Calibration system, calibration method, and calibration program

Abstract

In this calibration system for an infrared camera mounted on a vehicle, a processor is configured to execute: acquiring a target image (Iit) by capturing, from the infrared camera, a target unit in which at least one of high emissivity areas and low emissivity areas, which are adjacent, are two-dimensionally arrayed as a target area; and extracting respective feature point coordinates (Cp) of a plurality of target areas captured in the target image (Iit) to calibrate a characteristic parameter (Pc) in accordance with a relative positional relationship between the feature point coordinates (Cp) for each target area. In particular, the acquisition of the target image includes capturing from the infrared camera the target unit in which a temperature difference (∆T) between the high emissivity areas and the low emissivity areas is controlled such that the high emissivity areas have a higher temperature than the low emissivity areas, to acquire the target image.

Description

Calibration system, calibration method, and calibration program CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Patent Application No. 2024-109002 filed in Japan on July 5, 2024, and the contents of the original application are incorporated by reference in their entirety.

[0002] The present disclosure relates to a calibration technique for calibrating characteristic parameters of a camera.

[0003] The technology disclosed in Patent Document 1 captures an image of a checkered pattern, in which black and white areas are arranged two-dimensionally in a checkered pattern, using a camera. As a result, the technology disclosed in Patent Document 1 extracts the coordinates of intersections of boundary lines in the checkered pattern captured in the captured image, and calibrates the characteristic parameters of the camera based on the coordinates of these intersections.

[0004] Patent No. 6906177

[0005] When the technology disclosed in Patent Document 1 is applied to an infrared camera mounted on a vehicle, the calibration environment is a relatively large indoor space. In this case, it has been found that in a checkered pattern captured in a captured image, the boundaries between black and white areas become blurred due to the influence of, for example, ambient light in the indoor space. Therefore, there is a concern that the accuracy of extracting intersection coordinates at the boundaries between the areas may deteriorate, which may ultimately deteriorate the accuracy of calibration.

[0006] An object of the present disclosure is to provide a calibration system that improves calibration accuracy. Another object of the present disclosure is to provide a calibration method that improves calibration accuracy. Yet another object of the present disclosure is to provide a calibration program that improves calibration accuracy.

[0007] The technical means of the present disclosure for solving the problems will be described below.

[0008] A first aspect of the present disclosure is a calibration system having a processor for calibrating characteristic parameters of an infrared camera mounted on a vehicle, configured to acquire a target image by photographing, with the infrared camera, a target unit in which at least one of adjacent high emissivity areas and low emissivity areas with a difference in emissivity is arranged two-dimensionally as a target area, and to calibrate the characteristic parameters according to the relative positional relationship between the feature point coordinates for each target area by extracting feature point coordinates of multiple target areas shown in the target image, wherein the acquisition of the target image includes acquiring the target image by photographing, with the infrared camera, a target unit in which the temperature difference between the high emissivity area and the low emissivity area is controlled so that the high emissivity area is hotter than the low emissivity area.

[0009] A second aspect of the present disclosure is a calibration method executed by a processor to calibrate characteristic parameters of an infrared camera mounted on a vehicle, the method comprising: acquiring a target image by photographing, with the infrared camera, a target unit in which at least one of adjacent high emissivity areas and low emissivity areas with a difference in emissivity is arranged two-dimensionally as a target area; and calibrating the characteristic parameters according to the relative positional relationship between the feature point coordinates of each target area by extracting feature point coordinates of multiple target areas shown in the target image, wherein the acquisition of the target image comprises acquiring the target image by photographing, with the infrared camera, a target unit in which the temperature difference between the high emissivity area and the low emissivity area is controlled so that the high emissivity area is hotter than the low emissivity area.

[0010] A third aspect of the present disclosure is a calibration program stored in a storage medium for calibrating characteristic parameters of an infrared camera mounted on a vehicle, the calibration program including instructions for causing a processor to execute the calibration, the program including instructions for executing the following: acquiring a target image by photographing, with the infrared camera, a target unit in which at least one of adjacent high emissivity areas and low emissivity areas with a difference in emissivity is arranged two-dimensionally as a target area; and calibrating the characteristic parameters according to the relative positional relationship between the feature point coordinates for each target area by extracting feature point coordinates of multiple target areas shown in the target image, wherein the acquisition of the target image includes acquiring the target image by photographing, with the infrared camera, a target unit in which the temperature difference between the high emissivity area and the low emissivity area is controlled so that the high emissivity area is hotter than the low emissivity area.

[0011] In the first to third aspects, target units are arranged two-dimensionally, with at least one of high emissivity areas and low emissivity areas adjacent to each other with a difference in emissivity, and the target units are photographed by an infrared camera mounted on a vehicle. Then, by extracting the feature point coordinates of the multiple target areas shown in the target image obtained by photographing, the characteristic parameters are calibrated according to the relative positional relationship between the feature point coordinates of each target area.

