areas per unit area when the focus evaluating value corresponding to said selected sampling area does not take said maximal value and controlling said relative position changing means so as to fix the relative position of said focusing lens to a position where the focus evaluating value in the sampling area having the larger maximum value reaches a maximum.

10. The image sensing apparatus according to claim 9, wherein said focusing area selecting means comprises

means for selecting either one of said first and second sampling areas as a focusing area according to a relative relation between the newest value of said focus evaluating value in each of said first and second sampling areas and a variable reference value calculated based on the previous focus evaluating value in the corresponding sampling area.

11. The image sensing apparatus according to claim 9, wherein said focus evaluating value detecting means comprises

first filter means for extracting a level of a first high frequency component in said video signal,

second filter means for extracting a level of a second high frequency component including a component at a frequency which is lower than the frequency of said first high frequency component,

means for alternately selecting outputs of said first and second filter means every said constant time period, and

means for accumulating every said first and second sampling areas the level of the first or second high frequency component in said video signal extracted by said first or second filter means.

12. An image sensing apparatus for automatically matching the focus and the exposure relative to an object, comprising:

image sensing means (2,

     8) having a focusing lens and an image sensor for generating a video signal in response to light incident from said object,

relative position changing means (3,

     4) for changing a relative position in the direction of an optical axis of said focusing lens relative to said image sensor,

means (6,

     7) for changing exposure relative to said object,

means (13,

     15) for setting a plurality of sampling areas divided on an image sensed picture by time division of said video signal,

focus evaluating value detecting means (9, 10, 13, 14, 16-21) for detecting every constant time period a level of a high frequency component in a video signal in each of said plurality of sampling areas to supply the same as a focus evaluating value in the corresponding sampling area,

each of the focus evaluating values taking the maximum value in an in-focus position,

exposure evaluating value detecting means (11, 13, 14, 16-21) for detecting every constant time period a level of a luminance signal in the video signal in each of said plurality of sampling areas to supply the same as an exposure evaluating value in the corresponding sampling area,

first selecting means (26) for selecting any one of said plurality of sampling areas as a focusing area,

first control means (26) for controlling said relative position changing means based on a focus evaluating value corresponding to the sampling area selected as said focusing area so as to drive the relative position of said focusing lens to a position where the focus evaluating value becomes the maximum value,

second selecting means (26) for selecting as a priority area for exposure control the sampling area selected by said first selecting means, and

second control means (26) for controlling said exposure changing means such that the exposure evaluating value corresponding to the sampling area selected as said priority area coincides with a predetermined target level.

13. The image sensing apparatus according to claim 12, which further comprises means for determining based on the exposure evaluating value in each of said plurality of sampling areas whether or not an abnormal luminance portion exists in the corresponding sampling area, and

said second selecting means selects as said priority area the sampling area selected by said first selecting means only when said determining means determines that no abnormal luminance portion exits.

14. The image sensing apparatus according to claim 13, wherein said plurality of sampling areas comprises at least a first sampling area located in the center of the image sensed picture, a second sampling are including said first sampling area and having a larger area than that of said first sampling area and a third sampling area defined by excluding said first sampling area from said second sampling area.

15. The image sensing apparatus according to claim 14, wherein said second selecting means comprises

means for selecting said first sampling area as the priority area if no abnormal luminance portion exists in said first sampling area while selecting said second sampling area as the priority area if an abnormal luminance portion exists, when said first sampling area is selected as said focusing area, and

means for selecting said second sampling area as the priority area if no abnormal luminance portion exists in said second sampling area while supplying the average value of exposure evaluating values in the remaining sampling areas where no abnormal luminance portion exists to said second control means as an exposure evaluating value in the priority area if an abnormal luminance portion exists, when said second sampling area is selected as said focusing area.

16. The image sensing apparatus according to claim 14, wherein said focusing area selecting means comprises

means for selecting either one of said first and second sampling areas as a focusing area according to a relative relation between the newest value of said focus evaluating value in each of said first and second sampling areas and a variable reference value calculated based on the previous focus evaluating value in the corresponding sampling area.