Electronic still camera capable of removing noise component in image data and signal processing method thereof

• US 7,136,100 B1
• Filed: 08/16/2000
• Issued: 11/14/2006
• Est. Priority Date: 09/08/1999
• Status: Expired due to Term

• Current Assignee: Casio Computer Company Limited
• Original Assignee: Casio Computer Company Limited
• Inventors: Kato, Yoshiyuki, Murata, Noriyasu, Yuyama, Masami
• Primary Examiner(s): Srivastava, Vivek
• Assistant Examiner(s): Aggarwal, Yogesh
• Application Number:
  US09/639,922
• Time in Patent Office: 2,281 Days
• Field of Search: 348/241, 348362-367, 348/221.1, 348/296, 348/243, 348/244
• US Class Current: 348/241
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/71 Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors

Abstract

Upon depression of a shutter key of a key input unit, a sensed image (DATA1) is captured by exposing a CCD for exposure time T1 with a mechanical shutter opened, and a dark frame image (DATA2) is captured by exposing the CCD for exposure time Ta with the mechanical shutter closed. A correction value corresponding to exposure time T1 is then determined by looking up a correction data table stored in a storage area of a data memory, and DATA2 is corrected using the determined correction value. By subtracting the corrected DATA2 from DATA1, a dark output component contained in DATA1 is removed.

Claims

1. An electronic still camera comprising:

image sensing means for accumulating a charge corresponding to incoming light, converting the accumulated charge into image data, and outputting the image data;

optical path opening/closing means for opening/closing an incoming optical path to said image sensing means;

acquisition means for acquiring a first exposure time;

discrimination means for determining if the first exposure time is not less than a predetermined second exposure time;

image sensing instruction means for instructing image sensing;

first image sensing control means for, when image sensing is instructed by said image sensing instruction means, capturing first image data by exposing said image sensing means for the first exposure time with said optical path opening/closing means opened;

second image sensing control means for, when image sensing is instructed by said image sensing instruction means and when the discrimination means determines that the first exposure time is not less than the second exposure time, capturing second image data by exposing said image sensing means for the second exposure time not more than the first exposure time with said optical path opening/closing means closed;

first correction means for correcting the second image data captured by said second image sensing control means; and

second correction means for correcting the first image data captured by said first image sensing control means using the second image data corrected by said first correction means.

2. A camera according to claim 1, further comprising:

a shutter switch,

wherein said image sensing instruction means instructs image sensing when said shutter switch is depressed.

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

measurement means for measuring a brightness of an object,

wherein said first exposure time corresponds to a measurement result of said measurement means.

4. A camera according to claim 1, further comprising:

setting means for setting an exposure time of user'"'"'s choice,

wherein said first exposure time is set by said setting means.

5. A camera according to claim 1, wherein said second correction means corrects the first image data by subtracting the second image data corrected by said first correction means from the first image data.

6. A camera according to claim 1, wherein said first correction means corrects the second image data captured by said second image sensing control means in accordance with the first exposure time.

7. A camera according to claim 6, further comprising:

correction table storage means for storing a correction value in correspondence with an exposure time,

wherein said first correction means reads out a correction value corresponding to the first exposure time from said correction table storage means, and corrects the second image data using the readout correction value.

8. A camera according to claim 6, wherein said second exposure time is a fixed time.

9. A camera according to claim 1, wherein said second exposure time corresponds to the first exposure time.

10. A camera according to claim 9, wherein said first correction means corrects the second image data captured by said second image sensing control means using a fixed correction value.

11. A camera according to claim 1, wherein said second exposure time corresponds to the first exposure time with said optical path opening/closing means closed, and

said first correction means corrects the second image data captured by said second image sensing control means in accordance with the first exposure time.

12. A camera according to claim 1, further comprising:

fourth image sensing control means for, when said image sensing instruction means instructs image sensing, controlling said first image sensing control means to capture the first image data, and then controlling said second image sensing control means to capture the second image data.

13. A camera according to claim 1, further comprising:

image data storage means for storing the second image data captured by said second image sensing control means,

wherein said first correction means corrects the second image data stored in said image data storage means.

14. A camera according to claim 1, further comprising;

gamma correction means for making gamma correction of image data output from said image sensing means,

wherein said first correction means corrects the second image data by changing a gamma correction characteristic of said gamma correction means.

15. A camera according to claim 1, further comprising;

adjustment means for adjusting a signal level of image data output from said image sensing means,

wherein said first correction means corrects the second image data by changing a signal adjustment level of said adjustment means.

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

third image sensing control means for, when image sensing is instructed by said image sensing instruction means and when the discrimination means determines that the first exposure time is less than the second exposure time, capturing third;

image data by exposing said image sensing means for the first exposure time with said optical path opening/closing means closed; and

third correction means for correcting said first image data captured by said first image sensing control means using the third image data captured by said third image sensing control means.

16. An electronic still camera comprising:

an image sensing element for accumulating a charge corresponding to incoming light, converting the accumulated charge into image data, and outputting the image data;

an optical path opening/closing member for opening/closing an incoming optical path to said image sensing element;

acquisition means for acquiring a first exposure time;

discrimination means for determining if the first exposure time is not less than a predetermined second exposure time;

an image sensing instruction member for instructing image sensing;

first image sensing control means for capturing first image data by exposing said image sensing element for the first exposure time with said optical path opening/closing member opened, upon depression of said image sensing instruction member;

second image sensing control means for capturing second image data by exposing said image sensing element for the second exposure time not more than the first exposure time with said optical path opening/closing member closed, upon depression of said image sensing instruction member, and when the discrimination means determines that the first exposure time is not less than the second exposure time;

first correction means for correcting the second image data captured by said second image sensing control means; and

second correction means for correcting the first image data captured by said first image sensing control means using the second image data corrected by said first correction means.

