Digital camera, having a flash unit, which determines proper flash duration through an assessment of image luminance and, where needed, a preliminary flash emission

• US 6,195,127 B1
• Filed: 07/16/1997
• Issued: 02/27/2001
• Est. Priority Date: 07/18/1996
• Status: Expired due to Term

• Current Assignee: Xacti Corporation (Office Support KK)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Sugimoto, Kazuhiko
• Primary Examiner(s): Garber, Wendy
• Assistant Examiner(s): White, Mitchell
• Application Number:
  US08/895,405
• Time in Patent Office: 1,322 Days
• Field of Search: 348/362, 348/364, 348/367, 348/370, 348/371, 348/234, 396/157, 396/159, 396/161, 396/391
• US Class Current: 348/370
• CPC Class Codes: G03B 7/16 in accordance with both the intensity of the flash source and the distance of the flash source from the object, e.g. in accordance with the "guide number" of the flash bulb and the focusing of the camera
• CPC Class Codes: H04N 23/73 by influencing the exposure time
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means

Abstract

A digital camera includes a flash lamp and a CCD imager. A microcomputer first exposes the CCD imager without a light-emission of the flash lamp. Therefore, a luminance evaluation value is calculated by a calculator on the basis of a luminance signal included in a camera signal generated by the CCD imager. The microcomputer succeedingly makes the flash lamp perform a preliminary light-emission, and exposes the CCD imager by {fraction (1/1500)} seconds. The calculator evaluates the luminance evaluation value on the basis of the luminance signal included in the camera signal obtained at this time. Then, the microcomputer calculates a major light-emission amount of the flash lamp on the basis of the two luminance evaluation values obtained in such a manner.

Claims

1. A digital camera for taking a picture of an object by making a flash lamp perform a major light-emission with a major light-emission amount and exposing a picture taking means for a first period, comprising:

a detection means for detecting a luminance signal from a camera signal outputted from said picture taking means;

an evaluation means for evaluating said luminance signal and outputting a luminance evaluation value;

a first control means for exposing said picture taking means without a light-emission of said flash lamp;

a second control means for making said flash lamp perform a preliminary light-emission with a preliminary light-emission amount and exposing said picture taking means for a second period shorter than said first period; and

a calculation means for calculating said major light-emission amount on the basis of a first non-emission luminance evaluation value outputted from said evaluation means in response to a control of said first control means and a preliminary light-emission luminance evaluation value outputted from said evaluation means in response to a control of said second control means;

wherein;

said first control means exposes said picture taking means for a third period; and

said calculation means includes a luminance evaluation value calculation means for calculating a second non-emission luminance evaluation value in exposing said picture taking means for said first period without the light-emission of said flash lamp, on the basis of said first period, said third period and said first non-emission luminance evaluation value, and a light-emission amount calculation means for calculating said major light-emission amount on the basis of said second non-emission luminance evaluation value, a target luminance evaluation value, said preliminary light-emission luminance evaluation value and said preliminary light-emission amount.

3. A digital camera according to claim 1, further comprising:

an exposure period calculation means for calculating a most suitable exposure period that said target luminance evaluation value is obtained without the light-emission of said flash lamp on the basis of said third period, said first preliminary light-emission luminance evaluation value and said target luminance evaluation value;

a comparison means for comparing said most suitable exposure period and a longest exposure period; and

a cancellation means for canceling said major light-emission in a case where said most suitable exposure period is shorter than said longest exposure period.

2. A digital camera according to clam 1, wherein

said luminance evaluation value calculation means calculates said second non-emission luminance evaluation value in accordance with a following equation (1),

4. A digital camera for taking a picture of an object by making a flash lamp perform a major light-emission with a major light-emission amount and exposing a picture taking means for a first period, comprising:

a detection means for detecting a luminance signal from a camera signal outputted from said picture taking means;

an evaluation means for evaluating said luminance signal and outputting a luminance evaluation value;

a first control means for exposing said picture taking means without a light-emission of said flash lamp;

a second control means for making said flash lamp perform a preliminary light-emission with a preliminary light-emission amount and exposing said picture taking means for a second period shorter than said first period; and

a calculation means for calculating said major light-emission amount on the basis of a first non-emission luminance evaluation value outputted from said evaluation means in response to a control of said first control means and a preliminary light-emission luminance evaluation value outputted from said evaluation means in response to a control of said second control means;

wherein said second period is longer than a period necessary for said preliminary light-emission.

5. A digital camera for taking a picture of an object by making a flash lamp perform a major light-emission with a major-light emission amount and exposing a picture taking means, the camera comprising:

a detection means for detecting a luminance signal from a camera signal outputted from said picture taking means;

an evaluation means for evaluating said luminance signal and outputting a luminance evaluation value;

a first control means for exposing said picture taking means without a light-emission of said flash lamp;

a second control means for making said flash lamp perform a preliminary light-emission with a preliminary light-emission amount and exposing said picture taking means;

a calculation means for calculating said major light-emission amount on the basis of a non-emission luminance evaluation value outputted from said evaluation means in response to a control of said first control means, a preliminary light-emission luminance evaluation value outputted from said evaluation means in response to a control of said second control means, a target luminance evaluation value and said preliminary light-emission value; and

a third control means for making said flash lamp perform said major light-emission with said major light-emission amount and exposing said picture taking means for a first period;

wherein said first control means exposes said picture taking means for a second period shorter than said first period, and said calculation means includes a multiplying means for multiplying said non-emission luminance value by said first period, and a dividing means for dividing a multiplication value produced by said multiplying means by said second period.

6. A digital camera for taking a picture of an object by making a flash lamp perform a major light-emission with a major light-emission amount and exposing a picture taking means for a first period, the camera comprising:

a detection means for detecting a luminance signal from a camera signal outputted from said picture taking means;

an evaluation means for evaluating said luminance signal and outputting a luminance evaluation value;

a first control means for exposing said picture taking means without a light-emission of said flash lamp;

a second control means for making said flash lamp perform a preliminary light-emission with a preliminary light-emission amount and exposing said picture taking means for a second period shorter than said first period and longer than a period necessary for said preliminary light-emission; and

a calculation means for calculating said major light-emission amount on the basis of a non-emission luminance evaluation value outputted from said evaluation means in response to a control of said first control means and a preliminary light-emission luminance evaluation value outputted from said evaluation means in response to a control of said second control means.