JP7614809B2 - Terahertz wave camera system and method for controlling the terahertz wave camera system - Google Patents

Description

The present invention relates to a terahertz wave camera system.

Terahertz waves are radio waves that have any frequency band, typically ranging from 0.2 THz to 30 THz. Terahertz waves have a longer wavelength than visible light or infrared light, making them less susceptible to scattering from the subject and highly penetrating many materials. In addition, terahertz waves have a shorter wavelength than millimeter waves, making it possible to obtain high spatial resolution. Taking advantage of these characteristics, terahertz waves are expected to be applied to safe imaging technology as an alternative to X-rays. For example, they are expected to be applied to body checks in public places and hidden object inspection technology such as surveillance cameras.

Patent Document 1 describes a camera system that uses terahertz waves. In this document, it is described that in an active terahertz wave camera system, terahertz waves are generated from multiple terahertz wave light sources, the terahertz waves are irradiated onto a subject, and the terahertz waves reflected by the subject are detected.

JP 2018-87725 A

When an active terahertz wave camera system is used to capture an image of a subject with a concealed object under a covering, some of the irradiated terahertz waves may be reflected by the covering. As a result, the image obtained may be an image in which information about the concealed object is superimposed with information based on the terahertz waves reflected from an unwanted interface, i.e., noise.

In addition, the surface of the subject has a complex shape, and it differs for each subject. In other words, the subject is composed of a combination of multiple reflective surfaces. Therefore, the positional relationship between the illumination unit, which is the light source, and the detection unit with respect to the reflective surface may change for each reflective surface that constitutes the subject. In addition, when the subject moves, the subject's posture changes from moment to moment, and this posture change may cause the positional relationship between the illumination unit, which is the light source, and the detection unit with respect to the reflective surface that constitutes the subject to change from moment to moment. Due to such changes in positional relationship, undesired reflected terahertz waves from the subject may be incident, resulting in an image with a lot of noise.

Therefore, the present invention aims to obtain terahertz images with reduced noise.

One embodiment of the terahertz wave camera system of the present invention is characterized by having a first transmitter capable of emitting a first terahertz wave, a second transmitter capable of emitting a second terahertz wave arranged at a position different from the first transmitter, a detector capable of detecting at least either the first reflected terahertz wave that is a part of the first terahertz wave reflected from the subject or the second reflected terahertz wave that is a part of the second terahertz wave reflected from the subject and outputting image data based on the detected terahertz wave, and a first controller that controls at least one of the operation of the first transmitter and the operation of the second transmitter under conditions set based on the image data.

The present invention makes it possible to obtain terahertz images with reduced noise.

FIG. 1 is a diagram for explaining the configuration of a terahertz wave camera system according to a first embodiment. FIG. 2A is a diagram for explaining an example of the configuration of a transmission unit according to the first embodiment; FIG. 2B is a diagram for explaining an example of the configuration of a transmission unit according to the first embodiment. 13A is a diagram for explaining an example of the configuration of a transmission unit according to a second embodiment; FIG. 13B is a diagram for explaining an example of the configuration of a transmission unit according to the second embodiment; FIG. 13 is a diagram for explaining the configuration of a terahertz wave camera system according to a third embodiment. FIG. 4 is a diagram for explaining an operation flow of the terahertz wave camera system according to the first embodiment. 3A to 3C are diagrams illustrating terahertz images acquired by the terahertz wave camera system according to the first embodiment. FIG. 11 is a flowchart for explaining an operation flow of the terahertz wave camera system according to the third embodiment. FIG. 13 is a diagram for explaining the configuration of a terahertz wave camera system according to a fourth embodiment. FIG. 2 is a diagram for explaining an example of the arrangement of an image processing unit. FIG. 2A is an image diagram illustrating the terahertz wave camera systems according to the first and third embodiments; FIG. 2B is a schematic diagram illustrating the terahertz wave camera system according to the first embodiment; and FIG. 2C is a diagram illustrating terahertz waves. FIG. 11 is a schematic diagram illustrating a terahertz wave camera system according to a third embodiment. FIG. 4A is a diagram illustrating an operation flow of the terahertz wave camera system according to the first embodiment, and FIG. 4B is a table illustrating conditions. FIG. 4 is a diagram for explaining an operation flow of the terahertz wave camera system according to the first embodiment. FIG. 13 is a diagram for explaining a learning model according to the fifth embodiment. FIG. 13 is a flowchart for explaining an operation flow of the terahertz wave camera system according to the sixth embodiment.

