Marker

Abstract

This marker is for imaging using a thermal camera and is formed from a thermally conductive material. The surface of the marker comprises a pattern formed by a first surface region SA1 and a second surface region SA2, wherein the emissivity of the second surface region SA2 is higher than the emissivity of the first surface region SA1.

Description

Marker

[0001] The disclosed technology relates to a technology for realizing a marker that can be photographed by a thermal camera without requiring a power source.

[0002] Non-patent document 1 describes a marker that can be photographed with a thermal camera. The marker in Non-patent document 1 has a two-dimensional pattern made of foam-coated aluminum foil attached to the back of the garment. When this garment is worn on a human body and photographed with a thermal camera, the area with the foam-coated aluminum foil on the back blocks the heat radiated by the human body, resulting in an image of a temperature close to the ambient temperature. The area without the foam-coated aluminum foil on the back does not block the heat radiated by the human body, resulting in an image of a temperature close to body temperature. This allows the thermal camera to photograph the two-dimensional pattern.

[0003] Kitahara Itaru and four others, "Thermal-ID: A personal authentication method using human body heat," [online], 2005, [Retrieved August 2, 2022], Internet <URL: http: / / www.interaction-ipsj.org / archives / paper2005 / pdf2005 / interactive / A114.pdf>

[0004] In Non-Patent Document 1, a marker that can be photographed with a thermal camera is realized without a power source. However, there is a problem in that the pattern cannot be photographed unless the marker is in contact with an object whose temperature is different from the ambient temperature, such as a human body, at the time of photographing. Furthermore, even if the marker is in contact with an object whose temperature is different from the ambient temperature at the time of photographing, there is a problem in that the accuracy of photographing the pattern decreases if the temperature of the surface of the object being photographed is significantly uneven.

[0005] The purpose of the disclosed technology is to provide a marker that can capture a pattern even if it is not in contact with something whose temperature is different from the ambient temperature at the time of capture, and that does not significantly reduce the accuracy of capturing the pattern even if there is a large temperature variation on the surface of something that is in contact with it at the time of capture.

[0006] One aspect of the disclosed technology is a marker for being photographed by a thermal camera, the marker being formed from a highly thermally conductive material, the surface of the marker including a pattern consisting of a first surface region and a second surface region, and the emissivity of the second surface region being higher than the emissivity of the first surface region.

[0007] According to the disclosed technology, it is possible to photograph a pattern even if the pattern is not in contact with an object whose temperature is different from the ambient temperature at the time of photographing, and the accuracy of photographing the pattern does not decrease significantly even if the temperature of the surface of an object in contact with the pattern at the time of photographing is significantly uneven.

[0008] FIG. 1A is a plan view of an example of a marker. FIG. 1B is an α-α cross-sectional view of the marker in FIG. 1A. FIG. 2A is a plan view of an example of a marker. FIG. 2B is a β-β cross-sectional view of the marker in FIG. 2A. FIG. 3A is a plan view of an example of a marker. FIG. 3B is a γ-γ cross-sectional view of the marker in FIG. 3A. FIG. 4 is a diagram showing an example of the functional configuration of a marker detection device 3. FIG. 5 is a diagram showing an example of a processing procedure of a marker detection method. FIG. 6 is a diagram showing an example of the functional configuration of a computer.

[0009] Hereinafter, embodiments of the disclosed technology will be described with reference to the drawings. Note that components having the same functions in the drawings are given the same reference numerals, and redundant description will be omitted.

[0010] 1A and 1B are diagrams showing examples of markers. Fig. 1A is a plan view of the example marker. Fig. 1B is an α-α cross-sectional view of the marker in Fig. 1A.

[0011] The marker comprises a first material 1 and a second material 2.

[0012] The marker is made of a highly thermally conductive material. That is, both the first material 1 and the second material 2 are made of highly thermally conductive materials. Note that a highly thermally conductive material is a material with high thermal conductivity, for example, a material with a thermal conductivity of 10 W / mK or higher. The highly thermally conductive materials used for the first material 1 and the second material 2 are appropriately selected from materials with a thermal conductivity of 10 W / mK or higher depending on the application and size.

