Electronic camera for producing an image having a wide dynamic range

• US 6,753,920 B1
• Filed: 08/27/1999
• Issued: 06/22/2004
• Est. Priority Date: 08/28/1998
• Status: Expired due to Fees

• Current Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Original Assignee: Olympus Optical Corporation Limited (Olympus Corporation)
• Inventors: Fukuda, Hidetoshi, Koseki, Hiroaki, Inagaki, Osamu, Kakinuma, Minoru, Momose, Takumi
• Primary Examiner(s): Vu, Ngoc-Yen, VU, NGOC YEN T
• Application Number:
  US09/384,414
• Time in Patent Office: 1,761 Days
• Field of Search: 348/221.1, 348/222.1, 348/223.1, 348/224.1, 348/229.1, 348/230.1, 348/362-367, 348/370, 348/371, 396/61, 396/62
• US Class Current: 348/371
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means

Abstract

An electronic camera for producing a composite image having a wide dynamic range and a high quality by composing first and second image signals obtained by picking-up an object successively two times with first and second stroboscopic flash exposures having a predetermined exposure amount ratio, including a CCD image sensing element, a stroboscopic flash device, and a flash light control circuit for controlling an excited emission of said stroboscopic flash device. At an end of the first exposure, the excited light emission from the stroboscopic flash device is temporarily stopped, but an excited condition of the stroboscopic flash device is kept. During this very short light emission interruption period, electrostatic charges stored in a light receiving section of the CCD image sensing element during the first exposure are transferred into a vertical transfer section. After that, the excited flash light is emitted again to perform the second exposure without recharging a trigger capacitance.

Claims

1. An electronic camera producing an image having a wide dynamic range by composing two image signals obtained by picking-up an object two times successively with different exposure amounts, comprising:

an image picking-up means including a solid state image sensing element for picking-up an object to derive an image signal;

a flash light emitting means for irradiating said object with flash light;

an image signal composing means for composing two image signals obtained by picking-up the object two times with a desired exposure amount ratio; and

a flash light emission controlling means for controlling an excited emission of said flash light emitting means in accordance with said desired exposure amount ratio such that upon the first exposure, said flash light emitting means is excited and the flash light is emitted, an excited condition of the flash light emitting means is kept over said second exposure, and after once stopping the light emission at an end of the first exposure, the flash light is emitted again to perform the second exposure.

2. An electronic camera as claimed in claim 1, wherein said flash light emitting means is controlled by said flash light emission controlling means such that flash light is emitted from said flash light emitting means in each of said first and second exposures.

3. An electronic camera as claimed in claim 1, further comprising a mechanical shutter which is closed at the end of the second exposure and is kept to be closed at least until the image signals obtained for the first and second exposures are read out of the solid state image sensing element.

4. An electronic camera as claimed in claim 1, wherein said flash light emission controlling means determines excited light emission time periods for the first and second exposures such that exposure amounts of the first and second exposures correspond to said desired exposure amount ratio between the first exposure and the second exposure.

5. An electronic camera as claimed in claim 1, wherein an exposure amount of said first exposure is smaller than an exposure amount of said second exposure.

6. An electronic camera as claimed in claim 5, wherein said exposure amount of the second exposure corresponds to a desired exposure amount for the object.

7. An electronic camera as claimed in claim 1, wherein said image picking-up means is constructed such that electrostatic charges stored in a light receiving section of the solid state image sensing element during the first exposure are transferred into a vertical transfer section of the solid state image sensing element during the time interval between the first exposure and the second exposure during which the excited light emission is temporarily interrupted.

8. An electronic camera as claimed in claim 7, wherein said flash light emission controlling means includes an exposure control table which represents a plurality of exposure control data values for the first exposure and a plurality of exposure control data values for the second exposure, said exposure control data values determining excited light emission times for the first and second exposures in accordance with said predetermined exposure amount ratio, and the excitation light emission is controlled by selecting, from said exposure control table, exposure control data values corresponding to an image picking-up condition.