[0012] Here, the target units according to the first to third aspects are photographed by an infrared camera and appear in a target image while the temperature difference between the high-emissivity areas is controlled so that the high-emissivity areas are hotter than the low-emissivity areas. This allows for a contrast in infrared brightness at the boundary between the high-emissivity and low-emissivity areas, where a radiation energy difference can be ensured based on the controlled temperature difference. This makes it possible to improve the accuracy of extracting feature point coordinates and, ultimately, the accuracy of calibrating characteristic parameters for each target area whose boundary can be accurately identified as at least one of a high-emissivity area and a low-emissivity area.

[0013] 1 is a block diagram showing the overall configuration of a first embodiment; FIG. 2 is a block diagram showing the configuration of a calibration system according to the first embodiment; FIG. 3 is a front view showing a target unit of the calibration system according to the first embodiment; FIG. 4 is a flowchart showing an external calibration flow according to the first embodiment; FIG. 5 is a top view for explaining the external calibration flow according to the first embodiment; FIG. 6 is a schematic view showing a target image acquired in the external calibration flow according to the first embodiment; FIG. 7 is a schematic view for explaining the internal calibration flow according to the first embodiment; FIG. 8 is a perspective view for explaining the internal calibration flow according to the first embodiment; FIG. 9 is a schematic view showing a target image acquired in the internal calibration flow according to the first embodiment; FIG. 10 is a schematic view for explaining the internal calibration flow according to the first embodiment; FIG. 11 is a block diagram showing the configuration of a calibration system according to a second embodiment; FIG. 12 is a front view showing a target unit of a calibration unit according to a third embodiment; FIG. 13 is a schematic view for explaining the external calibration flow and the internal calibration flow according to the third embodiment; FIG. 14 is a front view showing a target unit of a calibration unit according to a fourth embodiment; FIG. 15 is a schematic view for explaining the external calibration flow and the internal calibration flow according to the fourth embodiment; FIG. 16 is a front view showing a target unit of a calibration unit according to a fifth embodiment; FIG. 17 is a schematic view for explaining the external calibration flow and the internal calibration flow according to the fifth embodiment. FIG. 10 is a front view showing a target unit of a calibration unit according to a modification of the first and third embodiments.

[0014] Hereinafter, multiple embodiments of the present disclosure will be described with reference to the drawings. Note that corresponding components in each embodiment are designated by the same reference numerals, and redundant description may be omitted. Furthermore, when only a portion of the configuration is described in each embodiment, the configuration of another previously described embodiment may be applied to the remaining portions of the configuration. Furthermore, in addition to the combinations of configurations explicitly stated in the description of each embodiment, configurations of multiple embodiments may be partially combined together even if not explicitly stated, provided that there is no particular problem with the combination.

[0015] 1 is constructed to calibrate the characteristic parameter Pc of an infrared camera 3 mounted on a host vehicle 2. The calibration system 1 is therefore installed in a calibration facility, such as a production facility or maintenance facility for the host vehicle 2. Such a host vehicle 2 corresponds to a vehicle that is placed in an interior space 9 of the calibration facility (see FIGS. 5 and 9 described below) and is the subject of calibration, out of multiple vehicles that require calibration of the mounted infrared camera 3.

[0016] As shown in FIG. 2 , the infrared camera 3 to be calibrated by the calibration system 1 includes a memory 30, an image sensor 31, a lens system 32, and an image sensor circuit 33. The image sensor 31 is a semiconductor element, such as a microbolometer, having a plurality of pixels arranged vertically and horizontally. The image sensor 31 captures an infrared light image, pixel by pixel, of a target present within the imaging field of view through the lens system 32, the infrared light image received in the infrared range, particularly in the far-infrared range (e.g., a wavelength range of 7 to 14 μm, etc.) in this embodiment. The image sensor circuit 33 is a semiconductor chip, such as an image processing circuit, that processes the image signal from each pixel of the image sensor 31. The image sensor circuit 33 samples the infrared luminance corresponding to the radiant energy of the infrared light image received within the imaging field of view, pixel by pixel, and converts the infrared luminance into digital data, thereby outputting an infrared image Ii.

[0017] 1, the transmission output of the infrared image Ii from the host vehicle 2 to the calibration system 1 is realized by data transmission via a communication network between the two systems 2 and 1. In addition, an output command Oi from the calibration system 1 to command the host vehicle 2 to output the infrared image Ii is realized by data transmission via the communication network between the two systems 1 and 2.

