Systems and methods for improved autofocus in digital imaging systems

• US 20070098380A1
• Filed: 11/03/2005
• Published: 05/03/2007
• Est. Priority Date: 11/03/2005
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Spielberg, Anthony
• Granted Patent: US 7,409,149 B2
• Time in Patent Office: Days
• US Class Current: 396/50
• CPC Class Codes: G03B 13/36 Autofocus systems
• CPC Class Codes: H04N 23/671 in combination with active ranging signals, e.g. using light or sound signals emitted toward objects
• CPC Class Codes: H04N 23/6812 based on additional sensors, e.g. acceleration sensors
• CPC Class Codes: H04N 23/81 for suppressing or minimising disturbance in the image signal generation

Abstract

Systems and methods to improve autofocus in digital imaging systems, such as digital cameras, are disclosed. Embodiments may include, in response to locking of lens focus on a subject image, determining an initial subject focus distance and an initial attitude, and in response to a request for an exposure, determining a final attitude. Embodiments may also include determining a final target subject distance based on the initial subject focus distance and a focus correction distance, where the focus correction distance is based on the difference between the initial attitude and the final attitude. Embodiments may also include focusing the lens at the final target subject distance. Further embodiments may include after focusing the lens at the final target subject distance, exposing an image. Other embodiments may include determining the initial and final attitude with a micro-electro-mechanical (MEMS)-based sensor or other sensor.

Claims

1. A method for autofocusing a lens of a digital imaging system, the method comprising:

in response to locking of lens focus on a subject image, determining an initial subject focus distance and an initial attitude;

in response to a request for an exposure, determining a final attitude;

determining a final target subject distance based on the initial subject focus distance and a focus correction distance, the focus correction distance being based on the difference between the initial attitude and the final attitude; and

focusing the lens at the final target subject distance.

2. The method of claim 1, further comprising activating autofocus correction.

3. The method of claim 1, further comprising after focusing the lens at the final target subject distance, exposing an image.

4. The method of claim 1, wherein determining an initial attitude comprises determining an initial attitude with respect to the earth'"'"'s gravimetric field.

5. The method of claim 1, wherein determining a final attitude comprises determining a final attitude with respect to the earth'"'"'s gravimetric field.

6. The method of claim 1, wherein determining a final target subject distance comprises:

determining a focus correction distance based on the initial subject focus distance and the difference between the initial attitude and the final attitude; and

modifying the initial subject focus distance by the subtracting the determined focus correction distance to determine a final target subject distance.

7. The method of claim 1, wherein focusing the lens at the final target subject distance comprises driving the lens a distance based on the focus correction distance.

8. A digital imaging system, the system comprising:

a user interface module, the user interface module being adapted to receive focus lock commands and exposure commands from a user;

an image capture module to generate a digital image; and

an autofocus system module to automatically focus a lens, the autofocus module comprising;

a primary autofocus system to determine whether the lens is in focus;

an attitude sensor interface, the attitude sensor interface being adapted to receive an indication of an initial attitude in response to an focus lock command and a final attitude in response to an exposure command;

an autofocus correction module to determine a focus correction distance based on the initial attitude and the final attitude; and

wherein the primary autofocus system corrects lens focus based on the focus correction distance before an exposure is made.

9. The system of claim 8, further comprising a focusing motor controller of the autofocus system module to modify the lens focus.

10. The system of claim 8, wherein the primary autofocus system is adapted to determine an initial target subject distance in response to receiving a focus lock command.

11. The system of claim 8, wherein the autofocus correction module is adapted to, in response to an exposure command, determine a final target subject distance based on an initial target subject distance and the focus correction distance.

12. A digital imaging system, the system comprising:

a housing;

a processor within the housing to control operation of the digital imaging system;

an optical sensor array within the housing and in communication with the processor, the optical sensor array being adapted to generate an image in response to light;

an autofocus system in communication with the processor;

a attitude sensor in communication with the processor, the attitude sensor being adapted to determine an initial attitude in response to a focus lock command and a final attitude in response to a shutter release command; and

wherein the processor is adapted to execute a series of operations to determine a focus correction distance based on the difference between the initial attitude and the final attitude, wherein the processor is further adapted to execute a series of operations to modify focus based on the focus correction distance.

13. The system of claim 12, further comprising a lens permanently mounted to the housing to focus light from outside the digital imaging system traversing a light path to the optical sensor array.

14. The system of claim 12, further comprising a lens attached to the housing to focus light from outside the digital imaging system traversing a light path to the optical sensor array.

15. The system of claim 12, further comprising a focusing motor in communication with the processor, the autofocus motor being adapted to move a lens to change its point of focus.

16. The system of claim 12, further comprising one or more autofocus sensors in communication with the processor.

17. The system of claim 12, wherein the digital imaging system is a digital camera.

18. The system of claim 12, wherein the attitude sensor is a micro-electro-mechanical (MEMS) sensor.

19. The system of claim 12, wherein the attitude sensor is further adapted to distinguish between a portrait orientation and a landscape orientation.

20. The system of claim 12, wherein the attitude sensor is one or more of a gyroscope or inertial measurement unit (IMU).