Method, device, and system for temperature calibration and determination of temperature in scene

Abstract

To provide a method for temperature calibration and determination of temperature in a scene.SOLUTION: A method includes: collecting, at each time point out of a plurality of time points in a first period, an ambient temperature representing the temperature of a first part of a scene and collecting a plurality of thermal image sensor signal values corresponding to the collected ambient temperatures and related to the first part; determining a calibration function based on the collected ambient temperatures and the thermal image sensor signal values corresponding to the collected ambient temperatures; and capturing, in a second period, a thermal image of the scene including thermal image sensor signal values related to a second part of the scene and determining the temperature of the second part of the scene based on the calibration function and based on the thermal image sensor signal values included in the thermal image.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The embodiments described herein relate to the field of thermal cameras. In particular, the embodiments described herein relate to temperature calibration and determination of temperature within a scene.

Background Art

[0002] Sometimes, a thermal camera, also called a thermographic camera, an infrared camera, a thermal imaging camera, or infrared thermography, is an imaging device that forms a heat zone image using infrared radiation, similar to a general camera that forms an image using visible light. Instead of the 380 - 780 nanometers of visible light cameras, thermal cameras operate at wavelengths from about 3 micrometers up to about 14 micrometers.

[0003] Thermal cameras have applications in a wide range of areas, such as, to name a few, object detection, anomaly detection, fire monitoring, trend analysis, etc. In many of these applications, it is important to accurately measure the temperature(s) within the imaged scene. However, today, calibrating a thermal camera to accurately measure temperature is difficult and costly.

[0004] For example, a thermal camera can be calibrated in a manufacturing plant by placing it in a calibration chamber or calibration room with a constant chamber / room temperature. Once the thermal camera has adapted to the constant temperature in the calibration chamber, various objects with clearly defined different absolute temperatures are placed in front of the thermal camera, one at a time, to calibrate it. In particular, each object is placed within the scene covered by the thermal camera's field of view. For the temperature of each object, the thermal camera captures an image of the scene and records the respective image sensor signal value for each sensor element of the image sensor. Once the sensor signal values ​​have been recorded for all the various objects, a configuration function for each sensor element is determined. The calibration function relates absolute temperature to the sensor signal value. The calibration procedure is very time-consuming because multiple objects with clearly defined different temperatures must be placed in the calibration chamber, and because the sensor signal values ​​for each sensor element of the image sensor must be recorded to obtain the calibration function. Sometimes, once the calibration function has been determined for each sensor element of the thermal camera, the thermal camera is said to be fully calibrated.

[0005] U.S. Patent No. 6,267,501 describes another example of factory calibration using a calibration chamber. In this example, a thermal camera is placed inside a calibration chamber at a controlled ambient temperature. The thermal camera faces a scene that is isothermal across the scene through the walls of the calibration chamber, and this temperature is presented to all of the thermal camera's sensor elements. During the calibration of the thermal camera, both the chamber temperature and the scene temperature fluctuate. In particular, for each chamber temperature, the scene temperature fluctuates within a certain temperature interval, and for each scene temperature, the thermal camera records sensor signal values ​​through the window of the calibration chamber. Subsequently, the chamber temperature is changed, and the thermal camera records sensor signal values ​​for each scene temperature within that temperature interval. Once sensor signal values ​​have been recorded for all temperatures, i.e., for all chamber temperatures combined with all scene temperatures, a calibration function for each sensor element and each chamber temperature is determined. The calibration function for each sensor element relates the absolute temperature to the sensor signal value for a thermal camera operating at that chamber temperature. Since the calibration function is determined for each sensor element in this example, the thermal camera is said to be fully calibrated.

[0006] Figure 1A schematically shows exemplary calibration functions for different sensor elements of a thermal camera said to be fully calibrated. The calibration function for the sensor element marked "A" is shown as curve A, the calibration function for the sensor element marked "B" is shown as curve B, and the calibration function for the sensor element marked "C" is shown as curve C. In Figure 1A, each calibration curve is valid for three sensor elements. However, this is merely an example, and it should be understood that each calibration function may be valid for a different number of sensor elements. Figure 1A also shows that calibration is performed over a wide range of temperatures, for example, between 0°C and 300°C.

[0007] Some drawbacks of at least some fully calibrated thermal cameras are that they take time to calibrate, and that they must be recalibrated years later, sometimes even annually. The thermal camera must then be returned to the factory, where one of the aforementioned procedures must be repeated. This is particularly inconvenient for thermal cameras installed in locations far from the factory.

[0008] Figure 1B schematically shows exemplary calibration functions for different sensor elements of a thermal camera said to be standard calibrated. As used in this disclosure, the expression "standard calibrated" means that the same type of thermal camera is calibrated using a single calibration function, sometimes referred to as the default calibration function. As can be seen in Figure 1B, the calibration function is the same for all nine sensor elements.

[0009] One drawback of standard-calibrated thermal cameras is that a single calibration function is used to calibrate thermal cameras of the same type, i.e., thermal cameras with the same type of image sensor. Therefore, variations in the performance of individual sensor elements are not taken into account in the calibration. Another drawback of some standard-calibrated thermal cameras is that they may need to be recalibrated after several years, sometimes even annually. For example, depending on the age of a standard-calibrated thermal camera, the camera may need to be calibrated using a new calibration function that takes into account the camera's aging, i.e., the aging of the image sensor.

