Auto-focus apparatus, image-capture apparatus, and auto-focus method

• US 20080002960A1
• Filed: 06/28/2007
• Published: 01/03/2008
• Est. Priority Date: 06/30/2006
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Ito, Yujiro, Suto, Hidekazu
• Granted Patent: US 7,620,311 B2
• Time in Patent Office: Days
• US Class Current: 396/125
• CPC Class Codes: G03B 13/36 Autofocus systems
• 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

Disclosed is an auto-focus apparatus including an evaluation value calculator periodically calculating evaluation values using high frequency components of image signals in a specific region of a subject image, a distance measurement unit measuring a distance to a subject and output a distance measurement result, a control unit outputting instruction values based on the evaluation values and determines whether a subject image is in-focus or out-of-focus, and a storage storing the distance measurement results and lens positions. In the apparatus, after searching the peak of the evaluation values, the control unit returns the lens to the position at which the relative maximum has been detected, obtains evaluation values, stores lens positions and distance measurement results when the evaluation values satisfy a prescribed condition, and retrieves distance measurement results and lens positions when the number of times that results are stored reaches a prescribed number, and computes a correction amount.

Claims

1. An auto-focus apparatus comprising:

an evaluation value calculator configured to periodically calculate evaluation values using high frequency components of image signals in a specific region of a subject image captured by an image-capture unit;

a distance measurement unit configured to measure a distance to a subject and output a distance measurement result;

a control unit configured to output instruction values provided to a lens driver for driving a focus lens based on the evaluation values and determines whether a subject image is in-focus or out-of-focus, using the evaluation values; and

a storage configured to store distance measurement results and positions of the focus lens, wherein

after the control unit operates to search the peak of the evaluation values while moving positions of the focus lens and detects the relative maximum of the evaluation values, the control unit returns the focus lens to the position corresponding to a point at which the relative maximum has been detected, obtains the evaluation values calculated by the evaluation value calculator, stores the focus position and distance measurement results when the evaluation values satisfy a prescribed condition, and retrieves the distance measurement results and focus positions when the number of times that the focus positions and distance measurement results are stored reaches a prescribed number, and computes a correction amount for distance measurement results output from the distance measurement unit based on a relation between the retrieved distance measurement results and focus positions.

2. An auto-focus apparatus according to claim 1, wherein

the prescribed condition involves that when a first evaluation value is defined as the relative maximum of the evaluation values and a second evaluation value is defined as the evaluation value obtained when the focus lens returns to the position corresponding to a point at which the relative maximum has been detected, a value obtained from dividing the second evaluation value by the first evaluation value is larger than a prescribed threshold.

3. An auto-focus apparatus according to claim 1, wherein

the prescribed condition involves that when a first evaluation value is defined as the relative maximum of the evaluation values and a second evaluation value is defined as the evaluation value obtained when the focus lens returns to the position corresponding to a point at which the relative maximum has been detected, a value obtained from dividing the second evaluation value by the first evaluation value is larger than the first threshold and the second evaluation value is larger than the second threshold.

4. An auto-focus apparatus according to claim 1, wherein

a luminance addition value calculator configured to calculate luminance addition values by integrating luminance of the image signals in the specific region, wherein

when a first luminance addition value is defined as the luminance addition value obtained when the relative maximum has been detected, and a second luminance addition value is defined as the luminance addition value obtained a prescribed fields before the current field at which the relative maximum has been detected, the control unit stores the distance measurement result and the focus position obtained at a point where the control unit determines that a value obtained from dividing the second luminance addition value by the first luminance value falls within a prescribed threshold and the evaluation values satisfy the prescribed condition.

5. An auto-focus apparatus according to claim 1, further comprising

a wobbling detector configured to detect wobbling applied to the auto-focus apparatus, wherein

the control unit stores the distance measurement result and the focus position obtained at a point where the control unit determines that the magnitude detected by the wobbling detector at a point where the relative maximum of the evaluation values has been detected falls within a prescribed range of values, and the evaluation values satisfy the prescribed condition.

6. An auto-focus apparatus according to claim 5, wherein

the wobbling detector indicates an angular velocity sensor or an acceleration sensor.

7. An auto-focus apparatus comprising:

an evaluation value calculator configured to periodically calculate evaluation values using high frequency components of image signals in a specific region of a subject image captured by an image-capture unit;

a distance measurement unit configured to measure a distance to a subject and output a distance measurement result;

a control unit configured to output instruction values provided to a lens driver for driving a focus lens based on the evaluation values and determines whether a subject image is in-focus or out-of-focus, using the evaluation value; and

a storage configured to store distance measurement results and positions of the focus lens, wherein

if after the control unit operates to search the peak of the evaluation values while moving positions of the focus lens and detects the relative maximum of the evaluation values, the control unit returns the focus lens to the position corresponding to a point at which the relative maximum has been detected, obtains the evaluation values calculated by the evaluation value calculator, stores the focus position and distance measurement results when the evaluation values satisfy a prescribed condition, and detects enabling signals transmitted from the control unit, the control unit retrieves the distance measurement results and focus positions when the number of times that the focus positions and distance measurement results are stored reaches a prescribed number, and computes a correction amount for distance measurement results output from the distance measurement unit based on a relation between the retrieved distance measurement results and focus positions.

8. An auto-focus apparatus according to claim 7, wherein

the control unit stores distance measurement results and positions of the focus lens at the position at which the enabling signals have been detected, retrieves the distance measurement results and focus positions, and computes a correction amount for distance measurement results output from the distance measurement unit based on a relation between the retrieved distance measurement results and focus positions.