The following embodiments are described in detail with reference to the attached drawings. Note that the present invention is not limited to the following embodiments. Although the embodiments describe multiple features, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicate explanations are omitted.

First, we will explain terahertz waves. Terahertz waves are radio waves that have any frequency band, typically within the range of 0.2 THz to 30 THz. Terahertz waves have a longer wavelength than visible light or infrared light, so they are less susceptible to scattering from the subject and have strong penetrating properties for many materials. Furthermore, terahertz waves have a shorter wavelength than millimeter waves, so they can achieve high spatial resolution. Taking advantage of these characteristics, terahertz waves are expected to be applied to safe imaging technology that replaces X-rays. Specific examples of imaging technology that are expected to be applied include body checks and surveillance cameras in public places. Below, we will explain a terahertz wave camera system that can be applied to body checks and surveillance cameras, which are expected to be applied.

First Embodiment
1 is a diagram illustrating the configuration of a terahertz wave camera system 100 according to this embodiment. The terahertz wave camera system 100 has at least an illumination unit 101, a detection unit 102, a control unit 103, and an image processing unit 105. The terahertz wave camera system 100 may also have a visible camera 109. The illumination unit 101 irradiates a subject 106 with terahertz waves, and the detection unit 102 detects the terahertz waves reflected by the subject 106. The terahertz wave camera system 100 is an active camera system.

The subject 106 is, for example, a person or an object. The subject 106 in this embodiment has at least a concealed object 106a and a covering 106b. The covering 106b covers the object. For example, the covering 106b is something worn by a person, such as clothing or an attachment, that is, something that covers a person. Also, for example, the covering 106b covers an object such as a cardboard box, an envelope, or a packaging material. The concealed object 106a is an object covered by the covering 106b. For example, the concealed object 106a is a dangerous object such as a firearm or an explosive, an ornament or jewelry, or a small device such as a smartphone. For example, the concealed object 106a can be stored inside the covering 106b. In this embodiment, the subject 106 is a person, and is in a state where the concealed object 106a, such as a gun or a knife, is hidden under the covering 106b, which is clothing. However, examples of the subject 106 are not limited to this, and could be, for example, mail that contains a concealed object 106a, such as a weapon or explosive, hidden inside a covering 106b, which is a packaging material such as a cardboard box or an envelope.

The illumination unit 101 has at least a transmitter 101a and a transmitter 101b arranged at a position different from that of the transmitter 101a. The transmitter 101a emits terahertz waves 107a, and the transmitter 101b emits terahertz waves 107b. FIG. 1 shows an example in which the illumination unit 101 has transmitters 101c and 101d in addition to the transmitters 101a and 101b. The number of transmitters that the illumination unit 101 has is not limited to this, and may be one or more. The configuration of the transmitter 101a and the like will be described in detail later. The subject 106 is irradiated with the terahertz waves 107a and 107b.

Here, the band of the terahertz waves used in the illumination unit 101 typically ranges from 0.2 THz to 30 THz. The band of the terahertz waves may have any frequency band, or may be a single frequency. Terahertz waves of 1 THz or less have high transparency even to clothing, which is the assumed covering 106b. And, in order to obtain an image resolution capable of identifying the shape of the concealed object 106a, terahertz waves of 0.3 THz or more are desirable. Therefore, the band of the terahertz waves in this embodiment is a frequency range of 0.2 THz to 30 THz, preferably 0.3 THz to 1 THz.

The detection unit 102 is a terahertz wave camera that acquires a two-dimensional distribution of reflected terahertz waves from the subject 106. Details of the configuration of the detection unit 102 are described in JP 2019-105622 A. The detection unit 102 has a receiving unit 102a that receives terahertz waves. The receiving unit 102a has, for example, a plurality of receiving elements, each of which has sensitivity to terahertz waves. The receiving element has, for example, a Schottky barrier diode and an antenna.