[0010] U.S. Patent Application Publication No. 2018 / 0191967 discloses an infrared (IR) imaging system for determining the concentration of a target species within an object. The imaging system may include an optical system comprising an optical focal plane array (FPA) unit. The optical system may have components defining its at least two optical channels, which are spatially and spectrally distinct from each other. Each of the at least two optical channels may be positioned to direct IR radiation incident on the optical system toward the optical FPA. The system may include a processing unit comprising a processor, which may be configured to acquire multispectral optical data indicating the target species from the IR radiation received by the optical FPA. [Overview of the project]

[0011] In consideration of the foregoing, and therefore, the object of the embodiments disclosed herein is to overcome or at least mitigate the drawbacks discussed above. In particular, the object is to provide methods, devices, and systems that provide a simple temperature calibration of a thermal camera and still provide a sufficiently accurate determination of the temperature in a scene.

[0012] The embodiments disclosed herein are applicable for in-situ temperature calibration of thermal cameras. As used in this disclosure, the term "in-situ temperature calibrate" means that the temperature calibration is performed in the same location where the thermal camera is operating or is expected to operate. Therefore, the location can be the same location where the thermal camera is installed when it is operating. In-situ calibration enables on-the-fly calibration of the thermal camera, i.e., calibration of the thermal camera during its normal operation.

[0013] According to one embodiment, the objective is achieved by a method for temperature calibration and determination of the temperature within a scene.

[0014] The method includes collecting ambient temperatures representing the temperature of a first part of a scene at each of several points in time within a first period, in order to obtain collected ambient temperatures over a certain range of ambient temperatures, and collecting one or more thermal image sensor signal values ​​corresponding to the collected ambient temperatures and related to the first part of the scene using a thermal camera.

[0015] The calibration function is determined based on the collected ambient temperature and one or more thermal image sensor signal values ​​corresponding to each of the collected ambient temperatures. The calibration function provides temperature as a function of the thermal image sensor values.

[0016] During the second period, the thermal camera captures a thermal image of the scene, and the thermal camera includes thermal image sensor values ​​related to the second portion of the scene.

[0017] During the second period, the temperature of the second portion of the scene is determined based on a calibration function and on one or more thermal image sensor signal values ​​included in the captured thermal image of the scene and related to the second portion of the scene.

[0018] In such a method, the calibration function is determined based on the collected ambient temperature representing the temperature of the first part of the scene, and one or more thermal image sensor signal values ​​corresponding to each of the collected ambient temperatures. The calibration function can be created, for example, by regression analysis, thereby finding a mathematical function that best fits the collected data. The function can then be created and adjusted to fit the collected values. The scene can be the scene in which the thermal camera is positioned to monitor it when it is operating, and the first part of the scene can correspond to the field of view of the thermal camera, or the first part of the scene can correspond to a portion of the field of view. The first part of the scene can be the background part of the scene, and the first part of the scene can be selected to have one or more background areas having a common temperature, for example, a common temperature, such that the ambient temperature represents this temperature. For example, it should be understood that it is important to select the first part of the scene so that the temperature of the first part of the scene can be represented by the background areas such that we can say about the ambient temperature, for example, that the ambient temperature and the common temperature are the same or approximately the same. One example is when a first part of the scene is selected such that it is known or assumed to have a temperature that matches and fluctuates with the measured air temperature within the scene. Ambient temperature is the temperature of the air or other medium and surrounding objects within the geographical location of the scene, measured by a thermometer or other temperature indicating device, or received from a weather service. One or more background areas of the first part of the scene may be areas comprising shrubs, trees, fences, facades, or a combination thereof, to name a few examples.

[0019] In this disclosure, the collected ambient temperature and collected thermal image sensor signal values ​​are sometimes collectively referred to as collected calibration data.

[0020] The first period can be a long period, meaning a period of one or more days, one or more months, or even one or more years. Therefore, by collecting calibration data at multiple points in time within the first period, the calibration data can be collected over one or more days, one or more months, or even one or more years. Typically, since the thermal camera is located outdoors and the calibration data is collected during the first period, the collected calibration data can cover a range of ambient temperatures, including daytime and nighttime temperatures as well as seasonally dependent temperatures, and can also cover a range of sensor signal values. It should be understood that the accuracy of the determined calibration function will improve with increasing the range of ambient temperatures and sensor signal values ​​collected, as will the collected calibration data. However, even if the thermal camera is located indoors and therefore not exposed to the same temperature fluctuations, it should be understood that collecting calibration data over a longer period will increase the accuracy of the determined calibration function, as the number of collected calibration data points will increase.

[0021] The calibration function used to determine the temperature of the second part of the scene within the second period can be the most recent calibration function determined. However, it should be understood that the collection of calibration data can continue after the temperature determination, thereby allowing a new, recent calibration function to be determined based on the calibration data collected before and after the most recent temperature determination. This new, recently determined calibration function can then be used for temperature determination at a new point in time within the second period.

[0022] On-the-fly calibration of a thermal camera becomes possible by collecting calibration data from the first part of a scene over a long period of time, while providing a temperature determination within the second part of the scene. Thus, the thermal camera can be calibrated during its normal operation. Updating the calibration function even during normal operation offers the benefit of increasing the number of time points during the first period, thereby increasing the accuracy of the calibration and also taking into account changes within the thermal image sensor over time.

[0023] In another embodiment, the objective is achieved by a thermal camera system for temperature calibration and determination of the temperature within a scene.

[0024] The collection unit is configured to collect ambient temperatures representing the temperature of a first part of the scene at each of several points in time within a first period, in order to obtain collected ambient temperatures over a certain range of ambient temperatures.

[0025] The thermal camera is configured to be positioned in the scene. Furthermore, the thermal camera is configured to collect one or more thermal image sensor signal values ​​at each of several points in time within a first period, corresponding to the collected ambient temperature and related to the first portion of the scene.

[0026] The calibration function determination unit is configured to determine a calibration function based on the collected ambient temperature and one or more thermal image sensor signal values ​​corresponding to each of the collected ambient temperatures. The calibration function provides temperature according to the thermal image sensor values.