9. An image-capture apparatus comprising:

an auto-focus apparatus including an image-capture unit configured to image a subject, an evaluation value calculator configured to periodically calculate evaluation values using high frequency components of image signals in a specific region of a subject image captured by the image capture unit, a distance measurement unit configured to measure a distance to the subject and output a distance measurement result, a control unit configured to output instruction values provided to a lens driver for driving a focus lens based on the evaluation values and determines whether a subject image is in-focus or out-of-focus, using the evaluation values, and a storage configured to store distance measurement results and positions of the focus lens, wherein

after the control unit operates to search the peak of the evaluation values while moving positions of the focus lens and detects the relative maximum of the evaluation values, the control unit returns the focus lens to the position corresponding to a point at which the relative maximum has been detected, obtains the evaluation values calculated by the evaluation value calculator, stores the focus position and distance measurement results when the evaluation values satisfy a prescribed condition, and retrieves the distance measurement results and focus positions when the number of times that the focus positions and distance measurement results are stored reaches a prescribed number, and computes a correction amount for distance measurement results output from the distance measurement unit based on a relation between the retrieved distance measurement results and focus positions.

10. An image-capture apparatus comprising:

an auto-focus apparatus including an operation unit, an image-capture unit configured to image a subject, an evaluation value calculator configured to periodically calculate evaluation values using high frequency components of image signals in a specific region of a subject image captured by the image capture unit, a distance measurement unit configured to measure a distance to the subject and output a distance measurement result, a control unit configured to output instruction values provided to a lens driver for driving a focus lens based on the evaluation values and determines whether a subject image is in-focus or out-of-focus, using the evaluation values, and a storage configured to store distance measurement results and positions of the focus lens, wherein

if after the control unit operates to search the peak of the evaluation values while moving positions of the focus lens and detects the relative maximum of the evaluation values, the control unit returns the focus lens to the position corresponding to a point at which the relative maximum has been detected, obtains the evaluation values calculated by the evaluation value calculator, stores the focus position and distance measurement result when the evaluation values satisfy a prescribed condition, and detects enabling signals transmitted from the control unit, the control unit retrieves the distance measurement results and focus positions when the number of times that the focus position and distance measurement result are stored reaches a prescribed number, and computes a correction amount for distance measurement results output from the distance measurement unit based on a relation between the retrieved distance measurement results and focus positions.

11. An auto-focus method performed by an auto-focus apparatus configured to automatically adjust focus o a subject using distance information to the subject and evaluation values obtained in image processing, comprising the steps of:

periodically calculating evaluation values using high frequency components of image signals in a specific region of a subject image captured by an image capture unit,

measuring a distance to a subject and outputting a distance measurement result,

operating to search the peak of the evaluation values based on the evaluation values and distance measurement result while moving positions of a focus lens,

calculating the evaluation values by returning the focus lens to the position corresponding to a point at which the relative maximum has been detected after having detected the relative maximum of the evaluation values,

storing the distance measurement results and focus positions in the storage when the evaluation values satisfy a prescribed condition, and

retrieving the distance measurement results and focus positions when the number of times that the focus positions and distance measurement results are stored reaches a prescribed number, and

computing a correction amount for distance measurement results output from the distance measurement unit based on a relation between the retrieved distance measurement results and focus positions.

12. An auto-focus method performed by an auto-focus apparatus configured to automatically adjust focus on a subject using distance information to the subject and evaluation values obtained in image processing, comprising the steps of:

periodically calculating evaluation values using high frequency components of image signals in a specific region of a subject image captured by an image capture unit,

measuring a distance to a subject and outputting a distance measurement result,

operating to search the peak of the evaluation values based on the evaluation values and distance measurement result while moving positions of a focus lens,

calculating the evaluation values by returning the focus lens to the position corresponding to a point at which the relative maximum has been detected after having detected the relative maximum of the evaluation values,

storing the distance measurement results and focus positions in the storage when the evaluation values satisfy a prescribed condition if enabling signals transmitted from the control unit are detected,

retrieving the distance measurement results and focus positions when the number of times that the focus positions and distance measurement results are stored reaches a prescribed number, and

computing a correction amount for distance measurement results output from the distance measurement unit based on a relation between the retrieved distance measurement results and focus positions.

13. An auto-focus apparatus comprising:

an evaluation value calculator configured to periodically calculate evaluation values using high frequency components of image signals in a specific region of a subject image captured by an image capture unit;

a distance measurement unit configured to measure a distance to a subject and output a distance measurement result;

a control unit configured to output instruction values provided to a lens driver for driving a focus lens based on the evaluation values and determine whether a subject image is in-focus or out-of-focus, using the evaluation values, and

a storage configured to store distance measurement results and positions of the focus lens, wherein

after the control unit operates to search the peak of the evaluation values while moving positions of the focus lens and detects the relative maximum of the evaluation values, the control unit returns the focus lens to the position corresponding to a point at which the relative maximum has been detected, obtains the evaluation values calculated by the evaluation value calculator, stores the focus positions, distance measurement results and determination results as to whether or not the evaluation values satisfy a prescribed condition, and retrieves the distance measurement results, focus positions and determination results when the number of times the distance measurement results, focus positions and determination results are stored reaches a prescribed number, and computes a correction amount for distance measurement results output from the distance measurement unit based on a relation between the retrieved distance measurement results, focus positions and determination results.