WO2022023748A1

WO2022023748A1 - A thermal imaging system and method

Info

Publication number: WO2022023748A1
Application number: PCT/GB2021/051952
Authority: WO
Inventors: Carrie IAIN; Maguire RICHARD; Osborne DOUGLAS; Shanks JAMIE; Gardner KYLE; Mitchison NAOMI
Original assignee: Thales Holdings Uk Plc
Priority date: 2020-07-31
Filing date: 2021-07-28
Publication date: 2022-02-03
Also published as: GB2597924A; GB202011944D0

Abstract

A system comprising: a thermal imaging camera for detecting thermal radiation from a scene; a first calibration element and a second calibration element, wherein the first and the second calibration elements are coupled with the thermal imaging camera so as to be located or locatable in a field of view of the thermal imaging camera and configurable to be at different temperatures, in use, and at least one measuring device configured to measure the different temperatures of the first and the second calibration elements for calibrating the thermal imaging camera based on the different temperatures of the first and the second calibration elements measured by the measuring device and corresponding thermal imaging of the first and second calibration elements by the thermal imaging camera.

Description

A Thermal Imaging System And Method

FIELD

[0001] The present invention relates to a thermal imaging system and method. More particularly, the method is for calibrating a thermal imaging camera.

BACKGROUND

[0002] A thermal imaging camera is a device that creates an image using infrared (IR) radiation, similar to a common camera that forms an image using visible light. Instead of the 400-700 nanometre range of the visible light camera, infrared cameras are sensitive to wavelengths from about 1,000 nm (1 pm) to about 14,000 nm (14 pm). Infrared imaging systems convert the energy transmitted in the infrared spectrum into a visible light image. Thermal imaging cameras observe and measure IR emission from a scene, thus providing a measure of temperature without being in contact with the source. Thus, thermal imaging cameras provide temperature images of the scene. [0003] Some thermal imaging cameras simply distinguish between the hot and cold regions of a scene, in relative terms. Typically, these types of cameras output a black and white or monochrome image e.g. for surveillance applications. Another type of thermal imaging camera is temperature calibrated, and may be used to provide absolute temperature measurements of the scene.

[0004] The thermal imaging cameras providing absolute temperature measurements need to be calibrated in order for accurate temperatures to be measured by the camera. There may be an initial calibration of the thermal imaging camera but also calibration throughout its lifetime as thermal camera sensitivity may drift over time.

[0005] Previously, calibration may be performed using a black body source located in a scene or an internally heated shutter of the camera. Black bodies are physical bodies with very high emissivity, meaning they radiate and absorb almost all electromagnetic radiation (the theoretical ideal blackbody has an emissivity of 1.0 and perfectly absorbs and emits all radiation).

[0006] It is desirable to provide a thermal imaging system that overcomes or mitigates one or more of the problems of prior thermal imaging camera calibration systems. SUMMARY

[0007] In accordance with a first aspect of the present invention, there is provided a system comprising: a thermal imaging camera for detecting thermal radiation from a scene; a first calibration element and a second calibration element, wherein the first and the second calibration elements are coupled with the thermal imaging camera so as to be located or locatable in a field of view of the thermal imaging camera and configurable to be at different temperatures, in use, and at least one measuring device configured to measure the different temperatures of the first and the second calibration elements for calibrating the thermal imaging camera based on the different temperatures of the first and the second calibration elements measured by the measuring device and corresponding thermal imaging of the first and second calibration elements by the thermal imaging camera.

[0008] The thermal imaging system may provide improved calibration. An advantage may be that the use of costly internal camera components and/or expensive and remote calibration sources may be avoided. The thermal imaging system may be less complex and less expensive than other existing alternatives. The thermal imaging system may remove the need for multiple expensive black body sources to be purchased for large scale rollouts.

[0009] The first and second calibration elements may be emissive in at least part of the electromagnetic spectrum corresponding to the thermal radiation being detected, at least in use.

[00010] The system may be used in reporting of absolute scene temperature.

[00011] The field of view may be a solid angle through which the thermal imaging camera is sensitive to the electromagnetic radiation.

[00012] The first and the second calibration elements may only partially cover the whole field of view.

[00013] At least part of the first and the second calibration elements may be located or locatable in the field of view of the thermal imaging camera, in use.

[00014] All of the first calibration element and/or all of the second calibration element may be located or locatable in the field of view of the thermal imaging camera, in use.

[00015] The first and the second calibration elements may be coupled with the thermal imaging camera so as to continuously remain located or locatable in the field of view of the thermal imaging camera, in use. [00016] The system may comprise a heating source and/or a cooling source configured to respectively heat and/or cool the first calibration element and/or the second calibration element such that the temperature of the second calibration element is substantially higher or lower than the temperature of the first calibration element. [00017] The heating source and/or the cooling source may be electronic.

[00018] The first and/or the second calibration elements may comprise the heating source and/or the cooling source.

[00019] There may be a single heating source. There may be a single cooling source. There may be a plurality of heating sources. There may be a plurality of cooling sources.

[00020] The first calibration element may be heated and/or cooled. The second calibration element may be heated and/or cooled.

[00021] One of the first or second calibration elements may be cooled and the other of the first or second calibration elements may be heated.