The detection unit 102 detects at least one of the reflected terahertz waves 108a and 108b, and outputs the detected waves as image data. The reflected terahertz waves 108a include at least a portion of the terahertz waves 107a reflected by the subject 106. The reflected terahertz waves 108b include at least a portion of the terahertz waves 107b reflected by the subject 106. The reflected terahertz waves 108a may be reflected waves from a concealed object 106a of the subject 106, and the reflected terahertz waves 108b may be reflected waves from a covering 106b of the subject 106. The receiving unit 102a of this embodiment is mainly capable of receiving and detecting the reflected terahertz waves 108a.

The image processing unit 105 processes the image data output from the detection unit 102 and generates a terahertz image. The image processing unit 105 performs a desired judgment based on the generated terahertz image and outputs the judgment result to the control unit 103. Specifically, the image processing unit 105 is composed of a central processing unit (CPU) and a graphics processing unit (GPU).

The control unit 103 controls the operation of the illumination unit 101 and the detection unit 102. Furthermore, it controls the operation of the illumination unit 101 based on the terahertz image or the judgment result sent from the image processing unit 105. Specifically, it controls the emission units 101a to 101d and changes the terahertz waves 107a to 107d.

Now, the terahertz wave camera system 100 of this embodiment will be described with reference to FIG. 10. As described above, in body checks, surveillance cameras, and the like, it is necessary to photograph a subject and check whether or not the subject is carrying a concealed object (e.g., dangerous objects such as firearms or explosives, ornaments or jewelry, or small devices such as smartphones) under a covering (e.g., clothing, packaging, etc.). Through detailed investigation, the inventors have found that the image acquired in a terahertz wave camera system is an image in which images based on multiple reflected terahertz waves are superimposed.

Electromagnetic waves, including terahertz waves, have the following characteristics. When electromagnetic waves are irradiated onto an uneven structure with a wavelength equal to or smaller than the wavelength, the electromagnetic waves are reflected specularly without being scattered by the surface of the uneven structure. In other words, for a certain electromagnetic wave, an uneven structure smaller than the wavelength can be a mirror surface. For example, the uneven structure of the surface of human skin and the uneven structure of a metal surface are smaller than the wavelength of terahertz waves. Therefore, for terahertz waves, the surface of human skin and the metal surface can be mirror surfaces. In addition, some terahertz waves are transmitted and some are reflected by the cloth materials used in clothing and packaging materials such as cardboard and envelopes. Therefore, when observing a person hiding an object under clothing as a covering using terahertz waves, an image based on the terahertz waves reflected by the clothing, an image based on the terahertz waves reflected by the object, and an image based on the terahertz waves reflected by the person are superimposed.

FIG. 10A is an image diagram illustrating the superposition of multiple terahertz wave reflection images to explain this embodiment. The subject 1092 is assumed to be a person holding an object (e.g., concealed object 1094) under a covering 1093. In this case, the obtained terahertz image is image 1091. Image 1091 is an image in which an image from the covering 1093, an image from the concealed object 1094, and an image from the person's skin surface are superimposed. When focusing on the concealed object 1094, since an image other than the concealed object 1094 is superimposed on the image of the concealed object 1094, it may be difficult to identify the concealed object 1094.

Fig. 10(b) is a schematic diagram illustrating the superposition of multiple terahertz wave reflection images to explain this embodiment. Fig. 10(b) shows a schematic diagram of the subject 1092 shown in Fig. 10(a) and the main parts of the terahertz wave camera system 100 shown in Fig. 1. Below, an example of the case where reflection images are superimposed is explained using Fig. 10(b).

As shown in FIG. 10(a), the subject 1092 has a concealed object 1094 and a covering object 1093. In the X direction, the covering object 1093 is located between the concealed object 1094 and the transmitting unit 101a and the transmitting unit 101b. In FIG. 10(b), the directional axis of the terahertz wave is shown. The directional axis of the terahertz wave will be described later.

