Task-based imaging systems

• US 20100278390A1
• Filed: 09/19/2006
• Published: 11/04/2010
• Est. Priority Date: 12/01/2003
• Status: Active Grant

• Current Assignee: Omnivision Technologies Incorporated (Will Semiconductor Co., Ltd. Shanghai)
• Original Assignee: Omnivision Technologies Incorporated (Will Semiconductor Co., Ltd. Shanghai)
• Inventors: Narayanswamy, Ramkumar, Johnson, Gregory E., Dowski, Edward R. JR., Silveira, Paulo E.X., Cormack, Robert H.
• Granted Patent: US 7,944,467 B2
• Time in Patent Office: Days
• US Class Current: 382/106
• CPC Class Codes: G02B 27/0025 for optical correction, e.g. distorsion, aberration
• CPC Class Codes: G06V 40/19 Sensors therefor

Abstract

A task-based imaging system for obtaining data regarding a scene for use in a task includes an image data capturing arrangement for (a) imaging a wavefront of electromagnetic energy from the scene to an intermediate image over a range of spatial frequencies, (b) modifying phase of the wavefront, (c) detecting the intermediate image, and (d) generating image data over the range of spatial frequencies. The task-based imaging system also includes an image data processing arrangement for processing the image data and performing the task. The image data capturing and image data processing arrangements cooperate so that signal-to-noise ratio (SNR) of the task-based imaging system is greater than SNR of the task-based imaging system without phase modification of the wavefront over the range of spatial frequencies.

Claims

1. A task-based imaging system for obtaining data regarding a scene for use in a task, comprising:

an image data capturing arrangement for (a) imaging a wavefront of electromagnetic energy from the scene to an intermediate image over a range of spatial frequencies, (b) modifying phase but not amplitude of the wavefront, (c) detecting the intermediate image, and (d) generating image data over the range of spatial frequencies; and

an image data processing arrangement for processing the image data and performing the task,

the image data capturing arrangement cooperating with the image data processing arrangement such that signal-to-noise ratio (SNR) of the task-based imaging system is greater than SNR of the task-based imaging system without phase modification of the wavefront over the range of spatial frequencies.

2. The task-based imaging system of claim 1, wherein the task is selected as at least one of biometric iris recognition, biometric face recognition, biometric recognition for access control, biometric recognition for threat identification, barcode reading, imaging for quality control in an assembly line, optical character recognition, biological imaging and automotive imaging for object detection.

3. A task-based imaging system for obtaining data regarding a scene for use in a task, comprising:

at least one optical element for (a) imaging a wavefront of electromagnetic energy from the scene to an intermediate image and (b) modifying phase of the wavefront; and

a first detector for detecting the intermediate image over a range of spatial frequencies,

the imaging system being configured so as not to modify amplitude of the wavefront, and the at least one optical element being configured for cooperating with the first detector so that signal-to-noise ratio (SNR) of the task-based imaging system is greater than SNR of the task-based imaging system without phase modification of the wavefront over the range of spatial frequencies.

4. The task-based imaging system of claim 3, wherein the task is selected as at least one of biometric iris recognition, biometric face recognition, biometric recognition for access control, biometric recognition for threat identification, barcode reading, imaging for quality control in an assembly line, optical character recognition, biological imaging and automotive imaging for object detection.

5. The task-based imaging system of claim 3, further comprising an image processing arrangement for performing the task.

6. The task-based imaging system of claim 5, further comprising a modulation element for modifying the phase the wavefront, wherein the modulation element and the image processing arrangement cooperate so as to reduce at least one imaging aberration in the task-based imaging system in comparison to the task-based imaging system without the modulation element and the image processing arrangement.

7. The task-based imaging system of claim 6, wherein the imaging aberration is one or more of temperature-dependent aberration and impact-induced aberration.

8. The task-based imaging system of claim 3, further comprising a second detector in electronic communication with the first detector such that the image data is transferable between the first detector and the second detector.