[00022] One of the first or second calibration elements may be heated or cooled and the other of the first or second calibration elements may be not heated and not cooled. [00023] The heating and/or cooling of the first and/or second calibration elements may be simultaneous, overlapping or happen at different times.

[00024] The temperature of the first calibration element may be ambient temperature and the heating source and/or the cooling source may be configured to respectively heat and/or cool the second calibration element such that the temperature of the second calibration element is substantially higher or lower than the ambient temperature.

[00025] The first and the second calibration elements may be a distance or distances from the thermal imaging camera such that they are located or locatable in the field of view of the thermal imaging camera.

[00026] The distance or distances may be such that the first and the second calibration elements are close enough to the thermal imaging camera such that they are located or locatable in the field of view of the thermal imaging camera.

[00027] The first and the second calibration elements may be in close proximity to the thermal imaging camera.

[00028] The first and the second calibration elements may be in the same location as the thermal imaging camera.

[00029] The first and the second calibration elements may be substantially the same distance away from the thermal imaging camera. [00030] The first and the second calibration elements may be connected to the thermal imaging camera.

[00031] The first and the second calibration elements may be connected to each other.

[00032] The first and the second calibration elements may be separated by a gap and/or a thermal insulating material.

[00033] The system may comprise a mounting element, wherein the first and second calibration elements may be mounted to the mounting element, and the mounting element may be connected to the thermal imaging camera.

[00034] The first and/or the second calibration elements may be highly emissive in at least part of the electromagnetic spectrum corresponding to the thermal radiation being detected.

[00035] The first and/or the second calibration elements may comprise a body and an emissive surface at least partially covering the body.

[00036] The emissive surface may fully cover the body of the first and/or the second calibration elements.

[00037] The emissive surface may be highly emissive.

[00038] The emissive surface may comprise paint, a coating or finish.

[00039] The paint may be Nextel or Vantablack

[00040] The body of the first and/or the second calibration elements may comprise the heating/and or the cooling source.

[00041] The emissive surface (e.g. the paint) may at least partially cover or fully cover the heating and/or the cooling source.

[00042] The emissive surface (e.g. the paint, coating or finish) may be applied directly onto the heating and/or the cooling source.

[00043] The body of the first and/or the second calibration elements may have a high thermal conductivity.

[00044] The body of the first and/or the second calibration elements may comprise a plate.

[00045] The body of the first and/or the second calibration elements may comprise metal.

[00046] The body of the first and/or the second calibration elements may comprise ceramic.

[00047] The measuring device may be in contact with the first and/or the second calibration elements. [00048] The measuring device may be an electronic measuring device.

[00049] The measuring device may be a thermometer.

[00050] Measurements measured by the measuring device may be sent from the measuring device for processing.

[00051] The thermal imaging camera may be configured to detect the corresponding thermal radiation from the first and the second calibration elements for calibrating the thermal imaging camera substantially simultaneously with detecting thermal radiation detected from the scene for producing a thermal image of the scene.

[00052] The system may further comprise a processor configured to calibrate the thermal imaging camera based upon the different temperatures of the first and the second calibration elements and the corresponding thermal radiation detected from the first and the second calibration elements.

[00053] The processor may be configured to calibrate the thermal imaging camera substantially simultaneously with processing thermal radiation detected from the scene for producing a thermal image of the scene.

[00054] The calibration of the thermal image of the scene may be carried out in real time.

[00055] In accordance with a second aspect of the present invention, there is provided a system comprising: a first calibration element and a second calibration element located or locatable in a field of view of a thermal imaging camera for detecting thermal radiation from a scene, the first and the second calibration elements being configurable to be at different temperatures, in use, and at least one measuring device configured to measure the different temperatures of the first and the second calibration elements for calibrating the thermal imaging camera based on the different temperatures of the first and the second calibration elements measured by the measuring device and corresponding thermal imaging of the first and second calibration elements by the thermal imaging camera; wherein the first and the second calibration elements are configured to be coupled with the thermal imaging camera so as to be located or locatable in the field of view of the thermal imaging camera, in use. [00056] In accordance with a third aspect of the present invention, there is provided a method comprising: detecting thermal radiation from a scene using a thermal imaging camera; measuring, using a measuring device, temperatures of a first calibration element and a second calibration element coupled to the thermal imaging camera such that the first and the second calibration elements are located or locatable in a field of view of the thermal imaging camera whilst the first and the second calibration elements are at different temperatures, for calibrating the thermal imaging camera based on the different temperatures of the first and the second calibration elements measured by the measuring device and corresponding thermal imaging of the first and second calibration elements by the thermal imaging camera.

[00057] The method may further comprise coupling the first and the second calibration elements to the thermal imaging camera such that the first and the second calibration elements continuously remain located or locatable in the field of view of the thermal imaging camera, in use.

[00058] The method may further comprise detecting, with the thermal imaging camera, the corresponding thermal radiation from the first and the second calibration elements for calibrating the thermal imaging camera substantially simultaneously with detecting thermal radiation detected from the scene for producing a thermal image of the scene.

[00059] The method may further comprise calibrating, using a processor, the thermal imaging camera based upon the different temperatures of the first and the second calibration elements and the corresponding thermal radiation detected from the first and the second calibration elements.

