Thermal imager with non-uniformity correction

• US 8,760,509 B2
• Filed: 01/21/2011
• Issued: 06/24/2014
• Est. Priority Date: 12/31/2010
• Status: Active Grant

• Current Assignee: Fluke Corporation (Fortive Corp.)
• Original Assignee: Fluke Corporation (Fortive Corp.)
• Inventors: Schmidt, Matthew F., Johnson, Kirk R.
• Primary Examiner(s): Rao, Andy
• Assistant Examiner(s): WALKER, JARED T
• Application Number:
  US13/011,846
• Publication Number:
  US 20120169866A1
• Time in Patent Office: 1,250 Days
• Field of Search: 348/135, 348/164
• US Class Current: 348/135
• CPC Class Codes: H04N 23/11 for generating image signals from visible and infrared light wavelengths
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• CPC Class Codes: H04N 25/677 for reducing the column or line fixed pattern noise
• 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

Infrared cameras are susceptible to fixed-pattern noise artifacts. These artifacts are due to numerous sources and typically show up as non-uniformities in an IR image of a uniform scene. Devices for and methods of refining non-uniformity corrections in an infrared (IR) camera are provided that correct for remaining fixed pattern noise.

Claims

1. A method of correcting for residual fixed pattern noise in a radiometric infrared (IR) camera, the method comprising:

pointing the camera at a first scene external to the camera;

generating sets of IR image data, while pointing the camera at the first scene, said sets of IR image data representative of IR energy received on a focal plane array (FPA) within the camera, the FPA including a plurality of IR detector elements;

initiating a non-uniformity correction (NUC) routine, the NUC routing including;

generating a first set of IR image data representative of the IR energy received on the FPA, and

generating NUC data from the first set of IR image data, the NUC data for correcting fixed pattern noise in the first set of IR image data;

pointing the camera at a second scene external to the camera to produce a scene that effectively is of uniform IR energy;

triggering the camera, while pointing the camera at the second scene, and initiating an NUC refinement routine including;

generating a second set of IR image data representative of IR energy received on the FPA from the second scene,

generating NUC refinement data from the second set of IR image data, and

generating normalized NUC refinement data by normalizing the NUC refinement data relative to IR image data in the second set of IR image data associated with at least one of a generally centrally positioned IR detector element from the plurality of IR detector elements;

generating adjusted NUC data by adjusting the NUC data with the normalized NUC refinement data;

adjusting at least one set of the IR image data with the adjusted NUC data to minimize fixed pattern noise in the at least one set of the IR image data; and

calculating radiometric scene temperature data associated with at least a portion of the first scene based on at least a portion of at least one set of the IR image data, the NUC data, and the normalized NUC refinement data.

2. The method of claim 1, wherein the NUC correction routine includes blocking IR energy from the first scene from reaching the FPA before generating the NUC data.

3. The method of claim 2, wherein the blocking is performed using a shutter located inside the radiometric IR camera.

4. The method of claim 1, wherein the NUC correction routine is performed without the use of a shutter located inside the radiometric IR camera.

5. The method of claim 1, wherein pointing the camera at a second scene external to the camera to produce a scene that effectively is of uniform IR energy includes pointing the camera at a uniform IR energy scene.

6. The method of claim 1, wherein pointing the camera at a second scene external to the camera to produce a scene that effectively is of uniform IR energy includes pointing the camera at an external scene located outside of the focus range of the lens.

7. The method of claim 6, wherein the external scene located outside of the focus range of the lens is located in close proximity to a lens of the radiometric IR camera.

8. The method of claim 1, further comprising validating the normalized NUC refinement data to determine whether it varies too widely.

9. The method of claim 8, wherein the normalized NUC refinement data is rejected if it varies too widely.

10. The method of claim 1, further comprising canceling the NUC refinement by removing the normalized NUC refinement data from the adjusted NUC data.

11. The method of claim 10, wherein the canceling the NUC refinement is occurs based on the amount of time lapsed since the prior NUC refinement, based on a threshold temperature change to some component of the radiometric IR camera, based on a change in position of a lens of the radiometric IR camera, or based on receipt of a manual input.

12. The method of claim 1, wherein the at least one of the generally centrally positioned IR detector elements is only one generally centrally positioned IR detector elements.

13. The method of claim 1, further comprising displaying on a display of the radiometric IR camera an IR image of the first scene as represented by the adjusted at least one set of the IR image data.

14. The method of claim 1, further comprising displaying the radiometric scene temperature data associated with at least a portion of the first scene.

15. A method of tracking temperature profile changes in a scene using an infrared (IR) camera, the method comprising:

pointing the camera at a first scene external to the camera, the first scene being of generally non-uniform IR energy;

generating sets of IR image data, while pointing the camera at the first scene, said sets of IR image data representative of IR energy received from the first scene on a focal plane array (FPA) within the camera, the FPA including a plurality of IR detector elements;

initiating a non-uniformity correction (NUC) routine, the NUC routing including;

generating a first set of IR image data representative of the IR energy received on the FPA from the first scene, and

generating NUC data from the first set of IR image data, the NUC data for correcting fixed pattern noise in the first set of IR image data;

triggering the camera, while pointing the camera at the first scene, and initiating an NUC refinement routine including;

generating a second set of IR image data representative of IR energy received on the FPA from the first scene,

generating NUC refinement data from the second set of IR image data, and

generating normalized NUC refinement data by normalizing the NUC refinement data relative to IR image data in the second set of IR image data associated with at least one of a generally centrally positioned IR detector element from the plurality of IR detector elements;

generating adjusted NUC data by adjusting the NUC data with the normalized NUC refinement data;

adjusting at least one set of the IR image data with the adjusted NUC data to minimize fixed pattern noise in the at least one set of the IR image data;

displaying on a display of the IR camera a generally uniform IR image of the first scene as represented by the adjusted at least one set of the IR image data.

16. The method of claim 15, further comprising analyzing the displayed IR image for changes to the temperature profile in the first scene.

17. A radiometric infrared (IR) camera for correcting for residual fixed pattern noise, comprising:

a housing;

a focal plane array (FPA) mounted within the housing and adapted to receive IR energy, the FPA comprising a plurality of IR detector elements and generating sets of IR image data representing IR energy received on the FPA;

a lens mounted on the housing for directing IR energy from a target scene onto the FPA;

a shutter disposed within the housing, the shutter movable between open and closed positions, the closed position being such that the shutter is positioned between the lens and the FPA to prevent IR energy from the target scene from reaching the FPA, the open position permitting IR energy from the scene to reach the FPA;

a switch supported by the housing, the switch, when triggered, initiating a non-uniformity correction (NUC) refinement routine during which the shutter remains in the open position and a first set of IR image data is generated representing IR energy levels received on the FPA from a scene external to the camera;

a processor operatively coupled to the FPA for receiving and processing the sets of IR image data, the processor for initiating a NUC routine during which the shutter is temporarily moved to the closed position and a second set of IR image data is generated representing IR energy received on the FPA while the shutter is in the closed position, the processor generating offset data from the second set of IR image data, the processor generating NUC refinement data from the first set of IR image data, the processor generating adjusted NUC data by adjusting the NUC data with the NUC refinement data, the adjusted NUC data for use by the camera to provide fixed-pattern noise correction; and

a display supported by the housing and operatively connected to the processor for displaying an adjusted IR image of the target scene based on the adjusted NUC data.