[0027] The thermal camera is configured to capture a thermal image of a scene within a second period, which includes thermal image sensor signal values ​​related to the second portion of the scene.

[0028] Furthermore, during the second period, the temperature determination unit is configured to determine the temperature of the second part of the scene based on a calibration function and based on one or more thermal image sensor signal values included in the thermal image captured of the scene and related to the second part of the scene.

[0029] According to another aspect, the object is achieved by a computer program product comprising a computer-readable storage medium having instructions which, when executed by a processor, are adapted to carry out the operations of the method described herein.

[0030] Embodiments will now be described in more detail, by way of example and with reference to the accompanying schematic drawings, in which the same reference signs will be used for like elements.

Brief Description of the Drawings

[0031] [Figure 1A] FIG. schematically shows a calibration function for a fully calibrated thermal camera according to the prior art. [Figure 1B] FIG. schematically shows a calibration function for a standard calibrated thermal camera according to the prior art. [Figure 2] FIG. schematically shows a thermal camera system according to an embodiment. [Figure 3] FIG. is a flowchart of a method for calibration and temperature determination according to an embodiment. [Figure 4] FIG. schematically shows a calibration function for a thermal camera determined according to an embodiment. [Figure 5] FIG. schematically shows a thermal camera system according to an embodiment.

Modes for Carrying Out the Invention

[0032] Embodiments are described more fully hereafter with reference to the accompanying drawings. However, the present invention can be embodied in many different forms and should not be construed as being limited to the embodiments described herein. The systems and devices disclosed herein are described in operation.

[0033] Figure 2 schematically shows a thermal camera system 200, which includes a thermal camera 210 positioned in a scene, for example, a scene of interest for thermal monitoring. The one-dimensional field of view (FOV) of the thermal camera 210 is schematically shown between the two dashed lines. However, it should be understood that the field of view of the thermal camera 210 is two-dimensional.

[0034] The thermal camera 210 can generally be any type of digital thermal image sensor that includes an infrared radiation detector in the form of a thermal image sensor and is capable of capturing a thermal image of a scene based on the infrared radiation emitted from the scene. For example, the thermal camera 210 may be or may be an uncooled thermal camera that includes an internal thermometer. However, the thermal camera 210 may be or may be a cooled thermal camera, such as a thermoelectric cooled thermal camera.

[0035] The thermal camera 210 can be operably connected to the processing device 220 by wire or wirelessly. The processing device 220 can be physically separate from the thermal camera 210, as shown in Figure 2, or the processing device 220 can be integrated into the thermal camera 210. In embodiments where the processing device 220 is physically separated from the thermal camera 210, the processing device 220 is referred to as an external processing device. The thermal camera 210 and the processing device 220 can each be connected to the network 230.

[0036] The processing device 220 and its components can be implemented in software, hardware, or a combination thereof. In particular, the processing device 220 may comprise a processor 222 and memory 224. The memory can function as a (non-temporary) computer-readable storage medium for storing computer code instructions, which, when executed by the processor, are adapted to carry out any of the methods disclosed herein.

[0037] Furthermore, the processing device 220 can be implemented on a computing platform, such as a personal computer, a custom embedded system, a mobile device, or by one or more cameras in a multi-camera system. Some or all of the functions of the processing device 220 in the camera system 200 can be incorporated into software applications such as a video management system (VMS), monitoring tools, or separate temperature calibration and determination applications.

[0038] Network 230 can be any suitable network, such as a wired network, a wireless network, or a combination thereof. The communication network can be a computer network, a telecommunications network, or a combination thereof. For example, Network 230 can be a local area network (LAN), a wide area network (WAN), the Internet, a cellular network, a Wi-Fi network, a cable-based network, an Ethernet-based network, or a combination thereof.

[0039] Figure 3 schematically illustrates an embodiment of a method for temperature calibration and determining the temperature within a scene. A thermal camera 210 is positioned in the scene. The thermal camera 210 operates within a thermal camera system 200 and captures thermal images of the scene. It should be understood that one or more of the operations described below may be optional, and that the operations may be performed in combination or in another appropriate order. operation 301

[0040] At each of several time points within the first period Δt1, the ambient temperature representing the temperature of the first part of the scene is collected.

[0041] Furthermore, at each of several time points within the first period Δt1, the thermal camera 210 collects one or more thermal image sensor signal values ​​that correspond to the collected ambient temperature and are related to the first part of the scene.

[0042] As mentioned earlier, a thermal image sensor can collect thermal images of a scene covered by the field of view of a thermal camera, and the thermal image contains thermal image sensor values ​​from the entire field of view of the thermal camera. Thermal image sensor values ​​are registered by image sensor elements, which are also commonly called pixels of the thermal sensor image.

[0043] As mentioned earlier, the scene can be a scene in which a thermal camera is positioned to monitor it while it is operating, and the first part of the scene can correspond to the field of view of the thermal camera, or the first part of the scene can correspond to a portion of the field of view. Thus, the first part of the scene can correspond to a portion of the field of view of the thermal camera 210, or to the entire field of view of the thermal camera 210. Therefore, the first part of the scene can correspond to a portion of the captured thermal image, or to the entire captured thermal image. As mentioned earlier, the first part of the scene can be the background part of the scene, and the first part of the scene can be selected to have one or more background areas having a certain temperature, for example, a normal temperature such that the ambient temperature indicates this temperature. For example, it should be understood that it is important to select the first part of the scene to have background areas such that the ambient temperature and the normal temperature can be the same or approximately the same temperature. One example is when a first portion of a scene is selected such that it is known or assumed to have a temperature that matches and fluctuates with the measured air temperature within the scene. Ambient temperature is the temperature of the air or other medium and surrounding objects within the geographic location of the scene, measured by a thermometer or other temperature indicating device, or received from a weather service. One or more background areas of the first portion of the scene may be areas comprising, to give some examples, shrubs, trees, fences, facades, or a combination thereof. Regardless of the prior art described above, the idea herein does not use specific objects with known temperatures for calibration. Instead, one or more portions of the image are assumed to have the same temperature as the ambient temperature, which is the temperature measured within the scene, for example, by a thermometer located in or near a thermal imaging sensor, or by a nearby weather station.