[00060] The method may further comprise using the processor, calibrating the thermal imaging camera substantially simultaneously with processing thermal radiation detected from the scene for producing a thermal image of the scene.

[00061] In accordance with a fourth aspect of the present invention, there is provided a method of assembling a system for thermal imaging comprising: providing a thermal imaging camera for detecting thermal radiation from a scene; coupling a first calibration element and a second calibration element with the thermal imaging camera so as to be located or locatable in a field of view of the thermal imaging camera and configurable to be at different temperatures, in use, and arranging at least one measuring device to measure the different temperatures of the first and the second calibration elements for calibrating the thermal imaging camera based on the different temperatures of the first and the second calibration elements measured by the measuring device and corresponding thermal imaging of the first and second calibration elements by the thermal imaging camera.

[00062] In accordance with a fifth aspect of the present invention, there is provided a computer program comprising computer readable instructions configured to cause a processor to carry out a method as described above. [00063] In accordance with a sixth aspect of the present invention, there is provided a computer readable medium carrying a computer program as described above.

[00064] In accordance with a seventh aspect of the present invention, there is provided a computer system for operating a system comprising: a memory storing processor readable instructions; and a processor arranged to read and execute instructions stored in said memory; wherein said processor readable instructions comprise instructions arranged to control the computer to carry out a method as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[00065] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

Figure 1 depicts a target in a scene being imaged by the thermal imaging camera of a thermal imaging system in accordance with an embodiment of the invention;

Figure 2 depicts a plan view of the thermal imaging system in accordance with an embodiment of the invention;

Figure 3 depicts a thermal image taken by the thermal imaging camera of the thermal imaging system in accordance with an embodiment of the invention;

Figure 4 depicts a flow chart of steps in calibrating a thermal imaging camera in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

[00066] Figure 1 shows a system 100 for calibrating a thermal imaging camera 102. The system 100 includes the thermal imaging camera 102. The thermal imaging camera 102 is arranged to detect electromagnetic radiation 104 from a scene. The electromagnetic radiation may be infrared (IR) radiation. That is, radiation having wavelengths from about 1,000 nm (1 pm) to about 14,000 nm (14 pm). The scene may include a target 106 that is being imaged by the thermal imaging camera 102. That is, IR radiation 104 may be being emitted from the target 106 and being detected by the camera 102.

[00067] The thermal imaging camera 102 includes a camera body 108 (or camera housing) and a camera lens 110. The camera 102 has a field of view (defined by dashed lines 112) which may be a solid angle through which the camera 102 is sensitive to the IR radiation. The target 106 in the scene may be located within the field of view. There may be more than one target located in the scene. In general, the camera 102 receives the infrared energy emitted from all of the targets (i.e. bodies) within its field of view. The camera 102 comprises an IR sensor, such as a CMOS sensor, a CCD sensor or the like, which detects the incident infrared energy and converts it into electrical signals which are passed to a processor 115. The processor 115 may process the electrical signals and produce a thermal image of the scene. The processor 115 may be located within the camera body 108 as shown or may be external to and/or separate from the camera 102.

[00068] The thermal imaging system 100 includes a first calibration element 114 and a second calibration element 116 located or locatable in the field of view of the camera 102. More particularly, at least part of the first calibration element 114 and the second calibration element 116 are located or locatable within the field of view of the camera 102, in use. In other embodiments, all of the first calibration element and the second calibration element may be located or locatable in the field of view of the camera, in use.

[00069] The first calibration element 114 and the second calibration element 116 may be emissive in at least part of the electromagnetic spectrum corresponding to the radiation being detected (e.g. infrared radiation) at least in use. The first calibration element 114 and the second calibration element 116 may be highly emissive in the infrared spectrum, at least in use. Highly emissive may be considered to be having an emissivity of approximately equal to, or greater than, 0.95. The spectrum may be mid wavelength infrared (MWIR) and/or long-wavelength infrared (LWIR) depending on the application.

[00070] The thermal imaging system 100 includes a mounting element 118. The mounting element 118 is connected to the thermal imaging camera 102. More particularly, the mounting element is connected to the camera body 108. The first calibration element 114 and the second calibration element 116 are mounted to the mounting element 118.

[00071] Figure 2 shows a plan view of the thermal imaging system 100. The mounting element 118 may comprise a mounting body 120 extending outwardly from the front of the camera 102 (i.e. the part of the camera 102 with the lens 110 facing towards the scene). The mounting element 118 may comprise a mounting arm 122 connected to the mounting body 120 and extending perpendicularly with respect to the mounting body 120. [00072] The first calibration element 114 and the second calibration element 116 may be mounted to the mounting arm 122. In this way, the first calibration element 114 and the second calibration element 116 are connected to each other through the mounting arm 122. In a similar way, the first calibration element 114 and the second calibration element 116 are connected to the camera 102 through the mounting element 118. The first calibration element 114 and the second calibration element 116 may be mounted on either side of the mounting body 120. The first calibration element 114 and the second calibration element 116 may be separated by a gap g. The first calibration element 114 and the second calibration element 116 are mounted to the mounting arm 122 in a position such that they are at least partially in the field of the view of the camera 102.