The transmitter 101a emits terahertz waves 117a, and the transmitter 101b emits terahertz waves 117b. Most of the terahertz waves 117a pass through the covering 1093 and are reflected by the surface 1094a of the concealed object 1094. The terahertz waves 117a become reflected terahertz waves 118a, and are detected by the receiver 102a. Most of the terahertz waves 117b are reflected by the surface 1093a of the covering 1093. The terahertz waves 117b become reflected terahertz waves 118b, and are detected by the receiver 102a. Here, the terahertz waves 117a and 117b are not limited to being entirely reflected or transmitted, and may be partially reflected or transmitted. Also, some of the terahertz waves 117a and 117b may be attenuated or absorbed. The terahertz wave detected by the receiver 102a is the sum of the reflected terahertz wave 118a and the reflected terahertz wave 118b, and contains information on the covering 1093 and the concealed object 1094. Therefore, an image 1091 as shown in FIG. 10(a) is acquired. Note that a portion of the terahertz wave 117a is reflected by the surface 1093a of the covering 1093 and becomes the reflected terahertz wave 119a, but since it does not enter the receiver 102a, a description thereof will be omitted.

Here, when acquiring an image of the concealed object 1094, it is desirable to detect only the reflected terahertz waves 118a. In other words, the image 1091 contains information that becomes noise, such as the covering 1093, and is unclear. Therefore, in the terahertz wave camera system 100 of this embodiment shown in FIG. 1, the control unit 103 performs the following control. This is a control to make the output of the transmitting unit 101b smaller than the output of the transmitting unit 101a, or to stop the transmitting unit 101b. By such control, it is possible to reduce the reflected terahertz waves 108b that become noise.

The terahertz wave camera system 100 of this embodiment has the following configuration. The configuration has multiple transmitters arranged at different positions, one receiver, and a control unit. The configuration has one transmitter, multiple receivers arranged at different positions, and a control unit. Alternatively, the configuration has multiple transmitters arranged at different positions, multiple receivers arranged at different positions, and a control unit. Such a configuration of the terahertz wave camera system 100 can reduce the reflected terahertz waves 108b that become noise. Therefore, the camera system 100 can obtain an image with reduced noise, with reduced superimposed images.

Figure 10 (c) shows the beam pattern (radiation pattern) of the terahertz waves emitted from each of the four transmitters 101a to 101d shown in Figure 1. As shown in Figure 1, transmitter 101a emits terahertz wave 107a, transmitter 101b emits terahertz wave 107b. Transmitter 101c emits terahertz wave 107c, and transmitter 101d emits terahertz wave 107d. Here, the directional axes of each of terahertz waves 107a to 107d are shown as terahertz waves 117a to 117d. As described above, terahertz waves 117a and 117b shown in Figure 10 (b) show the directional axes. The directional axis is the central axis of the directional characteristics of the terahertz waves from the transmitter. For example, it is a straight line indicating the direction in which the terahertz waves with the highest intensity are emitted from the transmitter. The directional axis can be obtained, for example, as follows. A number of concentric spheres of different radii are created, centered on the center of gravity of the transmitter. Then, the directional axis can be obtained by selecting the position on each sphere where the intensity of the terahertz wave is high and connecting these points. The directional axis can also be obtained by simulation. The terahertz wave in FIG. 10(b) is shown with a directional axis, but the terahertz wave in FIG. 10(b) is an electromagnetic wave with a spread as shown in FIG. 10(c).

The operation of the control unit 103 in this embodiment will be described in detail using FIG. 1. The control unit 103 controls the operation of the lighting unit 101. Each of the transmission units 101a to 101d of the lighting unit 101 can change its output and operation in response to a control signal from the control unit 103. Next, the control by the control unit 103 will be described in detail. In the following explanation, for ease of understanding, the control unit 103 will be described as controlling two transmission units 101a and 101b. However, the number of transmission units that the control unit 103 can control is not limited to this.