[0044] Here are some examples of how to select the first part of a scene.

[0045] In the first example, the first part of the scene is selected, for example, manually, based on one or more image sensor elements that record infrared radiation from one or more suitable scene areas, such as plants, indirectly sunlit areas, and shaded areas, while avoiding surfaces with a glossy finish and surfaces that reflect the sky or sun. These scene areas are considered suitable because their temperatures will be the same as or approximately the same as the ambient temperature of the scene. Identifying these suitable scene areas can be done using image analysis tools such as material classification within the scene. Thus, in an outdoor environment with cloudy weather, most materials within the scene tend to have similar temperatures and will therefore reflect the collected ambient temperature fairly well. Therefore, the collection of calibration data can be concentrated during periods with cloudy weather, and the information can be obtained from real-time weather services.

[0046] In the second example, the first part of the scene is selected by the processor 222 of the thermal camera 210, for example, automatically, by first calculating the average of thermal image sensor signal values ​​from all or some of the image sensor elements that record thermal images, second comparing one or more thermal image sensor signal values ​​to the average, and third determining the first part of the scene to correspond to one or more image sensor elements having thermal image sensor signal values ​​within a certain interval, including the average. This procedure can be repeated by calculating a new average of thermal image sensor signal values ​​based on thermal image sensor signal values ​​within a previous interval, and determining the first part of the scene to correspond to one or more image sensor elements having thermal image sensor signal values ​​within a certain interval, for example, a new interval, including the new average.

[0047] The size of the interval containing the calculated mean can be determined based on the standard deviation of the thermal image sensor signal values ​​used to calculate the mean.

[0048] When calculating the average thermal image sensor signal value, outliers can be excluded. Similarly, in this second example, weather information indicating sunny or cloudy weather can be considered, because typically, signals that deviate from the average in sunny weather are unlikely to correspond to ambient temperature and can be ignored.

[0049] The thermal camera 210, which captures thermal images, has a thermal image sensor 212 comprising multiple image sensor elements. Infrared radiation emitted from a first part of the scene is recorded by the group of image sensor elements. Therefore, the thermal image sensor signal values ​​from this group of thermal sensor elements are associated with the first part of the scene. For each of several time points within a first period Δt1, the thermal camera 210 can collect thermal image sensor signal values ​​associated with the first part of the scene from the thermal image captured at each respective time point.

[0050] In some embodiments, the first period is a long period, such as 24 hours, several days, several weeks, several months, and several years. Thus, calibration data is collected both overnight and during the day over 24 hours, several days, several weeks, several months, or several years. Furthermore, calibration data can be collected over different seasons, for example, spring, summer, autumn, and / or winter. Depending on the length of the first period, the range of ambient temperature collected may vary. In the case of a camera 210 placed in an outdoor scene and where ambient temperature can be collected for a full 24 hours, the collected calibration data may show ambient temperature between the warmest hours of the day and the coldest hours of the night, as well as between several data points in between. In another example, the collected ambient temperature can be collected over an entire year, including the hottest summer day and the coldest winter day. Similarly, in the case of a thermal camera 210 placed in an indoor scene, the first period can be selected so that the collected ambient temperature varies. The length of the first period can be based on a desired range of the collected calibration data. For example, if the difference between the lowest and highest collected ambient temperatures is small, the length of the first period can be increased until the difference between the lowest and highest collected ambient temperatures becomes larger, for example, to give a few examples, it can exceed a threshold such as 5, 10, 20, 30, or 40°C.

[0051] Depending on the application, different temperature ranges of collected ambient temperatures may be required to obtain an acceptable accuracy for the calibration function. For example, if a person is monitored by the thermal camera 210, the ambient temperature range used to determine the calibration function may be within the range of 25 to 40°C. As another example, if the thermal camera 210 is calibrated for a hot machine, a larger, i.e., different interval of ambient temperature is required, or a greater uncertainty in the calibration function must be acceptable. Therefore, the first period should be selected to be long enough to incorporate the desired temperature range.

[0052] In some embodiments, the first period is as long as the lifespan of the thermal camera 210. Therefore, as long as the thermal camera 210 is operating in the operating location, calibration data can be collected, and the calibration function can be updated and made more accurate, or a new calibration function can be determined. However, it should be understood that a new first period can be started at any point during the operation of the thermal camera 210, and the calibration data collected during this new first period can be used to determine a new calibration function. Furthermore, a new first period can be started after a standby or switch-off period, during which the thermal camera 210 may have been repositioned. The advantage of using the most recently collected calibration data to determine the calibration function is that the calibration can reflect the latest operating state of the thermal camera.

[0053] In some embodiments, one or more of the collected ambient temperatures are measured by a thermometer 214, as schematically shown in Figure 2. The thermometer 214 may be an internal thermometer, for example, a printed circuit board (PCB) thermometer included in the thermal camera 210, or the thermometer 214 may be an external thermometer located in or outside the scene outside the thermal camera 210. The thermometer 214 may also be a remote sensing thermometer, i.e., a thermometer located at a distance from the scene and in wired or wireless communication with the thermal camera system 200, for example, via a network 230.

[0054] Alternatively or additionally, one or more of the collected ambient temperatures are temperatures collected from a real-time weather service. Therefore, in some embodiments, the thermal camera system 200 can receive or retrieve ambient temperatures from a real-time weather service via the network 230.