[0018] The characteristic parameters Pc of the infrared camera 3 include external parameters Pco and internal parameters Pci. The external parameters Pco are defined by matrix parameters for transforming a world coordinate system outside the infrared camera 3 into the camera coordinate system of the infrared camera 3 itself. The internal parameters Pci are defined by matrix parameters for transforming the camera coordinate system of the infrared camera 3 itself into the image coordinate system of the infrared image Ii. From these definitions, the characteristic parameters Pc are given as a camera matrix by the matrix product of the external parameters Pco and the internal parameters Pci according to the following equation 1:

[0019] The calibration system 1 outputs calibration data Dc to provide the host vehicle 2 with calibrated characteristic parameters Pc for the infrared camera 3 mounted on the host vehicle 2. The transmission output of the calibration data Dc from the calibration system 1 to the host vehicle 2 is achieved by data transmission via a communication network between the calibration system 1 and the host vehicle 2. The calibration data Dc provided to the host vehicle 2 is stored in the memory 30 of the infrared camera 3. The characteristic parameters Pc represented by the calibration data Dc stored in the memory 30 are used for photographing from the infrared camera 3.

[0020] The calibration system 1 has a display unit 5, an input unit 6, a target unit 7, and a processing computer 10. The display unit 5 is, for example, a liquid crystal panel or an organic EL panel, etc., that displays data to an operator of the calibration system 1. The input unit 6 is, for example, at least one of a mouse, a trackball, a keyboard, etc., that receives input from the operator of the calibration system 1.

[0021] 1 to 3 has a plurality of high emissivity areas 70 and a plurality of low emissivity areas 71 adjacent to each other with a difference in emissivity. In the first embodiment, both the high emissivity areas 70 and the low emissivity areas 71 are two-dimensionally arranged as rectangular target areas 72 as shown in Fig. 3 in a checkerboard pattern alternating vertically and horizontally (up and down and left and right in the installation state shown in Figs. 5 and 9 described below). Note that the number of vertical and horizontal arrangements shown in Fig. 3 is merely an example, and the number of arrangements may be the same or different for the calibration of the external parameter Pco and the calibration of the internal parameter Pci described below.

[0022] At least the surface of each high-emissivity area 70 (the front surface facing the host vehicle 2 in the installation state shown in FIGS. 5 and 9 ) has an emissivity of, for example, 0.7 or more, preferably 0.8 or more, and more preferably 0.9 or more. Therefore, at least the surface of each high-emissivity area 70 may be made of a material such as black paint, black vinyl resin, black rubber, or black cloth. Meanwhile, at least the surface of each low-emissivity area 71 (the front surface facing the host vehicle 2 in the installation state shown in FIGS. 5 and 9 ) has an emissivity of, for example, 0.3 or less, preferably 0.2 or less, and more preferably 0.1 or less. Therefore, at least the surface of each low-emissivity area 71 may be made of a material such as aluminum, copper, stainless steel, or glass.

[0023] The target unit 7 has a plurality of heating elements 73 and cooling elements 74 shown in FIGS. 1 and 2 . The heating elements 73 are two-dimensionally arranged to correspond one-to-one to the high-emissivity areas 70. Each heating element 73 is formed, for example, by a Peltier element. Each heating element 73 is arranged with its heat-generating surface in contact with the back surface of its corresponding high-emissivity area 70 (the back surface in the installation state shown in FIGS. 5 and 9 ), thereby enabling heating of the corresponding area 70. Meanwhile, each cooling element 74 is two-dimensionally arranged with a one-to-one correspondence to the low-emissivity areas 71. Each cooling element 74 is formed, for example, by a Peltier element. Each cooling element 74 is arranged with its heat-absorbing surface in contact with the back surface of its corresponding low-emissivity area 71 (the back surface in the installation state shown in FIGS. 5 and 9 ), thereby enabling cooling of the corresponding area 71. The heating of the high emissivity area 70 by each heating element 73 and the cooling of the low emissivity area 71 by each cooling element 74 are controlled by the processing computer 10 .

[0024] 1, the dedicated computer constituting the processing computer 10 has at least one memory 11 and one processor 12. The memory 11 is at least one type of non-transitory tangible storage medium, such as a semiconductor memory, a magnetic medium, or an optical medium, that non-temporarily stores computer-readable programs, data, and the like.

[0025] In the calibration system 1, the processor 12 includes at least one type of core, such as a central processing unit (CPU), a graphics processing unit (GPU), or a reduced instruction set computer (RISC)-CPU. The processor 12 executes a plurality of instructions included in a calibration program stored in the memory 11 in order to calibrate the characteristic parameters Pc of the infrared camera 3 mounted on the host vehicle 2. In this way, the calibration system 1 constructs a plurality of functional blocks for calibrating the characteristic parameters Pc of the infrared camera 3 mounted on the host vehicle 2. The plurality of functional blocks constructed in the calibration system 1 include an image acquisition block 100 and a calibration block 110, as shown in FIG. 2 .