[0013] The first material 1 and the second material 2 are made of highly thermally conductive materials with different emissivities. The emissivity of the material with the higher emissivity between the first material 1 and the second material 2 may be approximately 1. For example, the emissivity of the first material 1 is lower than that of the second material 2. In other words, the emissivity of the second material 2 is higher than that of the first material 1. If the marker is formed so that the emissivity of the first material 1 is lower than that of the second material 2, examples of the first material 1 are metals such as copper, aluminum, zinc, gold, silver, and duralumin, and examples of the second material 2 are black body paint, silicon nitride, and carbon graphite.

[0014] The reason why the marker is formed from a highly thermally conductive material is that it is preferable for the marker to have as uniform a temperature as possible, for example, to facilitate the process of detecting the marker from a thermal image obtained by heating or cooling the marker and then photographing it with a thermal camera, as described below, or to facilitate the process of detecting the marker from a thermal image obtained by photographing a marker in contact with an object with a large surface temperature variation with a thermal camera. To ensure that the marker reaches a uniform temperature in a short time, for example, the first material 1 and the second material 2 should be made of a highly thermally conductive material with a thermal conductivity of 100 W / mK or higher. Furthermore, to ensure that the marker reaches a uniform temperature even with a small amount of heat, it is preferable that the thickness of the marker (i.e., the thickness of the first material 1 and the second material 2) be thin. On the other hand, to minimize the temperature change between heating or cooling the marker and photographing it with a thermal camera, it is preferable that the volume of the marker (i.e., the volume of the first material 1 and the volume of the second material 2) be large. Taking the above factors into consideration, the first material 1 and the second material 2 of the marker should have a predetermined thickness and size. The predetermined thickness and size are appropriately determined through experiments or the like so as to obtain the desired results.

[0015] By attaching the second material 2 to a partial region on one side of the plate-shaped first material 1 serving as the base material, a pattern is formed on the surface of the marker by an area where the surface of the first material 1 is exposed and an area where the surface of the second material 2 is exposed. An example of the pattern formed on the surface of the marker is a pattern used in an AR marker. For an example of a pattern used in an AR marker, see Reference 1. The pattern formed on the surface of the marker may be a predetermined one-dimensional barcode, a predetermined two-dimensional barcode, or any predetermined pattern.

[0016] (Reference 1) Kato, H., Billinghurst, M. "Marker tracking and HMD calibration for a video-based augmented reality conferencing system." In Proceedings of the 2nd IEEE and ACM International Workshop on Augmented Reality (IWAR 99), October 1999. Note that since the markers are detected from thermal images captured by a thermal camera, the marker patterns do not need to be visible. In other words, the marker patterns may be made inconspicuous in the wavelength range of visible light. This allows the markers to be invisible markers whose patterns are inconspicuous to the human eye. For example, by using materials of similar colors for the first material 1 and the second material 2, the patterns can be made inconspicuous in the wavelength range of visible light.

[0017] Conversely, the pattern of the marker may be made conspicuous in the wavelength range of visible light. That is, the brightness and / or color of the surface of the first material 1 and the surface of the second material 2 may be made significantly different from each other. In this way, the marker can be easily identified visually by a person and can also be used as a visible marker. When the marker is also used as a visible marker, the first material 1 and the second material 2 may be made of materials that are different from each other in brightness and / or color.

[0018] As shown in FIG. 1B, the surface of the marker includes a pattern with a first surface area SA1 and a second surface area SA2.

[0019] Here, as shown in FIG. 1B, the partial area of ​​the marker whose surface is the first surface area SA1 will be referred to as the first partial area PA1, and the partial area of ​​the marker whose surface is the second surface area SA2 will be referred to as the second partial area PA2.

[0020] When the first partial area PA1 and the second partial area PA2 are defined in this way, the following can be said.

[0021] The first material 1 is a single base material that is continuous with the first partial region PA1 and the second partial region PA2. In the first partial region PA1, the surface of the first material 1 is defined as a first surface region SA1. The second partial region PA2 has the first material 1 and a second material 2 formed on the surface of the first material 1. In the second partial region PA2, the surface of the second material 2 is defined as a second surface region SA2. The emissivity of the second surface region SA2 is higher than the emissivity of the first surface region SA1.

[0022] <<Marker Variation Example 1>> As described above, the first material 1 and the second material 2 only need to have different emissivities, so the relationship between the emissivity of the first material 1 and the emissivity of the second material 2 may be reversed from the example described above.