[00073] The first calibration element 114 and the second calibration element 116 being mounted to the mounting element 118, and the mounting element 118 being connected to the camera body 108 means that the first calibration element 114 and the second calibration element 116 are located in a field of view of the thermal imaging camera 102 in use. The first calibration element 114 and the second calibration element 116 are coupled with the camera 102 so as to be located or locatable in the field of view of the camera 102, in use. It will be appreciated that, in other embodiments, the first and second calibration elements may be mounted in a different way but still be visible in the field of view of the thermal imaging camera. For example, the first and second calibration elements could be mounted within the camera body in a location in front of the lens or at least in front of an IR imaging sensor of the camera, which may provide a more robust configuration. In addition, the first and second calibration elements may be mounted in any way such that they are connected to the camera or a camera housing.

[00074] The thermal imaging system 100 is non interrupting, i.e. the calibration elements 114, 116 do not interrupt the scene (i.e. the viewing of the whole scene) and thus the camera 102 can continue to image while the calibration is being carried out. For example, the first and second calibration elements could be mounted to the camera so that they are provided at the edge / periphery of the field of view of the camera, and optionally coupled so that they always remain at the edge / periphery of the field of view, even as the camera moves. This may facilitate continuous or repeated calibration with minimal interference to the thermal imaging.

[00075] The first calibration element 114 and the second calibration element 116 may be coupled with the camera 102 so as to remain (e.g. continuously or permanently remain) located or locatable in the field of view of the thermal imaging camera, in use. That is, when the camera 102 (and thus the camera body 108) moves (e.g. rotates, pans, tilts, side to side, back and forward, upwards and downwards etc), the first calibration element 114 and the second calibration element 116 may move correspondingly such that they are maintained (e.g. continuously or permanently) in the field of view of the thermal imaging camera 102 (e.g. at all times). The first calibration element 114 and the second calibration element 116 may move with the camera 102 so that they are always in the field of view. This may also facilitate continuous or repeated calibration. However, optionally, the first calibration element 114 and the second calibration element 116 may be mounted so as to be static or fixed on the camera, i.e. although they move with the camera, they do not move within the camera, in contrast to a shutter based system, for example. This may result in a simpler, more robust system, and/or may provide for more stable temperatures of the calibration elements 114, 116 and thereby improve calibration.

[00076] The first calibration element 114 and the second calibration element 116 are located in front of the lens 110 of the camera 102 but they may only partially cover the whole field of view. That is, they only cover part of the field of view and do not block the whole view of the camera 102. However, the distance between the first calibration element 114 and the camera 102 and the distance between the second calibration element 116 and the camera 102 is such that the first calibration element 114 and the second calibration element 116 are continuously located in the field of view of the camera 102. In this embodiment, the first calibration element 114 and the second calibration element 116 are substantially the same distance away from the camera 102 (i.e. the camera lens 110). However, in other embodiments, the first calibration element and the second calibration element may be different distances from the camera.

[00077] The distance or distances may be such that the first calibration element 114 and the second calibration element 116 are close enough to the camera 102 such that they are continuously located in the field of view of the camera 102. That is, the first calibration element 114 and the second calibration element 116 may be in close proximity to the camera 102, i.e. at close range. Thus, the thermal imaging system 100 is kept small and compact. The first calibration element 114 and the second calibration element 116 may be said to be in the same location as the camera 102. Thus, the thermal imaging system 100 can be deployed in one location as the calibration elements 114, 116 attached to the camera 102, not at a distance. [00078] It will be appreciated that, in other embodiments, the first calibration element and the second calibration element may be coupled to the camera in other ways. For example, the first calibration element and the second calibration element may not be physically connected to the camera (e.g. through a mounting element). For example, they could be mounted on one or more other components separate to the camera but which still move correspondingly with the camera such that the first calibration element and the second calibration element are located or locatable (e.g. continuously maintained) in a field of view of the camera. In addition, the first calibration element and the second calibration element may be in different locations or may be mounted to different components.

[00079] Although the description generally describes features for both the first calibration element and the second calibration element, it will be appreciated that, in some embodiments, the first calibration element may include a specified feature and the second calibration element may not, and vice versa, as applicable.

[00080] In an embodiment, the first calibration element 114 and the second calibration element 116 comprise a body and an emissive surface at least partially covering the body. The emissive surface may fully cover the body of the first calibration element 114 and/or the second calibration element 116. The emissive surface is highly emissive. The emissive surface comprises paint. That is, the body is painted with a highly emissive substance. The paint may be Nextel or Vantablack. [00081] The body of the first calibration element 114 and/or the second calibration element 116 comprises a metal plate. The body of the first calibration element 114 and/or the second calibration element 116 has a high thermal conductivity. High thermal conductivity may be considered to be approximately equal to, or greater than, 180 W/mK. In other embodiments, the first calibration element and/or the second calibration element may comprise a different material, such as ceramic (e.g. they may comprise a ceramic plate).

[00082] Referring to Figure 2, the thermal imaging system 100 comprises a first measuring device 124 for measuring the temperature of the first calibration element 114 and a second measuring device 126 for measuring the temperature of the second calibration element 116. The first measuring device 124 is attached to the first calibration element 114 and the second measuring device 124 is attached to the second calibration element 116. Thus, the first and second measuring devices 124,126 are in contact with the first and second calibration elements 114, 116 respectively. [00083] The first and the second measuring devices 124, 126 may accurately measure the temperature of the first and second calibration elements 114, 116 respectively. In other embodiments, there may be one measuring device, e.g. one measuring device for both the first and the second calibration elements, or more than two measuring devices. In other embodiments, the measuring device or devices may not be in contact with and/or not attached to the first calibration element and/or the second calibration element. That is, the temperature may be measured at a distance. In embodiments, the measuring device or devices may be different temperature measuring devices (e.g. thermistors, thermocouples, thermopiles, small remote thermometers, or the like).