The control unit 103 can perform at least the following three controls. The control unit 103 can perform control to operate the transmitting unit 101a and stop the transmitting unit 101b. The control unit 103 sets the transmitting unit 101a in a state in which it irradiates the terahertz wave 107a, and sets the transmitting unit 101b in a state in which it does not irradiate the terahertz wave 107b. It can also be said that the control unit 103 can perform control to set the transmitting unit 101a in an irradiating state and the transmitting unit 101b in a non-irradiating state. In addition, the control unit 103 can perform control to stop the transmitting unit 101a and operate the transmitting unit 101b. The control unit 103 sets the transmitting unit 101a in a state in which it does not irradiate the terahertz wave 107a, and sets the transmitting unit 101b in a state in which it irradiates the terahertz wave 107b. It can also be said that the control unit 103 can perform control to set the transmitting unit 101a in a non-irradiating state and the transmitting unit 101b in an irradiating state. In other words, the control unit 103 can control switching between the presence and absence of output from the illumination unit 101. Hereinafter, the operating state is also referred to as "on" and the stopped state is also referred to as "off."

Here, the operating or irradiating state refers to a state in which terahertz waves are radiated, and the stopped or non-irradiating state refers to a state in which terahertz waves are not radiated. When the transmitter 101b is in a non-irradiating state, for example, the supply of power supply voltage to the transmitter 101b may be stopped. Also, when the transmitter 101b is in a non-irradiating state, a switch that controls whether or not the transmitter 101b radiates terahertz waves may be turned off. Also, when the transmitter 101b is in a non-irradiating state, a shield that blocks terahertz waves, for example a shutter, may be provided in the directional axis direction of the transmitter 101b.

Furthermore, the control unit 103 can control the adjustment of the output of the illumination unit 101. The illumination unit 101 includes a transmitting element that transmits terahertz waves, which will be described later, and the output of the illumination unit 101 can be adjusted by changing the operating point of the voltage or current of this transmitting element. Alternatively, if the illumination unit 101 includes multiple transmitting elements, the output of the illumination unit 101 can be adjusted by controlling the number of transmitting elements that are in operation. The change in output can be confirmed by using a detection device capable of detecting terahertz waves, or by using the detection unit 102 of the camera system 100. It can also be confirmed by a method of monitoring the operating point of the illumination unit 101.

For example, the control unit 103 can perform control to strengthen the output of the transmitting unit 101a relative to the output of the transmitting unit 101b. The control unit 103 can perform control to weaken the output of the transmitting unit 101a relative to the output of the transmitting unit 101b. The control unit 103 can perform control to make the output of the transmitting unit 101a and the output of the transmitting unit 101b equal.

The control unit 103 can also perform control to reduce the difference between the output of the transmitting unit 101a and the output of the transmitting unit 101b. The control unit 103 can perform control to increase the difference between the output of the transmitting unit 101a and the output of the transmitting unit 101b. The control unit 103 can perform control to change the output of the transmitting unit 101a and the output of the transmitting unit 101b while keeping the difference between the output of the transmitting unit 101a and the output of the transmitting unit 101b constant.

As described above, the number of transmitters that can be controlled by the control unit 103 is not limited to the above description. In other words, the control unit 103 can operate a specific transmitter among the multiple transmitters, stop a specific transmitter, or switch the output of a specific transmitter. The control unit 103 can also operate a transmitter that belongs to a specific group among the multiple transmitters, stop a transmitter that belongs to a specific group, or switch the output of a transmitter that belongs to a specific group. In this way, by the control unit 103 controlling the operation of the illumination unit 101, unwanted reflected terahertz waves can be reduced, making it possible to obtain an image with reduced noise.

The control unit 103 controls the illumination unit 101 in this manner based on information output from the image processing unit 105. Next, the operation of the image processing unit 105 will be described.

The image processing unit 105 generates a terahertz image based on the image data output from the detection unit 102. The image processing unit 105 then determines the shape and type of the subject 106 from the terahertz image. As shown in FIG. 1, the terahertz wave camera system may have a visible camera 109, and the image processing unit 105 may determine the shape of the subject 106 by comparing the terahertz image with a visible image from the visible camera 109. The visible image 944 includes shape information. The control unit 103 controls the illumination unit 101 by referring to the determination result. The configuration of the image processing unit 105 will be described with reference to FIG. 9.