[0026] By cooperation of these blocks 100 and 110, an external calibration method for calibrating the external parameter Pco among the characteristic parameters Pc of the infrared camera 3 mounted on the host vehicle 2 is executed according to the external calibration flow shown in Fig. 4. The external calibration flow is executed in response to a start input from the operator to the input unit 6 while both the calibration system 1 and the host vehicle 2 are running, with a start request for external calibration displayed on the display unit 5. Note that each "S" in the external calibration flow represents a step executed by a plurality of commands included in the external calibration program stored in the memory 11.

[0027] In S10, the image acquisition block 100 acquires a target image Iit as an infrared image Ii by causing the infrared camera 3 to capture an image of the target unit 7 in response to the output command Oi. To this end, as shown in FIG. 5 , the target unit 7 is placed together with the host vehicle 2 in an indoor space (preferably a closed space) 9 with a light source arranged above in a calibration facility where the calibration system 1 is installed. In particular, for calibration of the external parameter Pco, an odd number of target units 7 are placed spaced apart from each other along the left-right direction of the host vehicle 2 equipped with the infrared camera 3. At this time, the front unit 7a as the target unit 7 located in the center in the left-right direction is fixedly positioned, spaced apart from the host vehicle 2 in the fore-and-aft direction and directly facing the host vehicle 2 on the optical axis of the lens system 32.

[0028] The image acquisition block 100 in S10 controls the temperature difference ΔT between the high emissivity area 70 and the low emissivity area 71 in each target unit 7 arranged in this manner so that the high emissivity area 70 is hotter than the low emissivity area 71. Therefore, in the first embodiment, the high emissivity area 70 of the target area 72 is heated higher than the environmental temperature in the indoor space 9, and thereby managed to be at a temperature higher than the environmental temperature. In contrast, the low emissivity area 71 of the target area 72 is cooled lower than the environmental temperature in the indoor space 9, and thereby managed to be at a temperature lower than the environmental temperature. By separately managing the temperatures of these areas 70, 71, the temperature difference ΔT may be controlled to, for example, 10°C, preferably 20°C, and more preferably 30°C.

[0029] In this way, in S10, the infrared camera 3 photographs each target unit 7 in which the temperature difference ΔT between the high emissivity area 70 and the low emissivity area 71 has been controlled. As a result, a target image Iit that captures all of the target units 7 is acquired, as shown in Fig. 6 (however, this figure shows the image Iit of only the front unit 7a).

[0030] 4, the calibration block 110 extracts the feature point coordinates Cp of each of the multiple target areas 72 appearing in the target image Iit acquired in S10. As a result, the calibration block 110 in S11 calibrates the external parameter Pco in accordance with the relative positional relationship between the feature point coordinates Cp extracted for each target area 72.

[0031] Specifically, in S11, the calibration block 110 binarizes the infrared luminance of each of the high emissivity areas 70 and the low emissivity areas 71 in the target image Iit. At this time, in the high emissivity area 70, infrared luminance exceeding the luminance threshold is forcibly converted to a high-side fixed value exceeding the luminance threshold, such as a maximum luminance value, while in the low emissivity area 71, infrared luminance below the luminance threshold is forcibly converted to a low-side fixed value below the luminance threshold, such as a minimum luminance value. Therefore, in S11, the calibration block 110 further extracts, in the first embodiment, grid point coordinates from the binarized high emissivity area 70 and low emissivity area 71 as feature point coordinates Cp for each target area 72 shown in the target image Iit, as shown in FIG. 7 .

[0032] Furthermore, in S11, the calibration block 110 recognizes the amount of deviation that has occurred in the center point of the front unit 7a reflected in the target image Iit, with respect to the central pixel in the target image Iit that is located on the optical axis of the lens system 32, based on the relative positional relationship between the extracted feature point coordinates Cp. At the same time, the calibration block 110 in S11 also recognizes the roll angle that has occurred in the virtual line connecting the center points of the target units 7 reflected in the target image Iit, with respect to the horizontal direction of the target image Iit, based on the relative positional relationship between the extracted feature point coordinates Cp.

[0033] In S11, the calibration block 110 calibrates the external parameters Pco in accordance with the displacement amount and roll angle recognized in this manner. As a result, calibration data Dc representing the calibrated external parameters Pco is output to the host vehicle 2 and stored in the memory 30, making it possible to provide the external parameters Pco for correcting the infrared image Ii acquired by the infrared camera 3. Here, the calibration data Dc representing the calibrated internal parameters Pci may be displayed to the operator by the display unit 5. Note that completion of S11 marks the end of the current execution of the external calibration flow.

[0034] The internal calibration method for calibrating the internal parameters Pci of the characteristic parameters Pc with respect to the external parameters Pco described above by the blocks 100 and 110 jointly is executed according to the internal calibration flow shown in Fig. 8. The internal calibration flow is executed in response to a start input from the operator to the input unit 6 while both the calibration system 1 and the host vehicle 2 are running, with a start request for internal calibration displayed on the display unit 5. Note that each "S" in the internal calibration flow represents a step executed by a plurality of commands included in the internal calibration program stored in the memory 11.