[00084] The measuring devices 124, 126 may be electronic or electrical temperature measuring devices. In other embodiments, the measuring devices may be non electronic, e.g. optical fibers with at least one Fabry-Perot or Bragg grating or other temperature sensitive optical feature. Measurements of the temperatures measured by the measuring devices 124, 126 may be sent from the measuring devices 124, 126 for processing. The measurements may be sent to the processor 115 of the camera 102. The measurements may be processed by the processor 115. The temperatures may be reported to wider systems using electronics, which could optionally comprise sending the measurements over a network to a remote processing system.

[00085] The first calibration element 114 and the second calibration element 116 are configurable to be at different temperatures. That is, the first calibration element 114 may have a first temperature and the second calibration element 116 may have a second temperature. Thus, the thermal imaging system 100 provides two different simultaneous temperatures. The first temperature may be ambient (e.g. room) temperature. The ambient temperature measurement may improve calibration and assessment of environmental conditions. The first calibration element 114 may be considered to be an ambient temperature plate.

[00086] The thermal imaging system 100 includes a heating source 128 configured to heat the second calibration element 116 such that the second temperature is substantially higher than the first temperature (i.e. different from the ambient temperature). As an example, the second temperature may be only 1 degree C higher than the first temperature. As a further example, the second temperature may be in a range of 2-5 degrees C higher than the first temperature. The heating source 128 may be sufficiently coupled to the second calibration element 116, e.g. attached to the second calibration element 116, in order to be able to heat the second calibration element 116. The heating source 128 may be electronic.

[00087] The second calibration element 116 may be considered to be heated roughly but measured accurately as it may not be important how high the second temperature is (as long as it is different from the first temperature), rather it is important that it is known accurately. The second calibration element 116 may be considered to be a heated plate. In embodiments, the heating of the second calibration element may be done by a resister based circuit. In other embodiments, the heating source may instead be a cooling source configured to cool the second calibration element 116 such that the second temperature is substantially lower than the first temperature (i.e. different from the ambient temperature). The cooling source may be electronic, such as a Peltier cooling element. In embodiments, there may be a heating source and a cooling source provided to provide a larger temperature range. In embodiments, the second calibration element may comprise the heating source and/or the cooling source.

[00088] It will be appreciated that, in embodiments, the first calibration element may be heated and/or cooled, and/or the second calibration element may be heated and/or cooled. For example, in some cases, both the first calibration element and the second calibration element may be heated (e.g. to different temperatures). In embodiments, the temperature of the first calibration element may not be at the ambient temperature. In general, the heating or cooling may be simultaneous, overlapping or happen at different times. In embodiments, one of the first or second calibration elements may be cooled and the other of the first or second calibration elements may be heated. For example, the first calibration element may be cooled and the second calibration element may be heated. In embodiments, one of the first or second calibration elements may be heated or cooled and the other of the first or second calibration elements may be not heated and not cooled. For example, the second calibration element may be cooled and the first calibration element may be not heated and not cooled.

[00089] In embodiments, the first and/or the second calibration sources may comprise one or more heating and/or cooling sources. That is, one or more of the heating and/or cooling sources may form the body of the first and/or the second calibration sources. In embodiments, the emissive paint may be applied directly to one or more heating and/or the cooling sources. [00090] In embodiments, there may be a plurality of heating and/or cooling sources. For example, one heating source may heat the first calibration element and another heating source may heat the second calibration source. In other embodiments, a single heating source may heat both the first and the second calibration sources. [00091] The first measuring device 124 is configured to measure the first temperature of the first calibration element 114 and the second measuring device 126 is configured to measure the different second temperature of the second calibration element 116. The measuring devices 124, 126 may be relatively sensitive so as to obtain accurate measurements. The temperatures are used to accurately calibrate the thermal imaging camera 102 for thermo-graphic use (reporting of absolute scene temperature). In other embodiments, with only one measuring device, the measuring device is configured to measure the different temperatures of the first and the second calibration elements.

[00092] The first calibration element 114 and the second calibration element 116 are separated by the gap g to reduce or avoid the heating of the first calibration element 114 by the second calibration element 116. In other embodiments, there may be a thermally insulating material between the calibration elements to reduce or avoid the heating of the first calibration element by the second calibration element.

[00093] By providing the thermal imaging system 100 with a known temperature reference point, the data supplied by the thermal imaging camera 102 may be calibrated. The thermal imaging system 100 may be used in reporting of absolute scene temperature. Having two known temperature reference points in the field of view, i.e. the first temperature of the first calibration element 114 and the different second temperature of the second calibration element 116 increases the accuracy of the calibration. This makes it possible to produce accurate temperature measurements, whilst the thermal imaging system 100 remains inexpensive and straightforward to use.