9. An electronic camera as claimed in claim 8, wherein said plurality of exposure control data values for the first and second exposures are constructed by exposure control data values for a conventional single exposure in which no image composition is carried out.

10. An electronic camera as claimed in claim 8, wherein said image picking-up means includes a variable stop which is controlled in accordance with a distance from the camera to the object, and exposure control data values for the first and second exposures are selected from said exposure control table on the basis of a stop value of the variable stop.

11. An electronic camera as claimed in claim 8, wherein said exposure amount ratio between the first exposure and the second exposure is predetermined.

12. An electronic camera as claimed in claim 8, wherein said exposure amount ratio between the first exposure and the second exposure is determined in accordance with the image picking-up condition.

13. An electronic camera as claimed in claim 8, wherein said flash light emitting means comprises a flash light source, a trigger capacitance for triggering said flash light source into the excited condition, and a light emission capacitance for supplying a light emitting energy to said flash light source in the excited condition to emit an excited light, whereby said exposure control data values for the first exposure in said exposure control table of said flash light emission controlling means are determined on the basis of a reference voltage of said light emission capacitance, and said exposure control data values for the second exposure are determined on the basis of a voltage across said light emission capacitance which is determined by considering a voltage drop due the excited light emission for the first exposure.

14. An electronic camera as claimed in claim 13, wherein said flash light emitting means further comprises a switching element connected in series with said flash light emitting means and light emission capacitance, and said flash light emission controlling means supplies a light emission stop signal during said time interval between the first exposure and the second exposure to said switching element and switching element is cut off for said time interval to stop the emission of the excited flash light.

15. An electronic camera as claimed in claim 14, wherein said time interval during which said switching element is cut off is set to a value from about 5 μ

sec to about 30 μ

sec.

16. An electronic camera as claimed in claim 13, wherein said flash light emission controlling means includes a voltage detecting means for detecting a voltage across said light emission capacitance, and the excited light emission is controlled by selecting, from said exposure control table, exposure control data values for the first and second exposures suitable for an exposure condition on the basis of a comparison of the detected voltage with the reference voltage.

17. An electronic camera producing an image having a wide dynamic range by composing two image signals obtained by picking-up an object two times successively with different exposure amounts, comprising:

an image picking-up unit including a solid state image sensing element for picking-up an object to derive an image signal;

a flash light emitting unit for irradiating said object with flash light;

an image signal composing unit for composing two image signals obtained by picking-up the object two times with a desired exposure amount ratio; and

a flash light emission controlling unit for controlling an excited emission of said flash light emitting unit in accordance with said desired exposure amount ratio and storing an exposure control table which includes a plurality of exposure control data values for the first exposure and a plurality of exposure control data values for the second exposure, and the excitation light emission is controlled by selecting, from said exposure control table, exposure control data values corresponding to an image picking-up condition, wherein;

said flash light emitting unit comprises a flash light source, a trigger capacitance for triggering said flash light source into the excited condition, and a light emission capacitance for supplying a light emitting energy to said flash light source in the excited condition to emit an exited light, and

said exposure control data values for the first exposure in said exposure control table of said flash light emission controlling unit are determined on the basis of a reference voltage of said light emission capacitance, and said exposure control data values for the second exposure are determined on the basis of a voltage across said light emission capacitance which is determined by considering a voltage drop due to the excited light emission for the first exposure.

18. The electronic camera according to claim 17, wherein said flash light emitting unit further comprises a switching element connected in series with said flash light emitting unit and light emission capacitance, and said flash light emission controlling unit supplies a light emission stop signal during a time interval between the first exposure and the second exposure to said switching element and the switching element is cut off for said time interval to stop the emission of the excited flash light.

19. The electronic camera according to claim 18, wherein said time interval during which said switching element is cut off is set to a value from about 5 usec to about 30 usec.

20. The electronic camera according to claim 17, wherein said flash light emission controlling unit includes a voltage directing means for detecting a voltage across said light emission capacitance, and the excited light emission is controlled by selecting, from said exposure control table, exposure control data values for the first and second exposures suitable for an exposure condition on the basis of a comparison of the detected voltage with the reference voltage.