11. The task-based imaging system of claim 3, wherein the at least one optical element is a variable optical element.

12. The task-based imaging system of claim 11, wherein the variable optical element provides variable modification of the phase of the wavefront.

13. The task-based imaging system of claim 12, wherein the variable optical element includes at least one of adaptive optics and a spatial light modulator.

14. The task-based imaging system of claim 11, wherein the variable optical element provides variable scaling of the intermediate image.

15. The task-based imaging system of claim 11, wherein the variable optical element includes at least a selected one of a liquid lens, a liquid crystal variator, a slidable optical element configuration, a sliding variator arrangement and a sliding aperture variator.

9. A task-based imaging system for obtaining data regarding a scene for use in a task, comprising:

at least one optical element for (a) imaging a wavefront of electromagnetic energy from the scene to an intermediate image and (b) modifying phase of the wavefront; and

a first detector for detecting the intermediate image over a range of spatial frequencies,

the at least one optical element being configured for cooperating with the first detector so that signal-to-noise ratio (SNR) of the task-based imaging system is greater than SNR of the task-based imaging system without phase modification of the wavefront over the range of spatial frequencies,

wherein modifying phase is characterized by a pupil function of a form;

10. The task-based imaging system of claim 9, wherein the pupil function coefficients are given by α

(0,3)=α

(3,0)=23.394, α

(0,5)=α

(5,0)=60.108, α

(0,7)=α

(7,0)=−

126.421, α

(0,9)=α

(9,0)=82.128, α

(3,3)=5.021, α

(5,5)=−

21.418, α

(7,7)=−

310.749, and α

(9,9)=−

1100.336.

16. (canceled)

17. A method for generating an output image of a scene captured by a detector of a task-based imaging system, the detector including a plurality of pixels and the scene including at least one object located at a given object distance within a range of object distances, which object distance is defined as a distance between the object and the task-based imaging system, the method comprising:

capturing a high resolution image of the scene over a range of spatial frequencies;

converting the high resolution image into an image spectrum of the scene;

determining a defocused optical transfer function (OTF) of the task-based imaging system over the range of object distances;

determining a pixel modulation transfer function (MTF) over the plurality of pixels of the detector;

multiplying the image spectrum with the OTF and the MTF to generate a modified image spectrum of the scene;

converting the modified image spectrum into a modified image of the scene;

generating the output image from the modified image.

18. The method of claim 17, the step of generating including faulting a resized image from the modified image, and forming the output image from the resized image.

19. The method of claim 18, wherein forming the resized image includes down-sampling the modified image to a final resolution, in accordance with the given object distance.

20. The method of claim 19, wherein down-sampling includes resizing the modified image without low-pass filtering.

21. The method of claim 19, wherein down-sampling comprises:

processing the modified image for a given down-sampling origin and a down-sampling period; and

generating multiple aliased versions of the resized image by varying the down-sampling origin within the down-sampling period.

22. The method of claim 18, wherein the detector has shot noise and read noise characteristics, and wherein forming the output image comprises adding at least one of the shot noise and read noise characteristics to the resized image.

23. The method of claim 18, wherein the resized image includes at least one boundary line, the method further comprising padding the resized image by replicating the boundary line to generate a padded image with a desired image size.

24. The method of claim 17, further comprising filtering the output image with a filter kernel to generate a filtered image.

25. The method of claim 17, further comprising:

from the output image, calculating a signal-to-noise ratio (SNR) over the scene;

modifying the defocused OTF of the imaging system such that the SNR in the output image is larger than that calculated from the output image without modifying the defocused OTF.

26. The method of claim 25, further comprising:

averaging the SNR over a range of directions over the scene to generate an average SNR; and

altering the defocused OTF such that the average SNR in the output image is larger than that calculated from the output image without altering the defocused OTF.

27. The method of claim 26, wherein averaging the SNR comprises calculating a weighted average SNR over the scene.

28. The method of claim 27, wherein calculating the weighted average SNR includes varying a weighting factor of the SNR in accordance with at least a selected one of a reduction in signal strength and a reduction in incoherent imaging system modulation as a function of the given object distance.