[00094] The processor 115 is configured to calibrate the thermal imaging camera 102 based upon the different temperatures of the first and the second calibration elements 114, 116 and the corresponding thermal radiation detected from the first and the second calibration elements 114, 116. For example, the processor 115 can receive the measurements of the temperatures of the first and the second calibration elements 114, 116 from the measuring devices 124, 126 and the corresponding pixel values for the first and the second calibration elements 114, 116 from the IR sensor of the camera 102 and adjust or determine a relation between the pixel values and temperatures based thereon. The thermal imaging camera 102 is calibrated by determining the response of the camera 102 to known input irradiance from the first and the second calibration elements 114, 116. Since the temperatures of both the first and the second calibration elements 114, 116 is known, the response of the camera 102 can be accurately computed at any time t and thus applied to the whole scene to determine temperature or temperatures (e.g. of a target 106) in the image.

[00095] The processor 115 may be configured to calibrate the thermal imaging camera 102 substantially simultaneously with processing radiation detected from the scene for producing a thermal image of the scene. The thermal imaging system 100 may calibrate every image seen by the camera 102.

[00096] Figure 3 shows a thermal image 130 taken by the thermal imaging camera 102. The image 130 shows the target 106 (i.e. a person’s head and upper torso) and the first calibration element 114 (the ambient temperature plate) and the second calibration element 116 (the heated plate). It can be seen that the ambient temperature plate and the heated plate is visible to the camera 102 and are very close to the camera 102. For example, the ambient temperature plate (first calibration element 114) and/or the heated plate (second calibration element 116) may be a distance or distances in a range of 5-10cm away from the camera 102 (e.g. the lens 110 of the camera 102. The ambient temperature plate and the heated plate may be always visible to the camera 102. The ambient temperature plate (first calibration element 114) and/or the heated plate (second calibration element 116) may be in focus or out of focus. The ambient temperature plate is a similar shade to the clothes of the person (target 106) and the background, and thus a similar temperature, and the heated plate is a similar shade to the exposed skin of the person (target 106), and thus a similar temperature. Heating the second calibration element 116 to a temperature that is the same as, or relatively close to, the temperature of the target 106 may provide improved calibration. The temperature of the target 106 may be bracketed in this way, but it is not necessary to do this for the calibration. The thermal image 130 may be used in calibrating the thermal imaging camera 102, in combination with the temperature measurements of the ambient temperature plate and the heated plate such that an accurate temperature of the person (target 106) may be provided. This may be useful to determine if, e.g. the person has a fever.

[00097] The thermal imaging camera 102 is configured to detect the corresponding thermal radiation from the first and the second calibration elements 114, 116 for calibrating the thermal imaging camera 102 substantially simultaneously with detecting thermal radiation 104 detected from the scene for producing the thermal image 130 of the scene. The thermal radiation 104 detected from the scene for producing the thermal image 130 may include the thermal radiation from the target 106 (the person). The calibration of the camera 102 may be carried out in real time, i.e. a live calibration. [00098] The first and the second calibration elements 114, 116 being continuously in the field of view of the thermal imaging camera 102 provides two constant data points (rather than only one) for calibration. This may lead to more accurate and more precise thermo-graphic calibration. The calibration of the camera 102 may be carried out constantly in real time, i.e. a live constant calibration.

[00099] The first and second calibration elements 114, 116 being coupled with the camera 102 so as to be located or locatable in the field of view of the camera 102, in use, removes the need for a shutter or remote black body source for calibration. Previous systems may rely on either an expensive Black Body calibration source to be permanently in the scene or an internally heated shutter.

[000100] The previous black body solution is significantly more expensive than the thermal imaging system 100 of the present invention [e.g. one to two orders of magnitude]. The black body source only provides one calibration temperature. The black body sources are required to be in the image so, if there are a large number of systems, then a correspondingly large number of expensive black body sources may be needed. This is not only expensive but means the overall system is spread over a larger area to ensure the cameras can see the targets (subjects) and the black body source simultaneously as the black body source and camera need to be separated by some distance. These black body sources are placed in the scene at some distance from the cameras, with no feed back into the wider system of calibration source temperature drift. This means the overall system (camera and black body source) has to be spread over two locations taking up more space. The solution of the present invention using the calibration elements 114, 116 is also smaller (more compact) than black body source calibration options.

[000101] The thermal imaging system 100 of the present invention may be connected to the camera 102 so may only require one location. This makes it easier to fit into tighter spaces and scale up to multiple stations in, for example, an airport, railway station or office entry turnstiles.

[000102] Previous shutters may be slid in front of a camera periodically. These (internal) shutters add significant complexity to a camera design, only provide one calibration temperature and are significantly harder to retrofit to existing cameras and systems. The shutters are also not always in the scene and therefore less quick to respond to camera drift. Shuttered systems interrupt the scene and mean the camera cannot continue to image while the shutter is across. In addition, these shuttered systems do not provide information about ambient temperature which may be useful for camera calibration.

[000103] Advantages of the thermal imaging system 100 of the present invention include avoiding costly internal camera components and/or expensive and remote calibration sources that may be less practical in certain scenarios such as in airports or mass transit systems. Furthermore, the thermal imaging system 100 provides two different calibration temperatures, instead of only one calibration temperature, which may result in an improvement to the calibration. The thermal imaging system 100 removes the need for multiple expensive black body sources to be purchased for large scale rollouts (for example in an airport fever screening system or border patrol system).

