Exposure control method, exposure control apparatus and image pickup apparatus

• US 8,031,237 B2
• Filed: 08/24/2006
• Issued: 10/04/2011
• Est. Priority Date: 08/26/2005
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Kirisawa, Tsukasa
• Primary Examiner(s): Henn; Timothy J
• Application Number:
  US11/466,981
• Publication Number:
  US 20070046789A1
• Time in Patent Office: 1,867 Days
• Field of Search: 3482261-2281
• US Class Current: 348/228.1
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/73 by influencing the exposure time
• CPC Class Codes: H04N 23/745 Detection of flicker frequency or suppression of flicker wherein the flicker is caused by illumination, e.g. due to fluorescent tube illumination or pulsed LED illumination

Abstract

A technique of acquiring a width obtaining an appropriate exposure with minimum restrictions, while accurately correcting flickering is provided. An exposure control method includes integrating a video signal obtained by shooting a subject by means of a CMOS imaging element as input video signal over not less than a horizontal period, normalizing the integral value or the difference value of the integral value between neighboring fields or frames, extracting the integral value or the difference value after the normalization as flicker spectrum, determining, based on the extracted flicker spectrum, the presence or absence of a flicker component contained in the video signal obtained by the imaging element and controlling the exposure value, using a program diagram for preferentially employing the shutter speed less liable to produce flickering when it is determined that the video signal contains a flicker component.

Claims

1. An exposure control method of an image pickup apparatus having an XY address scanning type imaging element, the method comprising:

(a) obtaining a video signal by shooting a subject by means of the imaging element;

(b) determining a phase of a flicker showing cyclicity in the video signal using a power supply frequency;

(c) integrating the video signal as input video signal over not less than a horizontal period;

(d) normalizing an integral value obtained in the integrating step or the difference value between integral values of adjacent fields or frames;

(e) extracting a flicker spectrum from the normalized integral value or the normalized difference value;

f) determining, based on the extracted flicker spectrum, the presence or absence of a flicker component contained in the video signal obtained by the imaging element;

(g) determining whether a current environment includes lighting of a flickering light source; and

(h) in response to a determination that the current environment includes lighting of the flickering light source, controlling an exposure value by setting a program diagram adapted to use a shutter speed of n/100 seconds for 60 fps, n/120 seconds for 50 fps and n/100 seconds for 30 fps, wherein the program diagram is maintained so long as an appropriate exposure can be realized.

2. The method according to claim 1, wherein the phase of the flicker of an arbitrarily selected line in an image plane of the video signal is computed from a flicker spectrum obtained one frame before and a flicker spectrum currently obtained and the presence of flickering is determined if the flicker component is produced with a phase difference due to a relation between field or frame frequency of a broadcasting system and a power supply frequency.

3. The method according to claim 1, wherein a program diagram adapted to preferentially use a shutter speed of n/120 seconds for 60 fps, n/100 seconds for 50 fps and n/120 seconds for 30 fps, where n is a positive integer, is initially set according to the frame rate of the image pickup apparatus so long as an appropriate exposure can be realized.

4. An exposure control apparatus of an image pickup apparatus having an XY address scanning type imaging element, the apparatus comprising:

a video signal obtaining unit configured to obtain a video signal by shooting a subject by means of the imaging element;

flicker determining means for;

(a) determining a phase of a flicker showing cyclicity in the video signal using a power supply frequency;

(b) integrating a video signal obtained by shooting a subject by means of the imaging element as input video signal over not less than a horizontal period;

(c) normalizing an integral value obtained by integrating the video or the difference value between integral values of adjacent fields or frames;

(d) extracting flicker spectrum from the normalized integral value or the normalized difference value, and determining, based on the extracted flicker spectrum, the presence or absence of a flicker component contained in the video signal obtained by the imaging element; and

exposure value controlling means for, in response to a determination that a current environment includes lighting of a flickering light source, controlling an exposure value by setting a program diagram adapted to use a shutter speed of n/100 seconds for 60 fps, n/120 seconds for 50 fps and n/100 seconds for 30 fps, wherein the program diagram is maintained so long as an appropriate exposure can be realized.

5. The apparatus according to claim 4, wherein the flicker determining means computes the phase of the flicker of an arbitrarily selected line in an image plane of the video signal from a flicker spectrum obtained one frame before and a flicker spectrum currently obtained and determines the presence of flickering if the flicker component is produced with a phase difference due to a relation between field or frame frequency of a broadcasting system and a power supply frequency.