[0023] That is, the plate-shaped first material 1 serving as the substrate may be a highly thermally conductive material (e.g., black paint, silicon nitride, carbon graphite) having a higher emissivity than the second material 2, and the second material 2 may be a highly thermally conductive material (e.g., metals such as copper, aluminum, zinc, gold, silver, duralumin, etc.) having a lower emissivity than the first material 1.

[0024] An example of the marker in this case is shown in Figures 2A and 2B, where Figure 2A is a plan view of the example marker, and Figure 2B is a β-β cross-sectional view of the marker in Figure 2A.

[0025] As with the marker described above, a second material 2 is attached to a partial area on one side of a plate-shaped first material 1 that serves as the base material, thereby forming a pattern on the surface of the marker consisting of areas where the surface of the first material 1 is exposed and areas where the surface of the second material 2 is exposed.

[0026] As shown in FIG. 2B, the surface of the marker includes a pattern of a first surface area SA1 and a second surface area SA2.

[0027] Here, as shown in FIG. 2B, the partial area of ​​the marker whose surface is the first surface area SA1 will be referred to as the first partial area PA1, and the partial area of ​​the marker whose surface is the second surface area SA2 will be referred to as the second partial area PA2.

[0028] When the first partial area PA1 and the second partial area PA2 are defined in this way, the following can be said.

[0029] The first material 1 is a single base material that is continuous with the first partial region PA1 and the second partial region PA2. In the second partial region PA2, the surface of the first material 1 is defined as the second surface region SA2. The first partial region PA1 has the first material 1 and the second material 2 formed on the surface of the first material 1. In the first partial region PA1, the surface of the second material 2 is defined as the first surface region SA1. The emissivity of the second surface region SA2 is higher than the emissivity of the first surface region SA1.

[0030] <<Marker Variation 2>> The marker may be formed only from a first material 1 (such as a metal as copper, aluminum, zinc, gold, silver, duralumin, etc.) which is a highly thermally conductive material.

[0031] An example of the marker in this case is shown in Figures 3A and 3B, where Figure 3A is a plan view of the example marker, and Figure 3B is a γ-γ cross-sectional view of the marker in Figure 3A.

[0032] A surface treatment is applied to a portion of one surface of the plate-shaped first material 1 serving as the substrate, thereby forming a pattern on the surface of the marker consisting of an area where the surface of the first material 1 is not surface-treated and an area where the surface of the first material 1 is surface-treated. Alternatively, a first surface treatment is applied to a portion of one surface of the plate-shaped first material 1 serving as the substrate, and a second surface treatment different from the first surface treatment is applied to an area other than the portion of the one surface of the first material 1, thereby forming a pattern on the surface of the marker consisting of an area where the first surface treatment is applied to the surface of the first material 1 and an area where the second surface treatment is applied to the surface of the first material 1. The surface treatment may be a geometric treatment that changes the fine shape of the surface, or a treatment that chemically changes the surface. Examples of surface treatments include polishing such as mirror finishing, polishing, and rough polishing, and oxidation.

[0033] Here, as shown in FIG. 3B, the partial area of ​​the marker whose surface is the first surface area SA1 will be referred to as the first partial area PA1, and the partial area of ​​the marker whose surface is the second surface area SA2 will be referred to as the second partial area PA2.

[0034] When the first partial area PA1 and the second partial area PA2 are defined in this way, the following can be said.

[0035] The marker has a single substrate (first material 1) made of a highly thermally conductive material that is continuous with the first partial region PA1 and the second partial region PA2. The first surface region SA1 and the second surface region SA2 are both surfaces of the substrate. At least one of the first surface region SA1 and the second surface region SA2 is surface-treated so that the emissivity of the second surface region SA2 is higher than the emissivity of the first surface region SA1. For example, the second surface region SA2 is surface-treated so that it is rougher than the first surface region SA1.

[0036] 1 to 3, the marker is a marker to be photographed by a thermal camera and is made of a highly thermally conductive material. The surface of the marker includes a pattern consisting of a first surface region SA1 and a second surface region SA2, and the emissivity of the second surface region SA2 is higher than the emissivity of the first surface region SA1.

