Radiometric correction and alignment techniques for thermal imager with non-contact temperature sensor

• US 10,598,550 B2
• Filed: 02/15/2018
• Issued: 03/24/2020
• Est. Priority Date: 02/17/2017
• Status: Active Grant

• Current Assignee: Teledyne FLIR LLC (Teledyne Technologies Incorporated)
• Original Assignee: FLIR Systems, Inc. (Teledyne Technologies Incorporated)
• Inventors: Christel, Roderick C., Hoelter, Theodore R., Elmfors, Per
• Primary Examiner(s): Green, Yara B
• Application Number:
  US15/898,167
• Publication Number:
  US 20180238740A1
• Time in Patent Office: 768 Days
• CPC Class Codes: G01J 2005/0077 Imaging
• CPC Class Codes: G01J 5/026 Control of working procedures of a pyrometer, other than calibration; Bandwidth calculation; Gain control
• CPC Class Codes: G01J 5/0275 Control or determination of height or distance or angle information for sensors or receivers
• CPC Class Codes: G01J 5/0804 Shutters
• CPC Class Codes: G01J 5/10 using electric radiation detectors
• CPC Class Codes: G01J 5/20 using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
• CPC Class Codes: G01J 5/53 Reference sources, e.g. standard lamps; Black bodies
• CPC Class Codes: G01J 5/532 using a reference heater of the emissive surface type, e.g. for selectively absorbing materials
• CPC Class Codes: G01J 5/80 Calibration using comparison with reference sources G01J5/52
• CPC Class Codes: H04N 23/23 from thermal infrared radiation
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors
• 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

Various techniques are provided for calibrating a thermal imaging device using a non-contact temperature sensor. In one example, a method includes capturing a thermal image of a scene. The thermal image comprises a plurality of pixel values. The method also includes detecting, by a non-contact temperature sensor, a temperature value associated with a portion of the scene corresponding to a subset of the pixel values. The method also includes comparing the subset of pixel values with the detected temperature value. The method also includes generating a correction term based on the comparing. The method also includes applying the correction term to at least the subset of pixel values to radiometrically calibrate the subset of pixel values. Related systems and alignment processes are also provided.

Claims

1. A method comprising:

capturing a thermal image of a scene by an array of infrared sensors of an imaging system, wherein the thermal image comprises a plurality of pixel values;

detecting, by a non-contact temperature sensor, a temperature value associated with a portion of the scene;

determining an alignment of the temperature sensor relative to the array;

identifying a correspondence between the portion of the scene and a subset of the pixel values based on the alignment of the temperature sensor relative to the array;

comparing the subset of pixel values with the detected temperature value;

generating a correction term based on the comparing; and

applying the correction term to at least the subset of pixel values to radiometrically calibrate the subset of pixel values.

2. The method of claim 1, wherein the applying comprises applying the correction term to all of the pixel values of the thermal image to radiometrically calibrate all of the pixel values.

3. The method of claim 1, wherein the correction term is at least one of an offset correction term and/or a gain correction term.

4. The method of claim 1, further comprising repeating the capturing, detecting, comparing, and generating to generate a plurality of correction terms associated with different temperatures.

5. The method of claim 1, wherein:

the imaging system further comprises the temperature sensor.

6. The method of claim 1, wherein the correspondence is based on at least a distance from the imaging system to the portion of the scene and the alignment of the temperature sensor relative to the array.

7. The method of claim 1, wherein the determining comprises:

translating a plurality of alignment targets across a field of view of the array;

capturing, by the array during the translating, a plurality of thermal images each associated with at least one of the alignment targets;

detecting, by the temperature sensor during the translating, a plurality of temperature values each associated with at least one of the thermal images; and

processing the thermal images and the temperature values to determine the alignment of the temperature sensor relative to the array.

8. The method of claim 7, wherein the processing comprises:

selecting a first one of the thermal images associated with a first peak temperature value of a first one of the alignment targets;

selecting a second one of the thermal images associated with a second peak temperature value of a second one of the alignment targets; and

comparing the first and second thermal images to determine an intersection between the first and second alignment targets.

9. The method of claim 8, wherein:

the first and second alignment targets comprise heated portions arranged in corresponding first and second patterns; and

the intersection comprises an intersection between the first and second patterns in the first and second images.

10. The method of claim 1, wherein the infrared sensors are microbolometers, the temperature sensor is a pyrometer, and the subset of pixel values is a single pixel value.

11. A system comprising:

an array of infrared sensors configured to capture a thermal image of a scene, wherein the thermal image comprises a plurality of pixel values;

a non-contact temperature sensor configured to detect a temperature value associated with a portion of the scene;

a memory component storing machine-executable instructions; and

a processor configured to execute the instructions to cause the system to;

determine an alignment of the temperature sensor relative to the array,

identify a correspondence between the portion of the scene and a subset of the pixel values based on the alignment of the temperature sensor relative to the array,

compare the subset of pixel values with the detected temperature value,

generate a correction term based on the comparing, and

apply the correction term to at least the subset of pixel values to radiometrically calibrate the subset of pixel values.

12. The system of claim 11, wherein the processor is configured to execute the instructions to cause the system to apply the correction term to all of the pixel values of the thermal image to radiometrically calibrate all of the pixel values.

13. The system of claim 11, wherein the correction term is at least one of an offset correction term and/or a gain correction term.

14. The system of claim 11, wherein the processor is configured to execute the instructions to cause the system to generate a plurality of correction terms associated with different temperatures in response to a plurality of thermal images captured by the array and a plurality of temperature values detected by the temperature sensor.

15. The system of claim 11, wherein the correspondence is based on a distance from the imaging system to the portion of the scene and the alignment of the temperature sensor relative to the array.

16. The system of claim 11, wherein:

the array is configured to capture a plurality of thermal images each associated with at least one of a plurality of alignment targets translated across a field of view of the array;

the temperature sensor is configured to detect a plurality of temperature values each associated with at least one of the thermal images; and

the processor is configured to execute the instructions to cause the system to process the thermal images and the temperature values to determine the alignment of the temperature sensor relative to the array.

17. The system of claim 16, wherein the processor is configured to execute the instructions to cause the system to:

select a first one of the thermal images associated with a first peak temperature value of a first one of the alignment targets;

select a second one of the thermal images associated with a second peak temperature value of a second one of the alignment targets; and

compare the first and second thermal images to determine an intersection between the first and second alignment targets to determine the alignment of the temperature sensor relative to the array.

18. The system of claim 17, wherein:

the first and second alignment targets comprise heated portions arranged in corresponding first and second patterns; and

the intersection comprises an intersection between the first and second patterns in the first and second images.

19. The system of claim 11, wherein the infrared sensors are microbolometers, the temperature sensor is a pyrometer, and the subset of pixel values is a single pixel value.

20. The system of claim 11, wherein the system is a portable thermal imaging camera.