6. The apparatus according to claim 4, wherein the exposure value controlling means initially sets a program diagram adapted to preferentially use a shutter speed of n/120 seconds for 60 fps, n/100 seconds for 50 fps and n/120 seconds for 30 fps, where n is a positive integer, according to the frame rate of the image pickup apparatus so long as an appropriate exposure can be realized.

7. An image pickup apparatus comprising:

an XY address scanning type imaging element;

a video signal obtaining unit configured to obtain a video signal by shooting a subject by means of the imaging element;

flicker determining means for;

(a) determining a phase of a flicker showing cyclicity in the video signal using a power supply frequency;

(b) integrating a video signal obtained by shooting a subject by means of the imaging element as input video signal over not less than a horizontal period;

(c) normalizing an integral value obtained by integrating the video or the difference value between integral values of adjacent fields or frames;

(d) extracting flicker spectrum from the normalized integral value or the normalized difference value; and

(e) determining, based on the extracted flicker spectrum, the presence or absence of a flicker component contained in the video signal obtained by the imaging element from the extracted flicker spectrum; and

exposure value controlling means for, in response to a determination that a current environment includes lighting of a flickering light source, controlling an exposure value by setting a program diagram adapted to use a shutter speed of n/100 seconds for 60 fps, n/120 seconds for 50 fps and n/100 seconds for 30 fps, wherein the program diagram is maintained so long as an appropriate exposure can be realized.

8. The apparatus according to claim 7, wherein the flicker determining means computes the phase of the flicker of an arbitrarily selected line in an image plane of the video signal from a flicker spectrum obtained one frame before and a flicker spectrum currently obtained and determines the presence of flickering if the flicker component is produced with a phase difference due to a relation between field or frame frequency of a broadcasting system and a power supply frequency.

9. The apparatus according to claim 7, wherein the exposure value controlling means initially sets a program diagram adapted to preferentially use a shutter speed of n/120 seconds for 60 fps, n/100 seconds for 50 fps and n/120 seconds for 30 fps, where n is a positive integer, according to the frame rate of the video signal to be transmitted so long as an appropriate exposure can be realized.

10. The apparatus according to claim 7, further comprising:

arithmetic operation means for estimating the flicker component from the flicker spectrum extracted by the flicker determining means and performing an arithmetic operation on the estimated flicker component and the input video signal so as to cancel the estimated flicker component when the flicker determining means determines that the video signal contains any flicker component and the exposure value controlling means is not able to set the shutter speed so as to produce a flicker-free state for the purpose of realizing an appropriate exposure.

11. An exposure control apparatus of an image pickup apparatus having an XY address scanning type imaging element, the apparatus comprising:

a video signal obtaining unit configured to obtain a video signal by shooting a subject by means of the imaging element;

a flicker determining unit configured to;

(a) determine a phase of a flicker showing cyclicity in the video signal using a power supply frequency;

(b) integrate a video signal obtained by shooting a subject by means of the imaging element as input video signal over not less than a horizontal period;

(c) normalize an integral value obtained by integrating the video or the difference value between integral values of adjacent fields or frames;

(d) extract flicker spectrum from the normalized integral value or the normalized difference value; and

(e) determine, based on the extracted flicker spectrum, the presence or absence of a flicker component contained in the video signal obtained by the imaging element from the extracted flicker spectrum; and

an exposure value controlling unit configure to, in response to a determination that a current environment includes lighting of a flickering light source, control an exposure value by setting a program diagram adapted to use a shutter speed of n/100 seconds for 60 fps, n/120 seconds for 50 fps and n/100 seconds for 30 fps, wherein the program diagram is maintained so long as an appropriate exposure can be realized.

12. An image pickup apparatus comprising:

an XY address scanning type imaging element;

a video signal obtaining unit configured to obtain a video signal by shooting a subject by means of the imaging element;

a flicker determining unit that;

(a) determines a phase of a flicker showing cyclicity in the video signal using a power supply frequency;

(b) integrates a video signal obtained by shooting a subject by means of the imaging element as input video signal over not less than a horizontal period;

(c) normalizes an integral value obtained by integrating the video or the difference value between integral values of the adjacent fields or frames;

(d) extracts flicker spectrum from the normalized integral value or the normalized difference value; and

(e) determines, based on the extracted flicker spectrum, the presence or absence of a flicker component contained in the video signal obtained by the imaging element from the extracted flicker spectrum; and

an exposure value controlling unit configure to, in response to a determination that a current environment includes lighting of a flickering light source, control an exposure value by setting a program diagram adapted to use a shutter speed of n/100 seconds for 60 fps, n/120 seconds for 50 fps and n/100 seconds for 30 fps, wherein the program diagram is maintained so long as an appropriate exposure can be realized.