[0035] In S20, the image acquisition block 100 acquires a target image Iit as an infrared image Ii by causing the infrared camera 3 to capture an image of the target unit 7 in response to an output command Oi. To this end, as shown in FIG. 9 , the target unit 7 is placed together with the host vehicle 2 in an interior space (preferably a closed space) 9 that is the same as or different from that in S10. However, in the calibration of the internal parameters Pci, a single target unit 7 is placed spaced apart in the front-to-rear direction from the host vehicle 2 equipped with the infrared camera 3. However, image capture is repeated each time the relative positional state of the target unit 7 and the host vehicle 2 is switched so that the imaging direction from the center of the field of view of the infrared camera 3 toward the center point of the target unit 7 can be variably adjusted in multiple directions.

[0036] The image acquisition block 100 in S20 controls the temperature difference ΔT between the high emissivity area 70 and the low emissivity area 71 in the target unit 7 whose relative arrangement state is switched in this manner so that the high emissivity area 70 is hotter than the low emissivity area 71. Therefore, in the first embodiment, the temperature difference ΔT is controlled by heating the high emissivity area 70 to a temperature higher than the environmental temperature in the indoor space 9 and cooling the low emissivity area 71 to a temperature lower than the environmental temperature in the indoor space 9, as in the case of S10.

[0037] In this way, in S20, the infrared camera 3 repeatedly captures images of each target unit 7, for which the temperature difference ΔT between the high emissivity area 70 and the low emissivity area 71 has been controlled, each time the imaging direction is switched. As a result, a plurality of target images Iit, each of which captures the target unit 7 for each imaging direction, are acquired, as shown in Fig. 10 (however, this figure shows only images Iit from the front imaging direction along the optical axis of the lens system 32).

[0038] 8, the calibration block 110 extracts the feature point coordinates Cp of each of the target areas 72 appearing in each of the target images Iit acquired in S20. As a result, the calibration block 110 in S21 calibrates the internal parameters Pci in accordance with the relative positional relationship between the feature point coordinates Cp extracted for each target area 72 in each target image Iit.

[0039] Specifically, in S21, the calibration block 110 binarizes the infrared luminance of each of the high emissivity areas 70 and the low emissivity areas 71 in each target image Iit, in the same manner as in S11. Further, in S21, the calibration block 110 extracts lattice point coordinates from each of the binarized high emissivity areas 70 and low emissivity areas 71 as feature point coordinates Cp for each target area 72 shown in each target image Iit, as shown in FIG.

[0040] Furthermore, in S21, the calibration block 110 calibrates the internal parameters Pci by nonlinear optimization processing based on the relative positional relationships between the feature point coordinates Cp extracted from each target image Iit in this manner. As a result, calibration data Dc representing the calibrated internal parameters Pci is output to the host vehicle 2 and stored in the memory 30, making it possible to provide the internal parameters Pci for correcting the infrared image Ii acquired by the infrared camera 3. Here, the calibration data Dc representing the calibrated internal parameters Pci may be displayed to the operator by the display unit 5. Note that completion of S21 marks the end of the current execution of the internal calibration flow.

[0041] (Operations and Effects) Operations and effects of the first embodiment described above will be described below.

[0042] In the first embodiment, a target unit 7 in which both high emissivity areas 70 and low emissivity areas 71 adjacent to each other with a difference in emissivity are two-dimensionally arranged as target areas 72 is photographed by an infrared camera 3 mounted on a host vehicle 2. Then, by extracting the feature point coordinates Cp of the multiple target areas 72 that appear in the target image Iit acquired by photographing, the characteristic parameter Pc is calibrated according to the relative positional relationship between the feature point coordinates Cp for each target area 72.

[0043] Here, the target unit 7 according to the first embodiment is photographed by the infrared camera 3 and appears in the target image Iit in a state in which the temperature difference ΔT between the high emissivity area 70 and the low emissivity area 71 is controlled so that the high emissivity area 70 is at a higher temperature than the low emissivity area 71. This allows a contrast in infrared brightness to be imparted to the boundary depicted in the target image Iit between the high emissivity area 70 and the low emissivity area 71, where a radiation energy difference can be ensured based on the controlled temperature difference ΔT. This makes it possible to improve the accuracy of extraction of the feature point coordinates Cp for each target area 72, the boundary of which can be accurately distinguished as both the high emissivity area 70 and the low emissivity area 71, and ultimately the accuracy of calibration of the characteristic parameter Pc.

[0044] In the target unit 7 according to the first embodiment, the temperature difference ΔT between the high emissivity area 70, which serves as the target area 72 and is heated above the ambient temperature, and the low emissivity area 71, which serves as the target area 72 and is cooled below the ambient temperature, is controlled. This makes it possible to emphasize the contrast in infrared luminance at the boundary shown in the target image Iit between the high emissivity area 70 and the low emissivity area 71, which can generate as large a radiation energy difference as possible due to the controlled temperature difference ΔT. This makes it possible to ensure high accuracy in extraction of the feature point coordinates Cp for each target area 72, and therefore high accuracy in calibration of the characteristic parameter Pc.