[0055] For example, the collected ambient temperature represents an ambient temperature within the range of approximately -40°C to +50°C. Therefore, the collected ambient temperature represents the ambient temperature in the normal operating environment for the thermal camera 210. operation 302

[0056] The calibration function is determined based on the collected ambient temperature and one or more thermal image sensor signal values ​​corresponding to each of the collected ambient temperatures. As previously mentioned, the collected ambient temperature represents the temperature of a first part of the scene, and the thermal image sensor values ​​collected during a first period are related to the first part of the scene. The calibration function gives the temperature according to the thermal image sensor values. Figure 4 shows an example of a calibration function. The example calibration function is determined based on collected ambient temperatures in the range of 10 to 40°C and on a number of collected sensor signal values ​​in the figure, displayed digital signals. In Figure 4, the y-axis represents temperature in °C, and the x-axis represents image sensor signal values ​​as integers. The calibration function for the thermal camera 210 can be determined in real time after the thermal camera is manufactured. Preferably, the calibration function is determined in situ, i.e., at the installation site for the thermal camera 210 and during the operation of the thermal camera 210. Therefore, calibration does not need to be performed at the manufacturing site. However, it should be understood that the calibration function can be determined at a first location, i.e., the calibration site, and then the determined calibration can be used by a thermal camera 210 located at a second location, for example, the operating site, and may similarly be further improved.

[0057] The calibration function can be determined by the thermal camera 210, for example, by the processing device 220 when it is included in the thermal camera 210. Alternatively or additionally, the calibration function can be determined by an external processing device, for example, a second instance of the processing device 220, which is located outside and in communication with the thermal camera 210. The thermal camera 210 can be operated by wired or wireless connection to the external processing device.

[0058] In some embodiments, the calibration function is determined as a function fit between the collected ambient temperature and the corresponding collected thermal image sensor signal value. Therefore, the calibration function can be a function that best fits all collected ambient temperatures and all corresponding collected thermal image sensor signal values. The calibration function can be expressed, for example, as a mathematical formula or a lookup table. The determination of the calibration function can incorporate one or more temperature thresholds. In this scenario, if the thermal image sensor signal value measured during a second period exceeds a certain value, this indicates that the determined temperature exceeds a predetermined temperature.

[0059] Therefore, the calibration function can be determined as a formula, as a lookup table, or as one or more thresholds.

[0060] For at least one of the collected ambient temperatures, the average of one or more thermal image sensor signal values ​​corresponding to the collected ambient temperature can be used when determining the calibration function. For example, the average of a number of sensor signal values, e.g., 25, corresponding to the collected ambient temperature at the same point in time within a first period can be used when determining the calibration function. The 25 sensor signal values ​​can be obtained from 25 thermal image sensor elements arranged in a 5x5 matrix. The reasons for using the average of sensor signal values ​​instead of all individual sensor signal values ​​include, to name a few, reducing the number of sensor signal values ​​that need to be stored, reducing the possible errors in individual sensor signal values, or reducing the possible noise in individual sensor signal values. For example, by using the average of 25 sensor signal values, only the averaged sensor signal value needs to be stored and used when determining the calibration function, thereby reducing the amount of storage and processing resources required.

[0061] Alternatively or additionally, one or more of the collected thermal image sensor signal values ​​used in determining the calibration function may be at least one of the collected thermal image sensor signal values ​​collected at the same time point in a first period.

[0062] Determining the calibration function may further involve extrapolating the calibration function to thermal image sensor signal values ​​that give temperatures outside the range of the collected ambient temperature. The extrapolation may be a linear extrapolation of the collected calibration data. By extrapolating the calibration function, it can be used to determine temperatures in a scene that are outside the temperature range of the collected calibration data. For example, extrapolation of the calibration function is necessary when the thermal camera 210 should be able to indicate or trigger a fire alarm when an object or part of a scene has a temperature above 250°C, because it would be impossible to collect calibration data containing such high temperatures.

[0063] As previously mentioned, calibration data is collected during the first period. Furthermore, as previously mentioned, one or more new first periods can be started, and new calibration data can be collected. For each first period, for each new first period, or for a part thereof, a calibration function can be determined. It should be understood that one or more of the determined calibration functions can be stored along with their respective timestamps. The timestamp can indicate one or more points in time within a period, such as the start, middle, or end time, during which the calibration data used in determining the calibration function was collected. The stored calibration function associated with the timestamp can be used at a later time to determine the temperature of a thermal image captured at a time corresponding to or close to the time indicated by that timestamp. Therefore, the stored timestamp can be used when determining which of the multiple stored calibration functions to use in determining the temperature of a thermal image captured at a certain time. The method for determining the temperature of the captured thermal image is described in more detail in operation 304 below.

[0064] It should be understood that the determined calibration function can be used by one or more additional thermal cameras of the same type as thermal camera 210. Therefore, even if not shown in the figures, the thermal camera system 200 may comprise multiple thermal cameras 210 of the same type. However, one or more thermal cameras of the same type as thermal camera 210 included in the thermal camera system 200 may also be thermal cameras included in different camera systems. As used in this disclosure, the expression “thermal cameras of the same type” means that the thermal cameras comprise one or more image sensors of the same type. operation 303

[0065] The thermal camera 210 captures a thermal image of the scene, including thermal image sensor signal values ​​related to a second portion of the scene, within a second period Δt2.

[0066] In some embodiments, the thermal camera 210 captures a thermal image of the scene at a first time point within a second period Δt2.

[0067] The second period may not overlap with the first period. For example, this may be the case when the first period, during which calibration data, such as ambient temperature indicating the temperature of a first part of the scene and thermal image sensor signal values ​​associated with the first part of the scene, is collected, precedes the second period during which the thermal image of the scene is captured. In such a scenario, the calibration data is collected and the calibration function is determined before the thermal image of the scene is captured.

