Electronic camera using flash for exposure control

• US 6,359,651 B1
• Filed: 10/05/1999
• Issued: 03/19/2002
• Est. Priority Date: 10/06/1998
• Status: Expired due to Term

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Yokonuma, Norikazu
• Primary Examiner(s): Garber, Wendy R.
• Assistant Examiner(s): Tillery, Rashawn N
• Application Number:
  US09/412,651
• Time in Patent Office: 896 Days
• Field of Search: 348/370, 348/371, 348/65, 348/68, 348/69, 348/222, 348/225, 348/362-366, 348/229, 348/296, 396/166, 396/155-169, 396/106, 600/160, 600/180, 382/162, 382/167, 358/518
• US Class Current: 348/370
• CPC Class Codes: H04N 2101/00 Still video cameras
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means

Abstract

A camera CPU internally provided at a digital still camera determines an exposure time based upon an image signal input from a CCD via a control circuit. The camera CPU also implements preliminary photographing which is accompanied by light emission by an electronic flash unit, obtains a light emission quantity at the electronic flash unit for main photographing based upon the results of preliminary photographing and determines the flash time using the light emission quantity. If the flash time is longer than the exposure time, the camera CPU reduces the length of flash time. The camera CPU calculates the quantity of underexposure occurring as a result of the exposure ending before the illumination by the electronic flash unit is completed. An image processing circuit engages in color correction by incorporating the quantity of underexposure that has been calculated in advance when it processes image data obtained through an imaging operation.

Claims

1. An electronic camera comprising:

an imaging device that performs photoelectric conversion on an image formed by a taking lens and outputs an image signal;

an exposure time determination unit that determines an exposure time for said imaging device based upon a subject brightness;

a light emission quantity control unit that, when performing photographing with an electronic flash unit, controls a light emission quantity by controlling a length of flash time at said electronic flash unit;

an arithmetic operation unit that calculates a quantity of underexposure occurring as a result of an interrupted exposure of a subject illuminated by said electronic flash unit due to a shorter exposure time when the flash time is longer than the exposure time; and

a signal processing unit that performs image processing on image data generated by amplifying said image signal output by said imaging device at a specific gain by incorporating the quantity of underexposure calculated at said arithmetic operation unit when engaging in, at least, either adjustment of said gain or color correction for said image processing.

2. An electronic camera according to claim 1, further comprising:

a data table in which processing parameters corresponding to said quantity of underexposure are stored, wherein;

said signal processing unit performs said image processing using said processing parameters read out in correspondence to said quantity of underexposure from said data table.

3. An electronic camera according to claim 1, wherein:

said signal processing unit separates an image of a background from an image of a main subject and performs color correction individually for the background and the main subject.

4. An electronic camera comprising:

an imaging device that performs photoelectric conversion on an image formed by a taking lens and outputs an image signal;

an exposure time determination unit that determines an exposure time for said imaging device based upon a subject brightness;

a light emission quantity control unit that, when performing photographing with an electronic flash unit, controls a light emission quantity by controlling a length of flash time at said electronic flash unit; and

an exposure quantity control unit that ensures that a flash operation by said electronic flash unit is completed within said exposure time by reducing said flash time if said flash time is longer than said exposure time.

5. An electronic camera according to claim 4, further comprising:

a signal processing unit that performs image processing on image data generated by amplifying said image signal output by said imaging device at a specific gain; and

an arithmetic operation unit that calculates a quantity of underexposure occurring due to a reduction in said flash time effected by said light emission quantity control unit, wherein;

said signal processing unit engages in, at least, either adjustment of said gain or color correction through said image processing based upon said quantity of underexposure calculated at said arithmetic operation unit.

6. An electronic camera according to claim 5, further comprising:

a data table in which processing parameters corresponding to said quantity of underexposure are stored, wherein;

said signal processing unit performs said image processing using said processing parameters read out in correspondence to said quantity of underexposure from said data table.

7. An electronic camera according to claim 5, wherein:

said signal processing unit separates an image of the background from an image of the main subject and performs color corrections individually for the background and the main subject.