[0045] According to the first embodiment, feature point coordinates Cp for each target area 72 are extracted from the target image Iit in which the infrared luminance of each of the high emissivity area 70 and the low emissivity area 71 has been binarized. This allows a clear difference in infrared luminance after binarization to be imparted as contrast to the boundary shown in the target image Iit between the high emissivity area 70 and the low emissivity area 71, coupled with the difference in radiation energy due to the controlled temperature difference ΔT. This makes it possible to ensure high accuracy in extracting the feature point coordinates Cp for each target area 72, and therefore high accuracy in calibrating the characteristic parameter Pc.

[0046] According to the first embodiment, the high-emissivity areas 70 and the low-emissivity areas 71 are two-dimensionally arranged in a checkerboard pattern, and the target unit 7 is photographed by the infrared camera 3, so that the target image Iit can be acquired in a photographed state that captures the lattice points of these areas 70 and 71. This makes it easier to accurately extract lattice point coordinates as the feature point coordinates Cp for each target area 72 in the target image Iit. Therefore, it is possible to improve the accuracy of the calibration of the characteristic parameters Pc, which are calibrated according to the relative positional relationships between the lattice point coordinates that form the feature point coordinates Cp for each target area 72.

[0047] 12 , the second embodiment is a modification of the first embodiment. In a target unit 2007 of the second embodiment, the plurality of cooling elements 74 are omitted. Therefore, in S10 and S20 of the second embodiment, the high-emissivity area 70 is heated by the corresponding heating element 73 to a temperature higher than the ambient temperature in the indoor space 9, while the low-emissivity area 71 is left exposed to the ambient temperature in the indoor space 9, thereby controlling the temperature difference ΔT between the areas 70 and 71 that make up the target area 72.

[0048] In the second embodiment, even if temperature management of the low-emissivity area 71 is omitted, the temperature difference ΔT can be controlled by temperature management of heating the high-emissivity area 70 serving as the target area 72, thereby ensuring a difference in radiant energy between the areas 70 and 71. This allows a contrast in infrared brightness to be imparted to the boundary between the areas 70 and 71 as seen in the target image Iit. Therefore, while simplifying the configuration of the target unit 2007, it is possible to ensure the accuracy of extraction of the feature point coordinates Cp for each target area 72, and therefore the accuracy of calibration of the characteristic parameter Pc. Note that, apart from the target and temperature management of the target area 72, the same effects as those of the first embodiment can be achieved.

[0049] 13 , the third embodiment is a modification of the second embodiment. A target unit 3007 of the third embodiment has a background formed around each of a plurality of high emissivity areas 3070, thereby having low emissivity areas 3071 adjacent to each of the high emissivity areas 3070. Here, in the third embodiment, only the high emissivity areas 3070 that can be heated by the heating elements 73 are two-dimensionally arranged in rows and columns as circular target areas 72.

[0050] 14 (S21 in the figure), the coordinates of the center point of the circular contour are extracted from the binarized high emissivity area 3070 as the feature point coordinates Cp for each target area 72 shown in the target image Iit. This third embodiment also makes it possible to achieve the same effects as the second embodiment.

[0051] 15 , the fourth embodiment is a modification of the second and third embodiments. Similar to the third embodiment, the target unit 4007 of the fourth embodiment has a background shape surrounding each of a plurality of high emissivity areas 4070, thereby including a low emissivity area 3071 adjacent to each of the high emissivity areas 4070. However, unlike the third embodiment, the fourth embodiment has only the high emissivity areas 4070 that can be heated by the heating elements 73 two-dimensionally arranged vertically and horizontally as cross-shaped target areas 72.

[0052] 16 (S21 in the figure), the coordinates of the center point of the cross-shaped outline are extracted from the binarized high-emissivity area 4070 as the feature point coordinates Cp for each target area 72 shown in the target image Iit. This fourth embodiment also makes it possible to achieve the same effects as the second embodiment.

[0053] 17 , the fifth embodiment is a modification of the second to fourth embodiments. Similar to the third and fourth embodiments, the target unit 5007 of the fifth embodiment has a background shape surrounding each of a plurality of high emissivity areas 5070, thereby including a low emissivity area 3071 adjacent to each of the high emissivity areas 5070. However, unlike the third and fourth embodiments, the fifth embodiment is different from the third and fourth embodiments in that only the high emissivity areas 5070 that can be heated by the heating elements 73 are two-dimensionally arranged vertically and horizontally as X-shaped target areas 5072 that cross in two directions inclined relative to the vertical and horizontal directions.