[0068] However, it should be understood that the second period may at least partially overlap with the first period. This is true when calibration data collection takes place over a long period, for example, one or more days, one or more months, or even one or more years, and when the acquisition of thermal images of the scene takes place at a first point in time within the second period Δt2, which is also included in the first period Δt1. Calibration data collection can continue after the acquisition of thermal images, and a new or updated calibration function can be determined based on all the calibration data collected within the first period Δt1. It should be understood that the sensor signal values ​​of the images acquired at a first point in time within the second period Δt2 can be used in determining the calibration function before determining the temperature of the scene.

[0069] The first and second parts of the scene can correspond to at least the first and second parts of the field of view of the thermal camera 210, respectively. However, in the case of different zoom settings of the thermal camera 210, the first and second parts of the scene can correspond to the first part of the first field of view and the second part of the second field of view of the thermal camera 210, respectively. This can be seen, for example, when calibration data is collected using the first field of view of the thermal camera 210, and the thermal image used to determine the temperature is captured using a different second field of view of the thermal camera. As one example, the first part of the scene from which the calibration data is collected may be a field of view with a wide-angle zoom setting, and the second part of the scene from which the temperature determination is performed may be a field of view with a telephoto zoom setting, or the order may be reversed, with the zoom set to telephoto for the first part of the scene and wide-angle for the second part.

[0070] In some embodiments, the first and second parts of a scene are non-overlapping parts of the scene. This may be the case when the first part of the scene used for acquiring calibration data does not overlap with the second part of the scene in which the temperature determination is performed. Some examples of when it is advantageous to use non-overlapping parts of a scene are when the second part of the scene contains noisy objects, such as moving objects or objects that provide unstable image sensor signals. These noisy objects would obscure the calibration data acquired within the first part of the scene if the first part of the scene overlapped with the second part of the scene. In such scenarios, more accurate and stable calibration data would be acquired when the first and second parts of the scene do not overlap.

[0071] Alternatively, the first and second parts of a scene are at least partially overlapping parts of the scene. This can be said to be true when the first part of the scene used for collecting calibration data at least partially overlaps with the second part of the scene in which the temperature determination is performed. One example of when it may be advantageous to use at least partially overlapping parts of a scene is when the first part of the scene, which includes trees, is used to collect calibration data and determine a calibration function, and the second part of the scene, which at least partially overlaps, is used to determine the fire of one of the trees. operation 304

[0072] During the second period, the temperature of the second portion of the scene is determined based on a calibration function and on one or more thermal image sensor signal values ​​included in the thermal image of the scene and related to the second portion of the scene.

[0073] In some embodiments, the temperature of a second portion of the scene is determined at a second time point within a second period. The second time point may be different from and follow a first time point. As described above, a thermal image can be captured by the thermal camera 210 at a first time point within the second period.

[0074] The temperature can be determined by the thermal camera 210, for example, by the processing device 220 when included in the thermal camera 210. The temperature can be determined based on a calibration function and the average of the thermal image sensor signal values ​​included in the captured image and related to a second part of the scene.

[0075] Alternatively or additionally, the temperature can be determined by an external processing device, for example, a processing device 220, for example, a second instance of processing device 220, which is located outside and in communication with the thermal camera 210. The temperature can be determined based on a calibration function and the received average of thermal image sensor signal values ​​related to the second part of the scene.

[0076] As mentioned above, the second period may not overlap with the first period. For example, this may be the case when the first period, during which calibration data, such as ambient temperature representing the ambient temperature of a first part of the scene and thermal image sensor signal values, is collected, precedes the second period during which the temperature determination of the scene is made. In such a scenario, the calibration function is determined before the temperature determination of the scene.

[0077] However, as mentioned above, it should be understood that the second period may at least partially overlap with the first period. This is true when calibration data collection takes place over a long period, for example, one or more days, one or more months, or even one or more years, and when the scene temperature is determined at a point in time, a second point in the second period, which is also included in the first period, using the latest version of the calibration function at that second point in time. Calibration data collection can continue after the temperature determination, and a new, updated calibration function can be determined based on all the calibration data collected within the first period, i.e., calibration data collected both before and after the temperature determination. It should be understood that sensor signal values ​​of images captured at a point in time, for example, a first point in the second period, can be used in determining the calibration function before the scene temperature is determined.

[0078] The calibration function can be determined, for example, based on selected calibration data, such as data selected primarily or solely on later points in time within a first period.

[0079] The determination of the temperature of the second part of the scene at the second time point within the second period can be carried out in connection with the acquisition of image data at the first time point within the second period.

[0080] In another example, the acquisition of image data at a first point in time within a second period may involve storing the acquired image data in appropriate image data storage, for example, in memory 224. The following step of determining the temperature of a second part of a scene at a second point in time within a second period can be performed once when information regarding the temperature of the second part of the scene in the acquired image is actually needed. At this time, a calibration function determined using any of the methods described above is used. Thus, the temperature determination of the second part of the scene can be performed in a previously acquired image. As described above, one or more of the determined calibration functions can be stored along with their respective timestamps. The timestamps can indicate one or more points in time during which the calibration data used in determining the calibration function was collected. Therefore, a stored calibration function associated with a timestamp can be used at a later point in time to determine the temperature of a thermal image acquired at a point in time corresponding to or close to the point indicated by that timestamp. Alternatively, a calibration function created using calibration data collected over a longer period, including both points in time before and after the first and second points in the second period, can be used. This is because it may provide a more accurate calibration function. operation 305

[0081] In some embodiments, an alarm is triggered when the thermal image sensor signal value in the captured thermal image indicates a temperature exceeding a temperature threshold. The temperature threshold can be set based on a calibration function. For example, the temperature threshold can be set to indicate an increased temperature, e.g., an excessively high temperature, within an object included in the captured image. For example, the temperature threshold can be set to indicate a fire in the captured image. In such cases, the temperature threshold can be set to, for example, 70°C. However, the temperature threshold can also be set to -40°C to indicate that a chilled item has exceeded its maximum desired temperature, or to +40°C for electronic devices such as computer servers to indicate that an electronic device has exceeded its maximum desired temperature.