17. A signal processing method for an electronic still camera for removing a noise component in image data output from an image sensing element, said method comprising;

acquiring a first exposure time;

determining if the first exposure time is not less than a predetermined second exposure time;

capturing first image data by exposing the image sensing element for the first exposure time with an incoming optical path to the image sensing element opened, when image sensing is instructed;

capturing second image data by exposing the image sensing element for the second exposure time not more than the first exposure time with the incoming optical path to the image sensing element closed, when image sensing is instructed, and when it is determined that the first exposure time is not less than the second exposure time;

correcting the captured second image data; and

correcting the captured first image data using the corrected second image data.

19. An electronic still camera comprising:

image sensing means for accumulating a charge corresponding to incoming lights converting the accumulated charge into image data and outputting the image data;

optical path opening/closing means for opening/closing an incoming optical path to said image sensing means;

acquisition means for acquiring a first exposure time;

discrimination means for determining if the first exposure time is not less than a predetermined second exposure time;

image sensing instruction means for instructing image sensing;

first image sensing control means for, when image sensing is instructed by said image sensing instruction means, capturing first image data by exposing said image sensing means for the first exposure time with said optical path opening/closing means opened;

second image sensing control means for, when image sensing is instructed by said image sensing instruction means and when the discrimination means determines that the first exposure time is not less than the second exposure time, capturing second image data by exposing said image sensing means for the second exposure time not more than the first exposure time with said optical path opening/closing means closed;

third image sensing control means for, when image sensing is instructed by said image sensing instruction means and when the discrimination means determines that the first exposure time is less than the second exposure time, capturing third image data by exposing said image sensing means for the first exposure time with said optical path opening/closing means closed;

first correction means for correcting the second image data captured by said second image sensing control means;

second correction means for correcting the first image data captured by said first image sensing control means using the second image data corrected by said first correction means; and

third correction means for correcting the first image data captured by said first image sensing control means using the third image data captured by said third image sensing control means.

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

a shutter switch,

wherein said image sensing instruction means instructs image sensing when said shutter switch is depressed.

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

measurement means for measuring brightness of an object,

wherein said first exposure time corresponds to a measurement result of said measurement means.

22. An electronic still camera according to claim 19, wherein said second correction means corrects the first image data by subtracting the second image data corrected by said first correction means from the first image data;

and

wherein said third correction means corrects the first image data by subtracting the third image data captured by said third image sensing control means from the first image data.

23. An electronic still camera according to claim 19, wherein said first correction means corrects the second image data captured by said second image sensing control means in accordance with the first exposure time.

24. An electronic still camera according to claim 23, further comprising:

correction table storage means for storing a correction value in correspondence with an exposure time,

wherein said first correction means reads out a correction value corresponding to the first exposure time from said correction table storage means, and corrects the second image data using the correction value.

25. An electronic still camera according to claim 23, wherein said second exposure time is fixed.

26. An electronic still camera according to claim 19, further comprising fourth image sensing control means for, when image sensing is instructed by said image sensing instruction means, controlling said first image sensing control means to capture the first image data, and then one of:

(i) controlling said second image sensing control means to capture the second image data and (ii) controlling said third image sensing control means to capture the third image data.

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

image data storage means for storing the second image data captured by said second image sensing control means,

wherein said first correction means corrects the second image data stored in said image data storage means.

28. An electronic still camera comprising:

an image sensing element which accumulates a charge corresponding to incoming light, converts the accumulated charge into image data and outputs the image data;

an optical path opening/closing member which opens/closes an incoming optical path to said image sensing element

an acquisition unit which acquires a first exposure time;

a discrimination unit which determines if the first exposure time is not less than a predetermined second exposure time;

an image sensing instruction member which instructs image sensing;

first image sensing control means for, when said image sensing instruction member is depressed, capturing first image data by exposing said image sensing element for the first exposure time acquired by said acquisition unit with said optical path opening/closing member opened;

second image sensing control means for, when said image sensing instruction member is depressed and when the discrimination unit determines that the first exposure time is not less than the second exposure time, capturing second image data by exposing said image sensing element for the second exposure time not more than the first exposure time with said optical path opening/closing member closed;

third image sensing control means for, when said image sensing instruction member is depressed and when the discrimination unit determines that the first exposure time is less than the second exposure time, capturing third image data by exposing said image sensing element for the first exposure time with said optical path opening/closing member closed;

first correction means for correcting the second image data captured by said second image sensing control means;

second correction means for correcting the first image data captured by said first image sensing control means using the second image data corrected by said first correction means; and

third correction means for correcting the first image data captured by said first image sensing control means using the third image data captured by said third image sensing control means.

29. A signal processing method for an electronic still camera for removing a noise component in image data output from an image sensing element, said method comprising:

acquiring a first exposure time;

determining if the acquired first exposure time is not less than a predetermined second exposure time;

capturing first image data by exposing said image sensing element for the first exposure time with an incoming optical path to the image sensing element opened, when image sensing is instructed;

capturing second image data by exposing said image sensing element for the second exposure time not more than the first exposure time with said incoming optical path closed, when image sensing is instructed and when it is determined that the first exposure time is not less than the second exposure time;

capturing third image data by exposing said image sensing element for the first exposure time with said incoming optical path to the image sensing element closed, when image sensing is instructed and when it is determined that the first exposure time is less than the second exposure time;

correcting the captured second image data;

correcting the captured first image data using the corrected second image data; and

correcting the captured first image data using the captured third image data.