[0054] 18 (for S21), the coordinates of the center point of the X-shaped contour are extracted from the binarized high-emissivity area 5070 as the feature point coordinates Cp for each target area 5072 shown in the target image Iit. This fifth embodiment also makes it possible to achieve the same effects as the second embodiment.

[0055] (Other Embodiments) Although multiple embodiments have been described above, the present disclosure should not be construed as being limited to those embodiments, and can be applied to various embodiments and combinations within the scope that does not deviate from the gist of the present disclosure.

[0056] In a modified example, the dedicated computer constituting the calibration system 1 may have at least one of a digital circuit and an analog circuit as a processor. Here, the digital circuit is at least one of an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a system on a chip (SOC), a programmable gate array (PGA), and a complex programmable logic device (CPLD). Furthermore, such a digital circuit may have a memory that stores a program.

[0057] In a modified example, the relationship between the high emissivity areas 3070, 4070, 5070 and the low emissivity area 3071 may be reversed in the third to fifth embodiments. In this case, the plurality of low emissivity areas 3071 that constitute the target areas 3072, 4072, 5072 may be cooled to a temperature lower than the ambient temperature in the indoor space 9 by the corresponding cooling elements 74, while the high emissivity areas 3070, 4070, 5070 may be left exposed to the ambient temperature in the indoor space 9.

[0058] 19 , each of the areas 70, 71 of the first embodiment may be formed in a circular shape similar to the high emissivity area 3070 of the third embodiment, and a background low emissivity area 3071 may be further formed to surround each of the circular areas 70, 71. In this case, the boundary between the low emissivity areas 71, 3071 may be made of the same material as the surface of the high emissivity area 70, or may be made of a heat insulating material, etc.

[0059] In S10 and S20 of the modified example, target units 7, 2007, 3007, 4007, and 5007 may be photographed in an arrangement state different from that described in the first embodiment. In this case, in S11 and S21, the parameters Pco and Pci may be calibrated from the relative positional relationship between the feature point coordinates Cp by a processing method different from that described in the first embodiment.

[0060] In the modified example, the binarization process may be omitted in S11 and S21. In the modified example, the host vehicle 2 to which the calibration system 1 is applied may be, for example, an autonomous robot capable of transporting luggage or collecting information by autonomous or remote driving. The calibration system 1 in the modified example does not include at least the target unit 7 among the constituent units 5 to 7, and in this case, the target unit 7 may be constructed as an external unit of the calibration system 1.

[0061] In addition to the forms described so far, the above-described embodiments and modified examples may be implemented in the form of a processing circuit (e.g., a processing ECU, etc.) or a semiconductor device (e.g., a semiconductor chip, etc.) as a calibration system 1 that is configured to be mountable on a host vehicle 2 and has at least one processor 12 and one memory 11. In this case, the calibration system 1 does not include the constituent units 5 to 7, and the target unit 7 in particular may be constructed as an external unit of the calibration system 1.

[0062] (Additional Remarks) This specification discloses the following technical ideas and their combinations. Note that the reference symbols in parentheses in this Additional Remarks section indicate the correspondence with the specific means described in the above detailed embodiments, and do not limit the technical scope of the present disclosure.

[0063] (Technical Idea 1) A calibration system for calibrating a characteristic parameter (Pc) of an infrared camera (3) mounted on a vehicle (2), the system having a processor (12), is configured to: acquire a target image (Iit) by photographing, with the infrared camera, a target unit (7, 2007, 3007, 4007, 5007) in which at least one of a high emissivity area (70, 3070, 4070, 5070) and a low emissivity area (71, 3071) adjacent to each other with a difference in emissivity height is two-dimensionally arranged as a target area (72); and extract feature point coordinates (Cp) of a plurality of the target areas captured in the target image, thereby calibrating the characteristic parameter in accordance with a relative positional relationship between the feature point coordinates for each of the target areas, wherein the acquisition of the target image is performed by: a target unit in which the temperature difference (ΔT) between the high emissivity area and the low emissivity area is controlled so that the high emissivity area is hotter than the low emissivity area, and the target image is acquired by photographing the target unit with the infrared camera.

[0064] (Technical Idea 2) The calibration system described in Technical Idea 1 includes acquiring the target image by photographing the target unit with the infrared camera, in which the temperature difference between the high emissivity area, which serves as the target area and is heated above the ambient temperature, and the low emissivity area, which serves as the target area and is cooled below the ambient temperature, is controlled.

[0065] (Technical Idea 3) The calibration system described in Technical Idea 1 includes acquiring the target image by photographing the target unit, in which the temperature difference between the high emissivity area that heats up more than the ambient temperature as the target area and the low emissivity area that is exposed to the ambient temperature, is controlled, using the infrared camera.

[0066] (Technical Idea 4) A calibration system according to any one of Technical Ideas 1 to 3, wherein the calibration of the characteristic parameters includes extracting the feature point coordinates for each target area from the target image in which the infrared luminance of each of the high emissivity area and the low emissivity area has been binarized, and calibrating the characteristic parameters in accordance with the relative positional relationship between the feature point coordinates.