8. An electronic camera comprising:

an imaging device that performs photoelectric conversion on an image formed by a taking lens and outputs an image signal;

an exposure time determination unit that determines an exposure time for said imaging device based upon a subject brightness;

a light emission quantity control unit that, when performing photographing with an electronic flash unit, controls a light emission quantity by controlling a length of flash time at said electronic flash unit; and

an exposure quantity control unit that sets said exposure time roughly equal to said flash time by extending said exposure time if said flash time is longer than said exposure time.

9. An electronic camera according to claim 8, further comprising:

a signal processing unit that performs image processing on image data generated by amplifying an image signal output by said imaging device at a specific gain; and

an arithmetic operation unit that calculates a quantity of overexposure occurring due to an extension of said exposure time effected by said exposure quantity control unit, wherein;

said signal processing unit engages in, at least, either adjustment of said gain or color correction through said image processing based upon said quantity of overexposure calculated at said arithmetic operation unit.

10. An electronic camera according to claim 9, further comprising:

a data table in which processing parameters corresponding to said quantity of overexposure are stored, wherein;

said signal processing unit performs said image processing using said processing parameters read out in correspondence to said quantity of overexposure from said data table.

11. An electronic camera according to claim 9, wherein:

said signal processing unit separates an image of the background from an image of the main subject and performs color corrections individually for the background and the main subject.

12. An electronic camera comprising:

an imaging device that performs photoelectric conversion on an image formed by a taking lens and outputs an image signal;

an exposure time determination unit that determines an exposure time for said imaging device based upon a subject brightness;

a light emission quantity control unit that, when performing photographing with an electronic flash unit, controls a light emission quantity by controlling a length of flash time at said electronic flash unit; and

a photographing operation prohibiting unit that prohibits a photographing operation if said flash time is longer than said exposure time.

13. An electronic camera comprising:

an imaging device that performs photoelectric conversion on an image formed by a taking lens and outputs an image signal;

an exposure time determination unit that determines an exposure time for said imaging device based upon a subject brightness;

a light emission quantity control unit that, when performing photographing with an electronic flash unit, controls a light emission quantity by controlling a length of flash time at said electronic flash unit; and

a warning unit that transmits a warning if said flash time is longer than said exposure time.

14. An electronic camera according to claim 13, further comprising:

an light emission quantity control unit that ensures that a flash operation by said electronic flash unit is completed within said exposure time by reducing said flash time if it is detected that a release operation is performed after said warning is issued by said warning unit.

15. An electronic camera according to claim 14, further comprising:

a signal processing unit that performs image processing on image data generated by amplifying said image signal output by said imaging device at a specific gain; and

an arithmetic operation unit that calculates a quantity of underexposure occurring due to a reduction in said flash time effected by said light emission quantity control unit, wherein;

said signal processing unit engages in, at least, either adjustment of said gain or color correction through said image processing based upon said quantity of underexposure calculated at said arithmetic operation unit.

16. An electronic camera according to claim 15, further comprising:

a data table in which processing parameters corresponding to said quantity of underexposure are stored, wherein;

said signal processing unit performs said image processing using said processing parameters read out in correspondence to said quantity of underexposure from said data table.

17. An electronic camera according to claim 15, wherein:

said signal processing unit separates an image of the background from an image of the main subject and performs color corrections individually for the background and the main subject.

18. An electronic camera according to claim 13, further comprising:

an exposure quantity control unit that sets said exposure time roughly equal to said flash time by extending said exposure time if it is detected that a release operation is performed after said warning is issued by said warning unit.

19. An electronic camera according to claim 18, further comprising:

a signal processing unit that performs image processing on image data generated by amplifying an image signal output by said imaging device at a specific gain; and

an arithmetic operation unit that calculates a quantity of overexposure occurring due to an extension of said exposure time effected by said exposure quantity control unit, wherein;

said signal processing unit engages in, at least, either adjustment of said gain or color correction through said image processing based upon said quantity of overexposure calculated at said arithmetic operation unit.

20. An electronic camera according to claim 19, further comprising:

a data table in which processing parameters corresponding to said quantity of overexposure are stored, wherein;

said signal processing unit performs said image processing using said processing parameters read out in correspondence to said quantity of overexposure from said data table.

21. An electronic camera according to claim 19, wherein:

said signal processing unit separates an image of the background from an image of the main subject and performs color corrections individually for the background and the main subject.