Infra-red (IR) sensor with controllable sensitivity

• US 7,928,395 B2
• Filed: 08/11/2004
• Issued: 04/19/2011
• Est. Priority Date: 10/02/2003
• Status: Expired due to Fees

• Current Assignee: Opgal
• Original Assignee: Opgal
• Inventors: Grimberg, Ernest
• Primary Examiner(s): Porta; David P
• Assistant Examiner(s): Malevic; Djura
• Application Number:
  US10/574,462
• Publication Number:
  US 20070018105A1
• Time in Patent Office: 2,442 Days
• Field of Search: 250/349
• US Class Current: 250/349
• CPC Class Codes: G01J 2005/0077 Imaging
• CPC Class Codes: G01J 5/22 Electrical features thereof
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/72 Combination of two or more compensation controls
• CPC Class Codes: H04N 25/443 by reading pixels from selected 2D regions of the array, e.g. for windowing or digital zooming
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

An infrared sensor contains a sensor array and a sensitivity adjuster. The sensor array collects IR energy from an external scene, and the sensitivity adjuster adjusts a pixel grouping for light collection and/or readout, so that the resulting IR image is available at a required sensitivity level.

Claims

1. An infrared sensor comprising:

a sensor array comprising multiple IR sensors, configured for collecting IR energy from an external scene;

an image processor, configured for processing a sensor array output signal to obtain an IR image, for analyzing said image to determine a property of said IR image, said property being indicative of image quality, and for generating a feedback signal in accordance with said property if said property crosses a threshold, said feedback signal being for adjusting between a field of view and a grouping of sensing pixels so as to derive a required image sensitivity; and

a sensitivity adjuster associated with said sensor array, configured for deriving said required image sensitivity by adjusting between said field of view and said grouping of sensing pixels in accordance with said feedback signal.

2. An IR sensor in accordance with claim 1, wherein said sensor array comprises an array of photon detectors.

3. An IR sensor in accordance with claim 1, wherein said sensor array comprises an infrared focal plane assembly (IRFPA).

4. An IR sensor in accordance with claim 1, wherein said sensitivity adjuster comprises a window selector configured for selecting a readout window within said array.

5. An IR sensor in accordance with claim 4, further comprising a mode selector configured for switching between a small readout region and a large readout region in accordance with said feedback signal, respectively to provide high-sensitivity and low-sensitivity imaging.

6. An IR sensor in accordance with claim 1, wherein said sensitivity adjuster comprises a grouping factor selector configured for selecting a pixel grouping factor during IR energy collection.

7. An IR sensor in accordance with claim 6, further comprising a mode selector configured for switching between a large pixel grouping and a small pixel grouping in accordance with said feedback signal, respectively to provide high-sensitivity and low-sensitivity imaging.

8. An IR sensor in accordance with claim 1, further comprising a readout element configured for performing periodic sensor array readout with a readout time variable with a size of a selected readout window.

9. An IR sensor in accordance with claim 1, wherein said adjusting is in accordance with externally provided control information.

10. An IR sensor in accordance with claim 1, wherein said property indicative of image quality comprises image SNR, and wherein said image processor further comprises an SNR detector configured for detecting an SNR of said IR image.

11. An IR sensor in accordance with claim 1, wherein said property indicative of image quality comprises image contrast, and wherein said image processor further comprises a contrast detector, configured for detecting a contrast level of said IR image.

12. An IR sensor in accordance with claim 1, further comprising a mode selector configured for switching between a high-sensitivity operating mode and a low-sensitivity operating mode in accordance with said feedback signal.

13. An IR sensor in accordance with claim 1, further comprising a video processor, configured for processing a sensor array output to form a video image.

14. An IR sensor in accordance with claim 1, wherein said property comprises image SNR.

15. An IR sensor in accordance with claim 1, wherein said property comprises image contrast.

16. An IR sensor in accordance with claim 1, wherein said feedback signal comprises at least one of:

average image SNR, maximum image SNR, minimum image SNR, average image contrast, maximum image contrast, and minimum image contrast.

17. A method for IR sensing, comprising:

performing a readout of a sensor array;

processing said sensor array readout to obtain an IR image;

determining a property of said IR image, said property being indicative of image quality;

generating a feedback signal in accordance with said property, said feedback signal being for adjusting between a field of view and a grouping of sensing pixels so as to derive a required image sensitivity;

if said property crosses a specified threshold, adjusting between field of view and said pixel grouping of said sensor array to provide said required image sensitivity in accordance with said feedback signal; and

collecting IR energy over a variable window from an external scene with said sensor array, in accordance with said pixel grouping.

18. A method in accordance with claim 17, further comprising selecting a sensor exposure time.

19. A method in accordance with claim 18, wherein said selecting is to maintain an average collected charge of said sensor at a specified level.

20. A method in accordance with claim 18, wherein said method is performed repetitively at a maximum rate permitted by said pixel grouping and said selected exposure time.

21. A method in accordance with claim 17, wherein said property comprises at least one of:

average image SNR, maximum image SNR, minimum image SNR, average image contrast, maximum image contrast, and minimum image contrast.

22. A method in accordance with claim 17, further comprising averaging respective sensor levels over multiple sensor array readout cycles.

23. A method in accordance with claim 17, further comprising switching between a high-sensitivity operating mode and a low-sensitivity operating mode.

24. A method in accordance with claim 17, further comprising analyzing a video IR image to identify specified properties of interest.

25. A method in accordance with claim 17, wherein said property comprises image SNR.

26. A method in accordance with claim 17, wherein said property comprises image contrast.