Image capturing apparatus and control method controlling exposure time of image sensor

• US 8,736,748 B2
• Filed: 02/06/2012
• Issued: 05/27/2014
• Est. Priority Date: 02/21/2011
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Takita, Taro
• Primary Examiner(s): Haskins, Twyler
• Assistant Examiner(s): Haliyur, Padma
• Application Number:
  US13/366,504
• Publication Number:
  US 20120212663A1
• Time in Patent Office: 841 Days
• Field of Search: 348/221.1, 348/222.1, 348/229.1, 348/234, 348/235, 348/362, 348/363, 348/364, 348/366
• US Class Current: 348/362
• CPC Class Codes: H04N 23/73 by influencing the exposure time
• CPC Class Codes: H04N 23/75 by influencing optical camera components

Abstract

There is provided an image capturing apparatus, comprising an image capturing unit configured to acquire video data at a first frame rate or a second frame rate higher than the first frame rate; and a control unit configured to perform control of an aperture and an exposure time within a range in which the exposure time is shorter than or equal to a maximum exposure time that is a reciprocal of a frame rate of the image capturing unit, so that luminance of the image signal acquired by the image capturing unit is at a predetermined level, wherein when the image capturing unit is operating at the first frame rate, the control unit performs the control within a range in which the exposure time is shorter than a first time that is a reciprocal of the first frame rate.

Claims

1. An image capturing apparatus, comprising:

an optical system including an aperture;

a first driving unit configured to drive the optical system;

an image sensor configured to generate an image signal by photoelectric conversion of light incident from the optical system;

a second driving unit configured to drive the image sensor;

a detecting unit configured to detect a luminance level of the image signal;

a first setting unit configured to set a first mode in which motion images are not recorded or a second mode in which motion images are recorded; and

a control unit configured to control the second driving unit to read out an image signal from the image sensor at a first frame rate in a case where the first setting unit sets the first mode or at a second frame rate higher than the first frame rate in a case where the first setting unit sets the second mode,

wherein, in a case where the first setting unit sets the first mode, the control unit controls the second driving unit to drive the image sensor so that an exposure time of the image sensor is shorter than or equal to a time corresponding to a reciprocal of the second frame rate, and controls the first driving unit to drive the aperture so that the luminance level detected by the detecting unit is at a predetermined level.

2. The image capturing apparatus according to claim 1, further comprising:

a second setting unit configured to set switching of the frame rate from the first frame rate to the second frame rate to “

enabled”

or “

disabled”

,

wherein in a case where the switching is set “

enabled”

, the control unit performs the control within a range in which the exposure time is shorter than a time corresponding to a reciprocal of the first frame rate.

3. The image capturing apparatus according to claim 1, further comprising:

an amplification unit configured to amplify the image signal,

wherein in a case where the second driving unit drives the image sensor at the first frame rate,

if the luminance level of the image signal is lower than the predetermined level in a state in which the exposure time is shorter than or equal to the time corresponding to the reciprocal of the second frame rate even though the aperture is opened to a maximum, the control unit performs the control within a range in which the exposure time is shorter than or equal to a time corresponding to a reciprocal of the first frame rate, and

in a case where the frame rate is switched to the second frame rate, the control unit changes the exposure time to the time corresponding to the reciprocal of the second frame rate and controls the amplification unit to amplify the image signal so as to compensate for a drop in luminance level that accompanies the change in the exposure time.

4. The image capturing apparatus according to claim 1, further comprising:

a frame-cyclic noise reduction unit configured to reduce noise in the image signal,

wherein in a case where the second driving unit drives the image sensor at the second frame rate, the noise reduction unit reduces noise using a cyclic coefficient higher than a cyclic coefficient for a case of the first frame rate.

5. The image capturing apparatus according to claim 1, further comprising:

a reception unit configured to receive a switching instruction to switch the frame rate from the first frame rate to the second frame rate,

wherein in a case where the switching instruction is received in a case where the exposure time is longer than a maximum exposure time corresponding to the second frame rate, the control unit controls the first driving unit to open the aperture so as to compensate for a drop in the luminance of the image signal as a result of shortening the exposure time to the maximum exposure time corresponding to the second frame rate, and also performs control for switching the frame rate from the first frame rate to the second frame rate, and

in the switching control, the control unit gradually changes the frame rate from the first frame rate to the second frame rate while the aperture is being gradually opened by the first driving unit.

6. The image capturing apparatus according to claim 5, wherein, in the switching control, the control unit changes the frame rate promptly to a frame rate at which an exposure time at a time of reception of the switching instruction is a maximum exposure time, and then gradually to the second frame rate.

7. The image capturing apparatus according to claim 5, further comprising:

a motion detection unit configured to detect a motion of a subject included in the image signal,

wherein, in the switching control, if a degree of the detected motion is larger than a predetermined degree, the control unit promptly changes the frame rate from the first frame rate to the second frame rate, and amplifies the image signal so as to compensate for a drop in luminance level that accompanies the change in the frame rate.

8. The image capturing apparatus according to claim 7, wherein after the amplification has been started and while the aperture is being gradually opened by the first driving unit, the control unit gradually reduces a degree of the amplification of the amplification unit in accordance with an increase in the luminance of the image signal that accompanies the opening of the aperture.

9. The image capturing apparatus according to claim 5, wherein in the switching control, if the frame rate does not reach the second frame rate even after the aperture has been opened to a maximum, the control unit promptly changes the frame rate to the second frame rate and amplifies the image signal so as to compensate for a drop in luminance level that accompanies the change in the frame rate.

10. A control method for an image capturing apparatus comprising an optical system including an aperture, a first driving unit configured to drive the optical system, an image sensor configured to generate an image signal by photoelectric conversion of light incident from the optical system, and a second driving unit configured to drive the image sensor, the control method comprising:

a detecting step of detecting a luminance level of the image signal;

a first setting step of setting a first mode in which motion images are not recorded or a second mode in which motion images are recorded; and

a control step of controlling the second driving unit to read out an image signal from the image sensor at a first frame rate in a case where the first setting step sets the first mode or at a second frame rate higher than the first frame rate in a case where the first setting step sets the second mode,

wherein, in a case where the first frame rate the first setting step sets the first mode, the control step controls the second driving unit to drive the image sensor so that an exposure time of the image sensor is shorter than or equal to a time corresponding to a reciprocal of the second frame rate, and controls the first driving unit to drive the aperture so that the luminance level detected in the detecting step is at a predetermined level.

11. The control method according to claim 10, further comprising:

a reception step of receiving a switching instruction to switch the frame rate from the first frame rate to the second frame rate,

wherein in a case where the switching instruction is received in a case where the exposure time is longer than a maximum exposure time corresponding to the second frame rate, in the control step, the first driving unit is controlled to open the aperture so as to compensate for a drop in the luminance of the image signal as a result of shortening the exposure time to the maximum exposure time corresponding to the second frame rate, and control is also performed for switching the frame rate from the first frame rate to the second frame rate, and

in the switching control, the frame rate is gradually changed from the first frame rate to the second frame rate while the aperture is being gradually opened by the first driving unit.

12. A non-transitory computer-readable storage medium that stores a program for causing a computer to execute the method according to claim 10.