29. The method of claim 27, further comprising setting a focus of the task-based imaging system at a position corresponding to that at which an SNR calculated for smallest and largest object distance values in the range of object distances are equal.

30. The method of claim 26, wherein altering comprises modifying the task-based imaging system to effect a pupil function of a form:

31. The method of claim 17, further comprising post-processing the output image for performing a task selected as at least one of biometric iris recognition, biometric face recognition, biometric recognition for access control, biometric recognition for threat identification, barcode reading, imaging for quality control in an assembly line, optical character recognition, biological imaging and automotive imaging for object detection.

32. A method for use with a task-based imaging system, comprising:

imaging electromagnetic energy from a scene to an intermediate image of the task-based imaging system over a range of spatial frequencies;

modifying phase but not amplitude of a wavefront of the electromagnetic energy;

detecting the intermediate image; and

generating image data over the range of spatial frequencies, based on the intermediate image such that signal-to-noise ratio (SNR) of the task-based imaging system is greater than SNR of the task-based imaging system without modifying phase over the range of spatial frequencies.

33. The method of claim 32, further comprising performing at least a selected one of analyzing an iris pattern for biometric iris recognition, analyzing a facial pattern for biometric face recognition, identifying a threat by biometric recognition, controlling access to a restricted area, imaging for quality control in an assembly line, optically recognizing alphanumeric characters, identifying features during biological imaging, imaging objects in automotive applications, and generating a viewable, final image.

34. A method for use with a task-based imaging system, comprising:

imaging electromagnetic energy from a scene to an intermediate image of the task-based imaging system over a range of spatial frequencies;

modifying phase of a wavefront of the electromagnetic energy;

detecting the intermediate image; and

generating image data over the range of spatial frequencies, based on the intermediate image such that signal-to-noise ratio (SNR) of the task-based imaging system is greater than SNR of the task-based imaging system without modifying phase over the range of spatial frequencies,

wherein modifying the phase of the wavefront comprises altering the phase with a pupil function of a form;

35. The method of claim 34, wherein the pupil function coefficients are given by α

(0,3)=α

(3,0)=23.394, α

(0,5)=α

(5,0)=60.108, α

(0,7)=α

(7,0)=−

126.421, α

(0,9)=α

(9,0)=82.128, α

(3,3)=5.021, α

(5,5)=−

21.418, α

(7,7)=−

310.749, and α

(9,9)=−

1100.336.

36. A method for optimizing a task-based imaging system for obtaining data of a scene for use in a task over a range of object distances, the scene including at least one object located at a given object distance within the range of object distances, which object distance is defined as a distance between the object and the task-based imaging system, the method comprising:

1) determining a target signal-to-noise ratio (SNR) of the task-based imaging system;

2) specifying an initial set of pupil function parameters and a merit function;

3) generating a new set of pupil function parameters based on the merit function;

4) calculating SNR over the range of object distances;

5) comparing the SNR to a target SNR; and

6) repeating steps

     2) through

     5) until the SNR is at least equal in value to the target SNR.

37. The method of claim 36,

wherein determining the target SNR comprises determining a target polar-SNR, and

wherein calculating comprises calculating a polar-SNR over the range of object distances.

38. In a task-based imaging system for obtaining data regarding a scene for use in a task, the task-based imaging system including at least one optical element for imaging a wavefront of electromagnetic energy from the scene, without modifying amplitude of the wavefront, to an intermediate image over a range of spatial frequencies, and a detector for detecting the intermediate image and for generating image data over the range of spatial frequencies, an improvement comprising:

a phase modification element for modifying phase but not amplitude of the wavefront such that signal-to-noise ratio (SNR) of the task-based imaging system is greater than a SNR of the task-based imaging system without the phase modification element.

39. In the task-based imaging system of claim 38, a further improvement comprising a processor for performing the task.

40. In the task-based imaging system of claim 39, a further improvement wherein the processor creates a record of the task, and records the record in a data storage unit.