[0067] (Technical Idea 5) A calibration system according to any one of Technical Ideas 1 to 4, wherein acquiring the target image includes acquiring the target image by photographing the target unit, in which the high emissivity areas and the low emissivity areas are two-dimensionally arranged in a checkerboard pattern, using the infrared camera; and calibrating the characteristic parameters includes extracting, as the feature point coordinates, grid point coordinates of the target areas that appear in the target image, and thereby calibrating the characteristic parameters according to the relative positional relationships between these grid point coordinates.

[0068] The above-mentioned technical concepts 1 to 5 may be understood as the respective technical concepts of the method and the program.

Claims

1. A calibration system having a processor (12) for calibrating a characteristic parameter (Pc) of an infrared camera (3) mounted on a vehicle (2), configured to: acquire a target image (Iit) by photographing, with the infrared camera, a target unit (7, 2007, 3007, 4007, 5007) in which at least one of a high emissivity area (70, 3070, 4070, 5070) and a low emissivity area (71, 3071) adjacent to each other with a difference in emissivity height is two-dimensionally arranged as a target area (72); and extract feature point coordinates (Cp) of the target areas shown in the target image, thereby calibrating the characteristic parameter in accordance with the relative positional relationship between the feature point coordinates for each target area, wherein the acquisition of the target image is performed by: a target unit in which the temperature difference (ΔT) between the high emissivity area and the low emissivity area is controlled so that the high emissivity area is hotter than the low emissivity area, and the target image is acquired by photographing the target unit with the infrared camera.

2. The calibration system of claim 1, wherein the acquisition of the target image includes acquiring the target image by photographing the target unit with the infrared camera, the target unit controlling the temperature difference between the high emissivity area, which serves as the target area and is heated above ambient temperature, and the low emissivity area, which serves as the target area and is cooled below ambient temperature.

3. The calibration system of claim 1, wherein the acquisition of the target image includes acquiring the target image by photographing the target unit with the infrared camera, in which the temperature difference between the high emissivity area that heats up more than the ambient temperature as the target area and the low emissivity area that is exposed to the ambient temperature is controlled.

4. A calibration system according to any one of claims 1 to 3, wherein the calibration of the characteristic parameters includes extracting the feature point coordinates for each target area from the target image in which the infrared luminance of each of the high emissivity area and the low emissivity area has been binarized, and calibrating the characteristic parameters in accordance with the relative positional relationship between the feature point coordinates.

5. A calibration system according to any one of claims 1 to 3, wherein acquiring the target image includes acquiring the target image by photographing the target unit, in which the high emissivity areas and the low emissivity areas are arranged two-dimensionally in a checkerboard pattern, with the infrared camera, and calibrating the characteristic parameters includes extracting the grid point coordinates of the target areas shown in the target image as the feature point coordinates, and thereby calibrating the characteristic parameters in accordance with the relative positional relationships between those grid point coordinates.

6. A calibration method executed by a processor (12) for calibrating a characteristic parameter (Pc) of an infrared camera (3) mounted on a vehicle (2), comprising: acquiring a target image (Iit) by photographing, with the infrared camera, a target unit (7, 2007, 3007, 4007, 5007) in which at least one of a high emissivity area (70, 3070, 4070, 5070) and a low emissivity area (71, 3071) adjacent to each other with a difference in emissivity height is two-dimensionally arranged as a target area (72); and calibrating the characteristic parameter in accordance with the relative positional relationship between the feature point coordinates for each target area by extracting feature point coordinates (Cp) of the target areas shown in the target image, wherein the acquisition of the target image is a temperature difference (ΔT) between the high emissivity area and the low emissivity area is controlled so that the high emissivity area is hotter than the low emissivity area, and the target image is obtained by photographing the target unit with the infrared camera.

7. A calibration program stored in a storage medium (11) for calibrating characteristic parameters (Pc) of an infrared camera (3) mounted on a vehicle (2), the calibration program including instructions for causing a processor (12) to execute the calibration, the program including instructions for executing the following: acquiring a target image (Iit) by photographing, with the infrared camera, target units (7, 2007, 3007, 4007, 5007) in which at least one of high emissivity areas (70, 3070, 4070, 5070) and low emissivity areas (71, 3071) adjacent to each other with a difference in emissivity height is two-dimensionally arranged as a target area (72); and calibrating the characteristic parameters in accordance with the relative positional relationship between the feature point coordinates for each target area by extracting feature point coordinates (Cp) of the target areas captured in the target image, the acquisition of the target image including the instructions for executing the following: a calibration program including: acquiring the target image by photographing the target unit with the infrared camera, the target unit having a temperature difference (ΔT) between the high emissivity area and the low emissivity area controlled so that the high emissivity area is hotter than the low emissivity area.

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