[0037] <Marker principle> Emissivity is the ratio of the light energy emitted by radiation from an object at a certain temperature to the light energy emitted by a black body at the same temperature, taken as 1. When photographed with a thermal camera, the higher the emissivity, the closer a temperature to the object's surface temperature will be reflected in the thermal image obtained by the photograph, and the lower the emissivity, the lower the temperature that is less correlated with the object's surface temperature will be reflected in the thermal image obtained by the photograph. For example, if the emissivity of an object's surface is close to 1, the object's surface temperature will be reflected almost exactly in the thermal image. On the other hand, if the emissivity is 0, when an object is photographed with a thermal camera, the ambient temperature reflected on the object's surface will be reflected in the thermal image.

[0038] Therefore, as described in <Marker Configuration>, for example, the marker is configured so that two types of regions with different emissivity are formed on the surface. In this case, when photographed with a thermal camera, the region with the higher emissivity of the two regions on the marker's surface will reflect a temperature closer to the marker's temperature than the region with the lower emissivity of the two regions on the marker's surface, and the region with the lower emissivity of the two regions on the marker's surface will reflect a temperature closer to the ambient temperature than the region with the higher emissivity of the two regions on the marker's surface.

[0039] If the temperature of the marker is close to the temperature of the surroundings, the temperature difference between the area with higher emissivity and the area with lower emissivity on the marker surface will be small on the thermal image taken by the thermal camera. However, if the temperature difference between the marker and the surroundings is large, the difference in emissivity on the marker surface will appear as a temperature difference on the thermal image taken by the thermal camera.

[0040] Therefore, before capturing images with a thermal camera, the marker is first warmed or cooled. For example, when warming a marker before capturing images with a thermal camera, the marker is warmed by holding, touching, or rubbing it with a hand for about 2 to 3 seconds. For example, when cooling a marker before capturing images with a thermal camera, the marker is cooled by the heat of vaporization by spraying water on it with a spray bottle or wiping it with a wet cloth. For example, a Peltier element is brought into contact with a part of the marker, and an electric current is passed through the Peltier element, thereby warming or cooling the marker. This makes it possible to capture a pattern even if the marker is not in contact with something whose temperature is different from the ambient temperature at the time of capturing the image.

[0041] Alternatively, the thermal camera can capture images with the marker in contact with an object whose temperature differs from the ambient temperature. This prevents significant degradation in the accuracy of capturing the pattern even if the surface temperature of the object being captured varies greatly.

[0042] Alternatively, the thermal camera may capture an image of a marker with a portion of the marker in contact with an object whose temperature differs from the ambient temperature. For example, the marker is captured with a thermal camera with a Peltier element in contact with a portion of the back of the marker and a current flowing through the Peltier element. This allows the pattern to be captured with high accuracy even if only a portion of the marker is in contact with an object whose temperature differs from the ambient temperature at the time of capture.

[0043] <Example of Use of Markers> An example of use of markers will be described with reference to Figures 4 and 5. In this example, marker detection is performed using a marker detection device 3 and method. That is, a system including a marker having the above-described configuration and the marker detection device 3 is a marker detection system.

[0044] 4, the marker detection device 3 includes, for example, a thermal image acquisition unit 32 and a marker detection unit 33. The marker detection device 3 may further include a thermal camera 31.

[0045] The marker detection method is realized, for example, by each component of the marker detection device 3 performing the processes of steps S31 to S33 shown in FIG.

[0046] Before the processing of step S31, the marker is heated or cooled and then attached at a position according to the intended use of the marker. Alternatively, before the processing of step S31, the marker is heated or cooled while attached at a position according to the intended use of the marker. Alternatively, the processing of step S31 is performed after the marker is attached at a position according to the intended use and heated or cooled. Examples of heating and cooling methods are as described above. The intended use of the marker is the same as that of a marker photographed by a conventional visible light camera, and includes identifying the photographing range and location, and identifying the position and attitude of the camera.

[0047] <<Thermal Camera 31>> The thermal camera 31 captures a thermal image, which is an image composed of images acquired from the thermal camera 31 of heat images within a capture range including the position where the marker is attached (step S31). The thermal image captured by the thermal camera 31 is input to the thermal image acquisition unit 32. If the marker is heated or cooled before the processing of step S31, it is preferable that the thermal camera 31 capture the thermal image as soon as possible after the marker is heated or cooled.

