Video camera apparatus and automatic focusing circuit

• US 5,638,122 A
• Filed: 05/09/1996
• Issued: 06/10/1997
• Est. Priority Date: 06/24/1993
• Status: Expired due to Term

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Kawaguchi, Naoki, Torii, Reiko
• Primary Examiner(s): Garber, Wendy
• Assistant Examiner(s): CHRISTENSEN, ANDREW BRUCE
• Application Number:
  US08/651,853
• Time in Patent Office: 397 Days
• Field of Search: 348/345, 348/349, 348/354, 348/355, 250/201.7, 250/201.8
• US Class Current: 348/349
• CPC Class Codes: H04N 23/673 based on contrast or high frequency components of image signals, e.g. hill climbing method

Abstract

An automatic focusing circuit comprises: a lens section including a focusing lens; photoelectric converting means for photoelectrically converting an amount of light which passed through the lens section; a first filter having first frequency characteristics to extract a first high frequency component from a luminance signal; a second filter which is used to extract a second high frequency component from said luminance signal and which has frequency characteristics steeper than those of the first filter; optical black level detecting means for detecting an optical black level of an image pickup signal; and a control section to control the focusing lens on the basis of the optical black level and the first and second high frequency components.

Claims

1. An automatic focusing circuit including a lens section having a movable focusing lens driven at a controllable speed and photoelectric converting means for photoelectrically converting an amount of light passing through said lens section into an image pickup signal, comprising:

first filter means having first frequency characteristics for extracting a first high frequency component from a luminance signal included in said image pickup signal;

second filter means having second frequency characteristics steeper than said first frequency characteristics for extracting a second high frequency component from said luminance signal;

optical black level detecting means for detecting an optical black level of said image pickup signal; and

control means for controlling the speed of moving said focusing lens on the basis of said optical black level and said first and second high frequency component such that said focusing lens is moved at a high speed when said first high frequency component is less than a predetermined threshold which is a function of said optical black level, said focusing lens is moved at a low speed when (i) said first high frequency component is larger than said predetermined threshold and (ii) a ratio of said second high frequency component to said first high frequency component is substantially equal to a predetermined value, and said focusing lens is moved at an intermediate speed when (i) said first high frequency component is larger than said predetermined threshold and (ii) said ratio of said second high frequency component to said first high frequency component is not substantially equal to said predetermined value.

2. A circuit according to claim 1, wherein said predetermined threshold has a value which is twice said optical black level.

3. A circuit according to claim 1, where said predetermined value is equal to 1.

4. A video camera having a focusing function, comprising:

a lens section having a movable focusing lens driven at a controllable speed;

photoelectric converting means for photoelectrically converting an amount of light passing through said lens section into an image pickup signal;

first filter means having first frequency characteristics for extracting a first high frequency component from a luminance signal included in said image pickup signal;

second filter means having second frequency characteristics steeper than said first frequency characteristics for extracting a second high frequency component from said luminance signal;

optical black level detecting means for detecting an optical black level of an image pickup signal; and

control means for controlling the speed of moving said focusing lens on the basis of said optical black level and said first and second high frequency component such that said focusing lens is moved at a high speed when said first high frequency component is less than a predetermined threshold which is a function of said optical black level, said focusing lens is moved at a low speed when (i) said first high frequency component is larger than said predetermined threshold and (ii) a ratio of said second high frequency component to said first high frequency component is substantially equal to a predetermined value, and said focusing lens is moved at an intermediate speed when (i) said first high frequency component is larger than said predetermined threshold and (ii) said ratio of said second high frequency component to said first high frequency component is not substantially equal to said predetermined value.

5. A video camera according to claim 4, wherein said predetermined threshold has a value which is twice said optical black level.

6. A video camera according to claim 4, wherein said predetermined value is equal to 1.

7. An automatic focus control method for use with a lens section having a movable focusing lens driven at a controllable speed and photoelectric converting means for photoelectrically converting an amount of light passing through said lens section into an image pickup signal, comprising the steps of:

extracting a first high frequency component from a luminance signal included in said image pickup signal using first filter means having first frequency characteristics;

extracting a second high frequency component from said luminance signal having second frequency characteristics steeper than said first frequency characteristics;

detecting an optical black level of said image pickup signal; and

controlling the speed of moving said focusing lens on the basis of said optical black level and said first and second high frequency components such that said focusing lens is moved at a high speed when said first high frequency component is less than a predetermined threshold which is a function of said optical black level, said focusing lens is moved at a low speed when (i) said first high frequency component is larger than said predetermined threshold and (ii) a ratio of said second high frequency component to said first high frequency component is substantially equal to a predetermined value, and said focusing lens is moved at an intermediate speed when (i) said first high frequency component is larger than said predetermined threshold and (ii) said ratio of said second high frequency component to said first high frequency component is not substantially equal to said predetermined value.

8. A method according to claim 7, wherein said predetermined threshold has a value which is twice said optical black level.

9. A method according to claim 7, wherein said predetermined value is equal to 1.

10. An automatic focusing circuit including a lens section having a movable focusing lens driven at a controllable speed and photoelectric converting means for photoelectrically converting an amount of light passing through said lens section into an image pickup signal, comprising:

filter means having frequency characteristics for extracting a high frequency component from a luminance signal included in said image pickup signal;

optical black level detecting means for detecting an optical black level of said image pickup signal; and

control means for controlling the speed of moving said focusing lens on the basis of a comparison of said optical black level and said high frequency component.

11. A video camera having a focusing function, comprising:

a lens section having a movable focusing lens driven at a controllable speed;

photoelectric converting means for photoelectrically converting an amount of light passing through said lens section into an image pickup signal;

filter means having frequency characteristics for extracting a high frequency component from a luminance signal included in said image pickup signal;

optical black level detecting means for detecting an optical black level of an image pickup signal; and

control means for controlling the speed of moving said focusing lens on the basis of a comparison of said optical black level and said high frequency component.

12. An automatic focus control method for use with a lens section having a movable focusing lens driven at a controllable speed and photoelectric converting means for photoelectrically converting an amount of light passing through said lens section into an image pickup signal, comprising the steps of:

extracting a high frequency component from a luminance signal included in said image pickup signal using filter means having frequency characteristics;

detecting an optical black level of said image pickup signal; and

controlling the speed of moving said focusing lens on the basis of a comparison of said optical black level and said high frequency component.