CONTROLLING AN EXPOSURE TIME FOR DIGITAL CAMERAS

• US 20090052878A1
• Filed: 08/18/2008
• Published: 02/26/2009
• Est. Priority Date: 07/29/2005
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Pure Digital Technology Incorporated (Cisco Systems, Inc.)
• Inventors: Warpakowski Furlan, John Louis
• Granted Patent: US 8,073,321 B2
• Time in Patent Office: Days
• US Class Current: 396/6
• CPC Class Codes: G03B 15/03 Combinations of cameras with lighting apparatus; Flash units
• 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 23/55 Optical parts specially adapted for electronic image sensors; Mounting thereof
• 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
• CPC Class Codes: H04N 25/531 by controlling rolling shutters in CMOS SSIS

Abstract

Various methods, apparatuses, and systems in which a digital photography device includes a global shutter to control exposure time, a sensor array, and a flash illumination are described. The global shutter is in the optical path of light going to the sensor. The flash illumination generates a pulsed illumination. The shutter speed of the global shutter during a pre-flash illumination substantially matches the shutter speed during the flash illumination during the taking of a picture using the flash illumination based on the global shutter receiving a trigger signal from a controller.

Claims

1. A digital photography device comprising:

a sensor array configured to receive light from an object propagating along an optical path;

a mechanical global shutter disposed in the optical path and characterized by a shutter speed;

a flash configured to generate pulsed illumination; and

a controller in electrical communication with the flash, wherein the controller is configured to provide a trigger signal to the flash and wherein a shutter speed during a pre-flash illumination period is substantially equal to a shutter speed during a flash illumination period.

2. The digital photography device of claim 1 wherein the mechanical global shutter is positioned between the object and the sensor array.

3. The digital photography device of claim 1 wherein the controller is configured to provide a trigger signal to the mechanical global shutter during an ambient light period prior to the pre-flash illumination period.

4. The digital photography device of claim 3 wherein the controller is configured to determine a power level provided to the flash during the flash illumination period based on a ratio of an illumination level of the sensor array during the ambient light period and an illumination level of the sensor array during the pre-flash illumination period.

5. The digital photography device of claim 1 wherein the sensor array comprises a complementary metal-oxide semiconductor sensor implementing a rolling shutter timing mechanism.

6. The digital photography device of claim 1 wherein the digital photography device is a component of at least one of a digital camera, a one-time use digital camera, or a cellular phone.

7. The digital photography device of claim 6 wherein the one-time use digital camera further comprises an external processing unit configured to:

receive data from the sensor array;

perform image processing operations on the received data; and

convert the processed data to a formatted graphics file associated with a captured digital image.

8. The digital photography device of claim 1 wherein the controller is configured to adjust a power level provided to the flash during the flash illumination period based on an illumination level of the sensor array measured during the pre-flash illumination period.

9. The digital photography device of claim 1 wherein the controller is configured to measure an illumination level of the sensor array during an ambient condition and during the pre-flash illumination period.

10. The digital photography device of claim 9 further comprising a memory configured to store the illumination levels during the ambient condition, the pre-flash illumination period, and the flash illumination period.

11. A method of operating a digital photography device having a sensor array, a mechanical global shutter, and a flash, the method comprising:

opening the mechanical global shutter during a pre-flash illumination period characterized by a predetermined time; and

opening the mechanical global shutter during a flash illumination period characterized by the predetermined time.

12. The method of claim 11 wherein the flash illumination period is associated with acquisition of an image by the sensor array.

13. The method of claim 11 further comprising opening the mechanical global shutter during an ambient light period prior to the pre-flash illumination period.

14. The method of claim 13 wherein the ambient light period is characterized by the predetermined time.

15. The method of claim 13 further comprising determining a power level provided to the flash during the flash illumination period based on a ratio of light received by the sensor array during the ambient light period and the pre-flash illumination period.

16. A digital camera comprising:

a flash configured to generate pulsed illumination along a first optical path extending from the flash to an object to be imaged;

a lens disposed along a second optical path extending from the object toward the digital camera;

a mechanical global shutter disposed along the second optical path;

a sensor array disposed along the second optical path; and

a controller in electrical communication with the flash, the mechanical global shutter, and the sensor array, wherein the controller is configured to provide a trigger signal to open the mechanical global shutter during a pre-imaging flash period and during an imaging flash period, the pre-imaging flash period being within a factor of two of the imaging flash period.

17. The digital camera of claim 16 wherein the pre-imaging flash period is substantially equal to the imaging flash period.

18. The digital camera of claim 16 wherein the controller is further configured to provide a trigger signal to open the mechanical global shutter during an ambient light period.

19. The digital camera of claim 16 wherein the sensor array comprises a complementary metal-oxide semiconductor sensor.

20. The digital camera of claim 16 wherein the digital camera is a one-time use digital camera.