[0048] <<Thermal Image Acquisition Unit 32 >> The thermal image acquisition unit 32 acquires a thermal image captured by the thermal camera 31 (step S32). The acquired thermal image is input to the marker detection unit 33.

[0049] <<Marker Detector 33>> The marker detector 33 detects markers using the thermal image (step S33). The marker detection result is output from the marker detector 33.

[0050] An existing marker detection algorithm can be used for the marker detection process by the marker detection unit 33. However, as the marker detection process, the marker detection unit 33 may perform step S331, and then detect the marker using the existing marker detection algorithm in steps S332 and S333, as in the following example.

[0051] An example of the marker detection process performed by the marker detection unit 33 will be described below. In the following description, V1 and V2 are predetermined values ​​that are different from each other. For example, V1 is 0 and V2 is 255.

[0052] The marker detection unit 33 generates a pre-processed thermal image by setting V1 as the pixel value in the thermal image that is equal to or greater than the threshold Th if the marker is heated before being photographed by the thermal camera 31, and by setting V2 as the pixel value in the thermal image that is equal to or less than the threshold Tc if the marker is cooled before being photographed by the thermal camera 31 (step S331).

[0053] If the marker is warmed by hand before being photographed by the thermal camera 31, Th is, for example, 40° C. The process of step S331 can reduce errors in the determination made in the process of step S332, which will be described later.

[0054] The marker detection unit 33 generates a binarized thermal image by binarizing the preprocessed thermal image using the threshold value T (step S332). For example, the marker detection unit 33 generates a binarized thermal image by defining pixel values ​​in the preprocessed thermal image that are equal to or greater than the threshold value T as V2 and pixel values ​​that are less than the threshold value T as V1.

[0055] The marker detection unit 33 determines whether an area consisting of a first pixel value (e.g., V1) and a second pixel value (e.g., V2) that match a pre-registered pattern exists in the binarized thermal image, and if an area that matches the pre-registered pattern exists in the binarized thermal image, the marker detection unit 33 determines that the area that matches the pre-registered pattern is a marker corresponding to the pre-registered pattern (step S333).

[0056] For example, marker detection is performed in this manner.

[0057] <Application Examples of Markers> As described above, markers can be captured by a thermal camera. Furthermore, by appropriately selecting the material of the pattern, the marker can also be captured by a visible light or near-infrared camera. Therefore, the same marker can be used to align the thermal camera with the visible light or near-infrared camera. Conversely, as described above, the pattern may be made inconspicuous in the visible light wavelength range. This allows it to be used in situations where it is desirable to make the marker less conspicuous in the design of furniture, interiors, etc.

[0058] <Programs, Recording Media, etc.> The processing of each unit of the marker detection device 3 may be implemented by a computer. In this case, the processing content of the functions to be possessed by the marker detection device 3 is described by a program. Then, this program is loaded into the storage unit 1020 of the computer 1000 shown in Fig. 6 and operated by the arithmetic processing unit 1010, input unit 1030, output unit 1040, display unit 1060, etc., thereby implementing various processing functions of the marker detection device 3 on the computer.

[0059] The marker detection device 3, as a single hardware entity, includes, for example, an input unit capable of inputting signals from outside the hardware entity, an output unit capable of outputting signals to outside the hardware entity, a communication unit to which a communication device (e.g., a communication cable) capable of communicating with outside the hardware entity can be connected, a CPU (which may also include a central processing unit, cache memory, registers, etc.) as an arithmetic processing unit, RAM and ROM as memories, an external storage device such as a hard disk, and buses connecting these input unit, output unit, communication unit, CPU, RAM, ROM, and external storage device so that data can be exchanged between them. If necessary, the hardware entity may also be provided with a device (drive) capable of reading and writing to a recording medium such as a CD-ROM. An example of a physical entity equipped with such hardware resources is a general-purpose computer.

[0060] The external storage device of the hardware entity stores the programs required to realize the above-mentioned functions and the data required for processing these programs (the programs may be stored in a ROM, which is a read-only storage device, for example, instead of an external storage device). Data obtained by processing these programs is stored in RAM, the external storage device, etc. as appropriate.

[0061] In the hardware entity, each program stored in an external storage device (or ROM, etc.) and the data required to process each program are loaded into memory as needed, and interpreted, executed, and processed by the CPU as appropriate. As a result, the CPU realizes predetermined functions (each component represented as a "... unit" above). In other words, each component of the embodiments of the present invention may be configured by a processing circuitry.