[0082] An alarm can be an audible alarm, a visual alarm, another form of alarm signal, or a combination thereof.

[0083] Furthermore, an alarm can be indicated by the thermal camera 210, and / or by the external processing device 220.

[0084] For example, an alarm can be triggered when the thermal image sensor signal value in the captured thermal image indicates a fire in a second part of the scene.

[0085] Embodiments of the thermal camera system 200 for calibration and temperature determination are described here with reference to Figure 5. As previously mentioned, the thermal camera 210 and processing device 220 are configured to operate within the system 200. Furthermore, the thermal camera 210 is configured to capture a thermal image of the scene. As previously mentioned, the thermal camera system 200 for temperature calibration and temperature determination in a scene comprises the thermal camera 210.

[0086] The thermal camera system 200 includes a collection unit 216 configured to collect ambient temperature data indicating the temperature of a first portion of a scene at each of several points in time within a first period. In Figure 5, the collection unit 216 is shown as part of the thermal camera 210. However, it should be understood that the collection unit 216 can be located outside the thermal camera 210. For example, the collection unit 216 can be included in a processing device 220, and the processing device 220 can be included in the thermal camera 210 or located in communication with the thermal camera 210.

[0087] In some embodiments, the collection unit 216 is configured to receive ambient temperatures collected from a thermometer 214 configured to measure one or more of the collected ambient temperatures. Alternatively or additionally, the collection unit 216 may be configured to collect one or more of the collected ambient temperatures from a real-time weather service.

[0088] The thermal camera 210 is configured to be positioned in the scene and to collect one or more thermal image sensor signal values ​​corresponding to the collected ambient temperature and related to the first part of the scene at each of a plurality of points in time within a first period.

[0089] The thermal camera system 200 includes a calibration determination unit 226-1 configured to determine a calibration function based on the collected ambient temperature and one or more collected thermal image sensor signal values ​​corresponding to the collected ambient temperature and related to a first portion of the scene. As previously mentioned, the calibration function provides temperature in accordance with the thermal image sensor signal values.

[0090] The calibration determination unit 226-1 can be configured in communication with the acquisition unit 216 to obtain, for example, receive or retrieve the collected ambient temperature used in determining the calibration function.

[0091] The calibration function determination unit 226-1 is included in the processing device 220. As previously mentioned, the processing device 220 can be included in the thermal camera 210. Alternatively or additionally, the processing device 220 or a second instance of the processing device 220 may be an external processing device configured to be located outside the thermal camera 210 and in communication with the thermal camera 210.

[0092] In some embodiments, when a processing device 220 comprising an acquisition unit 216 and a calibration function determination unit 226-1 is located outside the thermal camera 210, the acquisition of ambient temperature and determination of the calibration function are performed outside the thermal camera 210. In such embodiments, the thermal camera 210 obtains, for example, receives or retrieves the calibration function from the processing device 220. The calibration function can be associated with a time point in time or a period, for example, a timestamp indicating a first period, when the calibration data was acquired.

[0093] The calibration function determination unit 226-1 can be configured to determine the calibration function as a function fit between the collected temperature and the corresponding collected thermal image sensor signal value.

[0094] One or more of the corresponding collected thermal image sensor signal values ​​used in determining the calibration function may be the average of thermal image sensor signal values ​​collected at the same point in time within a first period. This means that for at least one of the collected ambient temperatures, the average of one or more thermal image sensor signal values ​​corresponding to the collected ambient temperature is used in determining the calibration function.

[0095] Alternatively or additionally, one or more of the corresponding collected thermal image sensor signal values ​​used in determining the calibration function may be at least one of the collected thermal image sensor signal values ​​collected at the same time point in a first period.

[0096] In some embodiments, the calibration function determination unit 226-1 is configured to extrapolate the calibration function to thermal image sensor signal values ​​that give temperatures outside the range of collected ambient temperatures.

[0097] Furthermore, the thermal camera 210 is configured to capture a thermal image of the scene, including thermal image sensor signal values ​​related to a second portion of the scene, within a second period. In some embodiments, the thermal camera 210 is configured to capture a thermal image at a first point in time within the second period.

[0098] The thermal camera system 200 includes a temperature determination unit 226-2 configured to determine the temperature of a second portion of a scene within a second period. In some embodiments, the temperature determination unit 226-2 is configured to determine the temperature at a second point in time within the second period.

[0099] Furthermore, the temperature determination unit 226-2 is configured to determine the temperature based on a calibration function and on one or more thermal image sensor signal values ​​included in the thermal image of the scene and related to the second part of the scene. As described above, the thermal image may be captured by the thermal camera 210 at a first time point in the second period.

[0100] The first and second parts of the scene can correspond to at least the respective first and second parts of the field of view of the thermal camera 210.

[0101] The temperature determination unit 226-2 can be configured to determine the temperature of the second part of the scene based on a calibration function and based on the average of the thermal image sensor signal values ​​related to the second part of the scene.

[0102] In some embodiments, the temperature determination unit 226-2 is configured to trigger an alarm when the thermal image sensor signal value in the acquired thermal image indicates a temperature exceeding a temperature threshold, which is set based on a calibration function.

[0103] It should be understood that the calibration function determination unit 226-1 and temperature determination unit 226-2 described above may be two separate units included in the processing device 220, or they may be a single determination unit 226 included in the processing device 220.