[000104] The calibration elements 114, 116, as well as the target whose temperature is to be measured, being in the field of view of the thermal imaging camera 102 means that calibration and temperature measurement may effectively be carried out simultaneously. This removes the need for an advance calibration sequence and so makes the thermal imaging system 100 easy to use and versatile.

[000105] The thermal imaging system 100 may be used in many different applications such as, mass transit screening and monitoring, public space monitoring, office entry screening, medical triage, thermal cameras, thermal camera calibration, temperature screening (e.g. mass transit systems and public places) and camera calibration in manufacturing.

[000106] The thermal imaging system 100 helps solve the problem of thermal camera sensitivity drifting over time. It allows there to be objects (i.e. the calibration elements 114, 116) of known temperature to be visible by the camera 102 allowing a live calibration and allows for accurate temperatures to be measured by the camera 102. In many cases, the calibration for the scene may be 5-1 Ox more accurate.

[000107] Further advantages of the thermal imaging system 100 include it being less complex and expensive than other existing alternatives [e.g. at least one to two orders of magnitude]. The calibration elements 114, 116 can be connected directly to the camera 102 so no need for remote Black Body source making it significantly more compact. The calibration elements do not need to be driven to a precise temperature unlike other systems. [000108] The components of the thermal imaging system 100 (e.g. the first and second calibration elements, the mounting element 118, the heating source 128 and/or the measuring devices 124, 126) can be retrofitted to existing camera systems (i.e. existing thermal imaging cameras). That is, in embodiments, there may be provided a system (e.g. a retrofit system) comprising a first calibration element and a second calibration element located or locatable in a field of view of a thermal imaging camera for detecting radiation from a scene. The first and the second calibration elements being configurable to be at different temperatures, in use. The system may comprise at least one measuring device configured to measure the different temperatures of the first and the second calibration elements for calibrating the thermal imaging camera based on the different temperatures of the first and the second calibration elements measured by the measuring device and corresponding thermal imaging of the first and second calibration elements by the thermal imaging camera. The first and the second calibration elements of the system are configured to be coupled with the thermal imaging camera so as to be located or locatable in the field of view of the thermal imaging camera, in use. The system may comprise a heating source for heating the second calibration element and/or any of the other features described in the thermal imaging system 100 excluding the thermal imaging camera 102.

[000109] Figure 4 shows a flow chart 200 of steps in calibrating a thermal imaging camera 102 in accordance with an embodiment of the invention.

[000110] Step S201 includes coupling the first calibration element 114 and the second calibration element 116 to the thermal imaging camera 102 such that the first calibration element 114 and the second calibration element 116 are located or locatable in the field of view of the thermal imaging camera 102, in use. The coupling of the first and the second calibration elements 114, 116 to the thermal imaging camera 102 may be such that the first and the second calibration elements 114, 116 continuously remain located or locatable in the field of view of the thermal imaging camera 102, in use.

[000111] In step S202, the second calibration element 116 is heated to the second temperature using the heating source 128. The second temperature is higher than the first temperature (ambient temperature) of the first calibration element 114. The first calibration element 114 and the second calibration element 116 are configurable to be at different temperatures. [000112] In step S203, temperatures of the first calibration element 114 and the second calibration element 116 located or locatable in a field of view of the thermal imaging camera 102 are measured using measuring devices 124, 126.

[000113] In step S204, thermal radiation is detected from the first calibration element 114 and the second calibration element 116 using the thermal imaging camera 102. Thermal radiation 104 may be detected from the scene using the thermal imaging camera 102. The thermal radiation 104 may be from the first calibration element 114, the second calibration element 116, and the target 106 in the field of view of the camera 102.

[000114] In step S205, the processor 115 calibrates the thermal imaging camera 102 based upon the different temperatures of the first calibration element 114 and the second calibration element 116 and the corresponding thermal radiation detected from the first calibration element 114 and the second calibration element 116. The calibration of the thermal imaging camera 102 may be substantially simultaneous with processing the thermal radiation 104 detected from the scene for producing a thermal image 130 of the scene.

[000115] Where the context allows, embodiments of the invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g. carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. and in doing that may cause actuators or other devices to interact with the physical world.

[000116] While certain embodiments have been described, these embodiments have been presented by way of example only and are not intended to limit the scope of the invention. Indeed, the novel methods, devices and systems described herein may be embodied in a variety of forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the scope of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope of the invention.

Claims

CLAIMS:

1. A system comprising: a thermal imaging camera for detecting thermal radiation from a scene; a first calibration element and a second calibration element, wherein the first and the second calibration elements are coupled with the thermal imaging camera so as to be located or locatable in a field of view of the thermal imaging camera and configurable to be at different temperatures, in use, and at least one measuring device configured to measure the different temperatures of the first and the second calibration elements for calibrating the thermal imaging camera based on the different temperatures of the first and the second calibration elements measured by the measuring device and corresponding thermal imaging of the first and second calibration elements by the thermal imaging camera.

2. The system of claim 1, wherein the first and the second calibration elements are coupled with the thermal imaging camera so as to continuously remain located or locatable in the field of view of the thermal imaging camera, in use.