[0062] As described above, when the processing functions of the hardware entity (marker detection device 3) described in the above embodiment are realized by a computer, the processing contents of the functions that the hardware entity should have are described by a program. Then, by executing this program on a computer, the processing functions of the hardware entity are realized on the computer.

[0063] The program describing the processing contents can be recorded on a computer-readable recording medium, such as a non-transitory recording medium, specifically a magnetic recording device, an optical disk, or the like.

[0064] The program may be distributed, for example, by selling, transferring, lending, etc. a portable recording medium such as a DVD or CD-ROM on which the program is recorded. Furthermore, the program may be stored in a storage device of a server computer, and then transferred from the server computer to another computer via a network, thereby distributing the program.

[0065] A computer executing such a program, for example, first stores the program recorded on a portable recording medium or transferred from a server computer in its own non-transitory storage device, auxiliary storage unit 1050. Then, when executing a process, the computer loads the program stored in auxiliary storage unit 1050, its own non-transitory storage device, into storage unit 1020 and executes processing in accordance with the loaded program. Alternatively, as another form of execution of this program, the computer may load the program directly from a portable recording medium into storage unit 1020 and execute processing in accordance with the program. Furthermore, the computer may execute processing in accordance with the received program each time a program is transferred from a server computer to the computer. Alternatively, the server computer may not transfer the program to the computer, but may instead execute the processing function by issuing an execution instruction and obtaining the results, thereby executing the above-described processing through a so-called ASP (Application Service Provider) type service. Note that, in this embodiment, the program includes information used for processing by a computer that is equivalent to a program (e.g., data that is not a direct instruction to the computer but has properties that define computer processing).

[0066] In addition, in this embodiment, the marker detection device 3 is configured by executing a predetermined program on a computer, but at least a part of the processing contents may be realized by hardware.

[0067] It goes without saying that other modifications can be made as appropriate without departing from the spirit of the present invention.

[0068] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

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5. A marker to be photographed by a thermal camera, a surface of the marker including a pattern having a first surface region and a second surface region; a marker having an emissivity of the second surface region greater than an emissivity of the first surface region, The marker is characterized in that it is made of a highly thermally conductive material.

6. The marker of claim 5, A partial region of the marker whose surface is the first surface region is called a first partial region; A partial region of the marker whose surface is the second surface region is called a second partial region, The marker has a first material and a second material made of a highly thermally conductive material; The first material is a substrate that is continuous with the first partial region and the second partial region, In the first partial region, a surface of the first material is defined as the first surface region, The second partial region includes the first material and the second material formed on the surface of the first material, In the second partial region, a surface of the second material is the second surface region, A marker having an emissivity of the second surface region that is greater than the emissivity of the first surface region.

7. The marker of claim 5, A partial region of the marker whose surface is the first surface region is called a first partial region; A partial region of the marker whose surface is the second surface region is called a second partial region, The marker has a first material and a second material made of a highly thermally conductive material; The first material is a substrate that is continuous with the first partial region and the second partial region, In the second partial region, a surface of the first material is the second surface region, The first partial region includes the first material and the second material formed on the surface of the first material, In the first partial region, a surface of the second material is the first surface region, A marker having an emissivity of the second surface region that is higher than the emissivity of the first surface region.

8. The marker of claim 5, A partial region of the marker whose surface is the first surface region is called a first partial region; A partial region of the marker whose surface is the second surface region is called a second partial region, the marker has a substrate made of a highly thermally conductive material that is continuous with the first region and the second region; the first surface region and the second surface region are both surfaces of the substrate; A marker in which either the first surface region or the second surface region is oxidized so that the emissivity of the second surface region is higher than the emissivity of the first surface region.

9. The marker of claim 5, A partial region of the marker whose surface is the first surface region is called a first partial region; A partial region of the marker whose surface is the second surface region is called a second partial region, the marker has a substrate made of a highly thermally conductive material that is continuous with the first region and the second region; the first surface region and the second surface region are both surfaces of the substrate; A marker in which either the first surface region or the second surface region is roughly polished so that the emissivity of the second surface region is higher than the emissivity of the first surface region.

10. The marker of claim 6 or 7, The first material and the second material are made of materials having similar colors. Marker.