[0104] The thermal camera system 200 includes a thermometer 214 configured to measure one or more of the temperatures to be collected. As previously mentioned, the thermometer 214 may be included in the thermal camera 210, or the thermometer 214 may be a thermometer located outside the thermal camera 210.

[0105] In some embodiments, the thermal camera system 200 is configured to collect one or more of the collected ambient temperatures from a real-time weather service, for example, by a collection unit 216. This can be done, for example, by communicating with the real-time weather service via a network 230, thereby allowing the ambient temperatures to be received or retrieved from the real-time weather service via the network 230.

[0106] Embodiments of this specification also relate to computer program products comprising a computer-readable storage medium having instructions, wherein, when executed by a processor, the instructions are adapted to perform any of the operations described herein.

[0107] Those skilled in the art will recognize that the embodiments described above can be modified in many ways and the advantages of the present invention shown in the embodiments can still be used. Therefore, the present invention should not be limited to the embodiments shown, but rather defined only by the appended claims. Furthermore, the embodiments shown can be combined, as those skilled in the art will understand.

Claims

1. 1. A method for temperature calibration of a thermal camera configured to be placed in a scene and for determining a temperature within said scene, comprising: collecting ambient temperatures indicative of a temperature of a first portion of the scene at each of a plurality of time points within a first time period to obtain collected ambient temperatures spanning a range of ambient temperatures, and collecting, by a thermal camera, one or more thermal image sensor signal values ​​corresponding to each of the collected ambient temperatures and associated with the first portion of the scene to generate a plurality of thermal image sensor signal values, the first portion of the scene including one or more background areas from which the one or more thermal image sensor signal values ​​are collected; determining a calibration function as a function applied to a plurality of the collected ambient temperatures and the plurality of thermal image sensor signal values, the calibration function providing a temperature as a function of the thermal image sensor values; and capturing, within a second time period, by the thermal camera, a thermal image of the scene including thermal image sensor signal values ​​associated with a second portion of the scene; and determining a temperature of the second portion of the scene based on the calibration function and based on one or more of the thermal image sensor signal values ​​included in the captured thermal image of the scene and associated with the second portion of the scene. A method comprising:

2. The first period and the second period are - non-overlapping periods, and - At least partially overlapping periods The method of claim 1 , wherein the first and second electrodes are one of:

3. The method of claim 1 , wherein one or more of the collected ambient temperatures are measured by a thermometer or collected from a real-time weather service.

4. The method of claim 1 , wherein the collected ambient temperature indicates an ambient temperature within a range of approximately −40° C. to +50° C.

5. The method of claim 1 , wherein for at least one of the collected ambient temperatures, an average of the one or more thermal image sensor signal values ​​corresponding to the collected ambient temperature is used in determining the calibration function.

6. Determining the calibration function comprises: - extrapolating said calibration function for thermal image sensor signal values ​​that give temperatures outside said range of collected ambient temperatures. The method of claim 1 further comprising:

7. Determining the temperature of the second portion of the scene includes: determining the temperature based on the calibration function and an average of the thermal image sensor signal values ​​associated with the second portion of the scene; The method of claim 1 further comprising:

8. The first and second portions of the scene are the non-overlapping parts of said scenes, and at least partially overlapping portions of said scenes; The method of claim 1 , wherein the first and second electrodes are one of:

9. - indicating an alarm when a thermal image sensor signal value in a captured thermal image indicates a temperature that exceeds a temperature threshold. The method of claim 1 further comprising:

10. A thermal camera system for temperature calibration of a thermal camera arranged to be placed in a scene and for determining a temperature within said scene, the thermal camera system comprising: said thermal camera; a collection processor configured to collect ambient temperatures indicative of a temperature of a first portion of the scene to obtain collected ambient temperatures spanning a range of ambient temperatures at each of a plurality of time points within a first time period; a calibration function determination processor; - Temperature determination processor; Equipped with the thermal camera is configured to collect one or more thermal image sensor signal values ​​corresponding to the collected ambient temperatures and associated with the first portion of the scene to generate a plurality of thermal image sensor signal values ​​at each of a plurality of time points within the first time period; the first portion of the scene includes one or more background areas from which the one or more thermal image sensor signal values ​​are collected; The calibration function determination processor is configured to determine a calibration function as a function applied to a plurality of the collected ambient temperatures and the plurality of thermal image sensor signal values, the calibration function providing a temperature as a function of the thermal image sensor values; the thermal camera is configured to capture a thermal image of the scene during a second time period, the thermal image including thermal image sensor signal values ​​associated with a second portion of the scene; the temperature determination processor is configured to determine a temperature of the second portion of the scene within the second time period based on the calibration function and based on one or more thermal image sensor signal values ​​included in the captured thermal image of the scene and associated with the second portion of the scene.

11. 11. The thermal camera system of claim 10, wherein the collection processor is configured to receive the collected ambient temperatures from a thermometer configured to measure one or more of the collected ambient temperatures, and / or the collection processor is configured to collect one or more of the collected ambient temperatures from a real-time weather service.

12. The calibration function determination processor and the temperature determination processor: a processing device included in the thermal camera; and an external processing device configured to be disposed external to and in communication with the thermal camera; The thermal camera system of claim 11 , wherein the thermal camera system is included in at least one of the following:

13. The calibration function determination processor, - extrapolating said calibration function to thermal image sensor signal values ​​that give temperatures outside said range of collected temperatures. The thermal camera system of claim 11 configured as follows:

14. The temperature determination processor includes: determining the temperature of the second portion of the scene based on the calibration function and an average of the thermal image sensor signal values ​​associated with the second portion of the scene; and / or The temperature determination processor includes: - indicating an alarm when the thermal image sensor signal value in the captured thermal image indicates a temperature that exceeds a temperature threshold; The thermal camera system of claim 11 configured as follows:

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