3. The system of either of claims 1 or 2, wherein the system comprises a heating source and/or a cooling source configured to respectively heat and/or cool the first calibration element and/or the second calibration element such that the temperature of the second calibration element is substantially higher or lower than the temperature of the first calibration element.

4. The system of claim 3, wherein the temperature of the first calibration element is ambient temperature and wherein the heating source and/or the cooling source is configured to respectively heat and/or cool the second calibration element such that the temperature of the second calibration element is substantially higher or lower than the ambient temperature.

5. The system of any preceding claim, wherein the first and the second calibration elements are a distance or distances from the thermal imaging camera such that they are located or locatable in the field of view of the thermal imaging camera.

6. The system of claim 5, wherein the first and the second calibration elements are substantially the same distance away from the thermal imaging camera.

7. The system of any preceding claim, wherein the first and the second calibration elements are connected to the thermal imaging camera.

8. The system of claim 7, wherein the first and the second calibration elements are connected to each other.

9. The system of claim 8, wherein the first and the second calibration elements are separated by a gap and/or a thermal insulating material.

10. The system of either of claims 8 or 9, wherein the system comprises a mounting element, wherein the first and second calibration elements are mounted to the mounting element, and the mounting element is connected to the thermal imaging camera.

11. The system of any preceding claim, wherein the first and/or the second calibration elements are highly emissive in at least part of the electromagnetic spectrum corresponding to the thermal radiation being detected.

12. The system of any preceding claim, wherein the first and/or the second calibration elements comprises a body and an emissive surface at least partially covering the body.

13. The system of claim 12, wherein the body of the first and/or the second calibration elements has a high thermal conductivity.

14. The system of any preceding claim, wherein the measuring device is in contact with the first and/or the second calibration elements.

15. The system of any preceding claim, wherein the thermal imaging camera is configured to detect the corresponding thermal radiation from the first and the second calibration elements for calibrating the thermal imaging camera substantially simultaneously with detecting thermal radiation detected from the scene for producing a thermal image of the scene.

16. The system of any preceding claim, further comprising a processor configured to calibrate the thermal imaging camera based upon the different temperatures of the first and the second calibration elements and the corresponding thermal radiation detected from the first and the second calibration elements.

17. The system of claim 16, wherein the processor is configured to calibrate the thermal imaging camera substantially simultaneously with processing thermal radiation detected from the scene for producing a thermal image of the scene.

18. A system comprising: a first calibration element and a second calibration element located or locatable in a field of view of a thermal imaging camera for detecting thermal radiation from a scene, the first and the second calibration elements being configurable to be at different temperatures, in use, and at least one measuring device configured to measure the different temperatures of the first and the second calibration elements for calibrating the thermal imaging camera based on the different temperatures of the first and the second calibration elements measured by the measuring device and corresponding thermal imaging of the first and second calibration elements by the thermal imaging camera; wherein the first and the second calibration elements are configured to be coupled with the thermal imaging camera so as to be located or locatable in the field of view of the thermal imaging camera, in use.

19. A method comprising: detecting thermal radiation from a scene using a thermal imaging camera; measuring, using a measuring device, temperatures of a first calibration element and a second calibration element coupled to the thermal imaging camera such that the first and the second calibration elements are located or locatable in a field of view of the thermal imaging camera whilst the first and the second calibration elements are at different temperatures, for calibrating the thermal imaging camera based on the different temperatures of the first and the second calibration elements measured by the measuring device and corresponding thermal imaging of the first and second calibration elements by the thermal imaging camera.

20. The method of claim 19, further comprising, coupling the first and the second calibration elements to the thermal imaging camera such that the first and the second calibration elements continuously remain located or locatable in the field of view of the thermal imaging camera, in use.

21. The method of either of claims 19 or 20, further comprising, detecting, with the thermal imaging camera, the corresponding thermal radiation from the first and the second calibration elements for calibrating the thermal imaging camera substantially simultaneously with detecting thermal radiation detected from the scene for producing a thermal image of the scene.

22. The method of any of claims 19 to 21, further comprising calibrating, using a processor, the thermal imaging camera based upon the different temperatures of the first and the second calibration elements and the corresponding thermal radiation detected from the first and the second calibration elements.

23. The method of claim 22, further comprising, using the processor, calibrating the thermal imaging camera substantially simultaneously with processing thermal radiation detected from the scene for producing a thermal image of the scene.

24. A method of assembling a system for thermal imaging comprising: providing a thermal imaging camera for detecting thermal radiation from a scene; coupling a first calibration element and a second calibration element with the thermal imaging camera so as to be located or locatable in a field of view of the thermal imaging camera and configurable to be at different temperatures, in use, and arranging at least one measuring device to measure the different temperatures of the first and the second calibration elements for calibrating the thermal imaging camera based on the different temperatures of the first and the second calibration elements measured by the measuring device and corresponding thermal imaging of the first and second calibration elements by the thermal imaging camera.

25. A computer program comprising computer readable instructions configured to cause a processor to carry out a method according to any one of claims 19-23.

26. A computer readable medium carrying a computer program according to claim 24.

27. A computer system for operating a system comprising: a memory storing processor readable instructions; and a processor arranged to read and execute instructions stored in said memory; wherein said processor readable instructions comprise instructions arranged to control the computer to carry out a method according to any one of claims 19 to 23.