Thermal imaging camera and method for the determination of the lens parameters of an IR interchangeable lens of a thermal imaging camera

• US 8,247,770 B2
• Filed: 03/02/2010
• Issued: 08/21/2012
• Est. Priority Date: 03/02/2010
• Status: Active Grant

• Current Assignee: Testo AG
• Original Assignee: Testo AG
• Inventors: Fischer, Jörn
• Primary Examiner(s): Porta, David
• Assistant Examiner(s): Maupin, Hugh H
• Application Number:
  US12/716,005
• Publication Number:
  US 20110215244A1
• Time in Patent Office: 903 Days
• Field of Search: 250/338.1
• US Class Current: 250/338.1
• CPC Class Codes: G02B 23/12 with means for image conversion or intensification
• CPC Class Codes: H04N 17/002 for television cameras
• 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

In a thermal imaging camera (1) with an IR sensor arrangement (2) and an interchangeable IR lens (5), an image processing unit (12) and a data processing unit (13) are provided with which at least one feature (8, 9) can be extracted from a recorded IR image (6) and a numerical value (14) can be derived from this feature, wherein the numerical value (14) is determined by the distortion of the interchangeable IR lens (5), and a mapping (16) of lens characteristics (17, 18, 19) with the determinable numerical values (14) is stored.

Claims

1. Thermal imaging camera (1) with an IR sensor arrangement (2), an output unit for the processed sensor data and an interchangeable IR lens (5), characterized in that the interchangeable IR lens (5) features distortion, in that an image processing unit (12) is constructed and this image processing unit (12) is designed to extract at least one feature from at least one IR image (6) recorded with IR sensor arrangement (2), wherein the one or more features are influenced by the distortion of interchangeable IR lens (5), and in that a data processing unit (13) is constructed and designed to derive a numerical value (14) that is determined by the distortion of interchangeable IR lens (5) from the one or more extracted features.

2. Thermal imaging camera (1) according to claim 1, characterized in that a mapping (16) of lens characteristics (17, 18, 19) to numerical values (14) that can be determined with data processing unit (13) is stored in a memory unit (15) and/or in that a data readout unit (20) is formed and is designed for reading out stored lens characteristics (17, 18, 19) for the numerical value (14) determined with data processing unit (13).

3. Thermal imaging camera (1) according to claim 2, characterized in that the stored lens characteristics (17, 18, 19) comprise one or more of the following lens characteristics:

focal length, transmission coefficient(s) (19), distortion, or photographic luminous intensity.

4. Thermal imaging camera (1) according to claim 1, characterized in that the one or more extracted features are edges and/or that the numerical value is determined by the preferably averaged radius of curvature of at least one linear structure (7, 8, 9, 27) in IR image (6).

5. Thermal imaging camera (1) according to claim 1, characterized in that image processing unit (12) is set up for evaluating different image areas (25, 26), in particular, at least one peripheral area (25) and at least one central area (26) of one or more recorded IR images (6).

6. Method for determining lens characteristics (17, 18, 19) of an interchangeable IR lens (5) of a thermal imaging camera (1), characterized in that at least one IR image (6) is recorded with interchangeable IR lens (5), in that one or more features are extracted from the one or more IR images (6), with the one or more features being influenced by the distortion of interchangeable IR lens (5), in that a numerical value (14) determined by the distortion of interchangeable IR lens (5) is derived from the one or features, and in that at least one lens characteristic (17, 18, 19) correlated with numerical value (14) is read out from a stored mapping (16) of lens characteristics (17, 18, 19) with numerical values (14).

7. Method according to claim 6, characterized in that at least one extracted feature is an edge (8, 9, 27) and/or that one or more of the following lens characteristics (17, 18, 19) are stored:

focal length, transmission coefficient(s), distortion or photographic luminous intensity.

8. Method according to claim 6, characterized in that at least two recorded IR images (6) are evaluated during the feature extraction, in particular, that a peripheral area (25) is evaluated in a first IR image (6) and in the first or a second IR image (6) a central area (26) is evaluated and/or that at least one radius of curvature of a linear structure (7, 8, 9, 27) is determined in the one or more IR images (6) in order to derive the numerical value (14).

9. Method according to claim 6, characterized in that a vector field is calculated for the one or more IR images (6) by means of a color level or gray level progression and/or in that a vector summed up over a partial area of IR image (6) is calculated.

10. Method according to claim 9, characterized in that, from the summed-up vectors for a sequence of IR images (6), a vector averaged over the sequence is calculated and/or in that object (3) is imaged in a sequence of at least two IR images (6) in different image areas (25, 26), in particular, in a peripheral area (25) and in a central area (26), in that object (3) is identified in the two or more IR images (6), in that at least one respective feature is extracted from the imaged object (3) for each IR image (6), and in that the numerical value (14) is derived from the comparison of the extracted features.

11. Method according to claim 6, characterized in that the movement of object (3) between two successive IR images (6) is determined by calculating the mapping and/or by a motion sensor.

12. Method for processing an IR image (6) recorded with a thermal imaging camera (1), characterized in that at least one lens characteristic (17, 18, 19) is determined in a method according to claim 6, and in that the one or more lens characteristics (17, 18, 19) are used in the processing of the recorded IR image (6).