Digital camera

• US 20070030381A1
• Filed: 01/03/2006
• Published: 02/08/2007
• Est. Priority Date: 01/18/2005
• Status: Active Grant

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Maeda, Toshiaki
• Granted Patent: US 7,791,668 B2
• Time in Patent Office: Days
• US Class Current: 348/345
• CPC Class Codes: G02B 7/282 Autofocusing of zoom lenses
• CPC Class Codes: G03B 13/36 Autofocus systems
• CPC Class Codes: H04N 2101/00 Still video cameras
• CPC Class Codes: H04N 23/61 based on recognised objects
• CPC Class Codes: H04N 23/611 where the recognised objects include parts of the human body
• CPC Class Codes: H04N 23/635 Region indicators; Field of view indicators
• CPC Class Codes: H04N 23/673 based on contrast or high frequency components of image signals, e.g. hill climbing method
• CPC Class Codes: H04N 23/675 comprising setting of focusing regions

Abstract

A digital camera includes: an image-capturing unit that receives light transmitted through a photographic optical system and outputs image signals; a lens drive unit that moves a focus lens constituting the photographic optical system along an optical axis; an evaluation value calculation unit that calculates a focal point evaluation value that changes in correspondence to a position assumed by the focus lens based upon the image signals; a focal adjustment unit that executes an AF search by repeatedly engaging the image-capturing unit and the evaluation value calculation unit in operation as the focus lens is made to move along the optical axis by the lens drive unit, detecting a focus match position based upon resulting focal point evaluation values and driving the focus lens to the focus match position; a face recognition unit that recognizes a face of a person in an image by analyzing the image signals; a distance calculation unit that determines an approximate distance to the face based upon the size of the recognized face; and a lens position determining unit that determines a focus lens position to be set as a start point of the AF search by the focal adjustment unit based upon the approximate distance to the face having been determined by the distance calculation unit.

Claims

1. A digital camera comprising:

an image-capturing unit that receives light transmitted through a photographic optical system and outputs image signals;

a lens drive unit that moves a focus lens constituting the photographic optical system along an optical axis;

an evaluation value calculation unit that calculates a focal point evaluation value that changes in correspondence to a position assumed by the focus lens based upon the image signals;

a focal adjustment unit that executes an AF search by repeatedly engaging the image-capturing unit and the evaluation value calculation unit in operation as the focus lens is made to move along the optical axis by the lens drive unit, detecting a focus match position based upon resulting focal point evaluation values and driving the focus lens to the focus match position;

a face recognition unit that recognizes a face of a person in an image by analyzing the image signals;

a distance calculation unit that determines an approximate distance to the face based upon the size of the recognized face; and

a lens position determining unit that determines a focus lens position to be set as a start point of the AF search by the focal adjustment unit based upon the approximate distance to the face having been determined by the distance calculation unit.

2. A digital camera according to claim 1, wherein:

the lens position determining unit determines the focus lens position to be set as the start point of the AF search based upon the distance having been determined by the distance calculation unit and a zoom condition of the photographic optical system.

3. A digital camera according to claim 1, wherein:

the lens position determining unit determines the focus lens position to be set as the start point so that a range over which the lens moves during the AF search increases when the size of the recognized face is smaller.

4. A digital camera according to claim 1, wherein:

the lens position determining unit selects a face with a largest size if a plurality of faces are recognized in a single image by the face recognition unit and determines the focus lens position to be set as the start point based upon the approximate distance corresponding to the largest size face.

5. A digital camera according to claim 1, wherein:

the lens position determining unit also determines a focus lens position to be set as an end point of the AF search.

6. A digital camera according to claim 1, wherein:

the distance calculation unit includes a table correlating the face size with the approximate distance to the face and ascertains the approximate distance to the face by referencing the table.

7. A digital camera according to claim 1, wherein:

the start point of the AF search determined by the lens position determining unit corresponds to a position offset from a position corresponding to an actual distance to the face that is estimated by a predetermined extent along a direction opposite from a direction of the AF search.

8. A digital camera according to claim 1, wherein:

the evaluation value calculation unit calculates the focal point evaluation value by designating an area corresponding to the face of the person recognized by the face recognition unit as an AF area.

9. A digital camera according to claim 1, wherein:

the evaluation value calculation unit splits a photographic image plane into a predetermined plurality of areas and calculates the focal point evaluation value by designating an area among the plurality of areas that contain the face of the person recognized by the face recognition unit as a selected AF area.

10. A digital camera according to claim 1, wherein:

the focal adjustment unit starts the AF search by adopting a so-called hill-climbing method from the AF search start point determined by the lens position determining unit.

11. A digital camera according to claim 1, wherein:

the focal adjustment unit starts and AF search scan by adopting a scanning method from the AF search start point determined by the lens position determining unit.

12. A digital camera according to claim 11, wherein:

the focal adjustment unit scans over a predetermined distance range from the AF search start point determined by the lens position determining unit.

13. A digital camera according to claim 1, wherein:

the lens position determining unit sets the AF search start point further toward an infinity side when the size of the recognized face is smaller.