9A is a diagram for explaining an example of the configuration of the image processing unit 105. The image processing unit 105 of this embodiment has an image generation unit 942 and a determination unit 945. The image generation unit 942 converts the image data 941 output by the detection unit 102 into a terahertz image 943. The image data 941 is unprocessed image data. The unprocessed image data is data output by the image sensor of the detection unit 102 as is, and is also called RAW data. The terahertz image 943 is data obtained by converting the image data 941 into a recording format suitable for post-processing. The determination unit 945 determines the object observed by the detection unit 102 with reference to the terahertz image 943. In this embodiment, the terahertz image 943 that has been subjected to post-processing is used at the time of determination. Note that it is also possible to perform the determination using image data at the time of determination. Hereinafter, including the case where a terahertz image is used, it may also be referred to as performing the determination based on image data.

In the judgment, for example, the total or partial match or correlation between the visible image 944 of the covering object 106b (see FIG. 1) from the visible camera 109 and the terahertz image 943 is calculated. Then, the judgment unit 945 judges which of the concealed object 106a and the covering object 106b has more information and which is being observed. Then, the image processing unit 105 passes the judgment result 946 to the control unit 103. The control unit 103 checks whether the designation of the object to be observed matches the judgment result 946, and if they do not match, controls the illumination unit 101.

Figure 9(b) is a diagram illustrating another example of the configuration of the image processing unit 105. The image processing unit 105 has an image generation unit 942, a determination unit 945, and a database 947. That is, the image processing unit 105 in Figure 9(b) has a database 947 in addition to the configuration of the image processing unit 105 in Figure 9(a). In the configuration in Figure 9(b), the visible camera 109 can be omitted.

The database 947 is stored, for example, in a memory space in the device, a server on a network, a storage medium, etc. The database 947 stores model image information including shape data of the subject 105. In detail, the terahertz image of the subject 105 acquired in advance and its conditions are stored. In addition, information obtained by processing the terahertz image (edge-enhanced image, etc.) is stored. In the configuration of FIG. 9B, the determination unit 945 makes a determination using the terahertz image held by the database 947 and the terahertz image 943 acquired by the detection unit 102. Since the visible image is an external image of the subject 106, the visible image 944 mainly has information on the covering object 106b. Therefore, when the visible image 944 and the terahertz image 943 are used for the determination, it is possible to determine whether the image shown by the terahertz image 943 is the covering object 106b. When the terahertz image of the database 947 and the terahertz image 943 are used for the determination, it is possible to determine whether the image shown by the terahertz image 943 is the concealed object 106a. The database 947 may have visible images, in which case it is easy to omit the visible camera. The information stored in the database 947 is not limited to shape information. For example, a classification filter based on statistical processing used for judgment created in advance, a trained machine learning model used for judgment, and a data set used for machine learning may be stored. In this embodiment, the information stored in these databases is also referred to as shape data.

Figure 9(c) is a diagram illustrating another example of the configuration of the image processing unit 105. The image processing unit 105 in Figure 9(c) has AI (Artificial Intelligence). The image processing unit 105 has an image generation unit 942, a database 947, and an AI unit 948. In detail, the AI unit 948 of the image processing unit 105 in Figure 9(c) replaces the determination unit 945 of the image processing unit 105 in Figure 9(b).

The AI unit 948 has a trained machine learning model. The trained machine learning model is constructed, for example, based on a data set related to image information including shape information in the database 947. Using the trained machine learning model, the image processing unit 105 can determine whether the terahertz image 943 is a concealed object 106a or a covering object 106b. The AI unit 948 may also have a deep learning function. Conventionally, a machine learning model requires supervised data in which an operator indicates a feature to be focused on. However, by providing the AI unit 948 with a deep learning function, the features can be automatically extracted. By providing the AI unit 948 with a deep learning function, the accuracy of the determination by the image processing unit 105 improves as the number of data sets increases.

In particular, it is preferable to use a deep learning function for learning the terahertz image 943. The visible image 944 is an image of scattered light from the subject 106 detected by the visible camera 109. On the other hand, the terahertz image 943 is an image of specularly reflected light from the subject 106 detected by the detection unit 102. Since the terahertz image 943 is an image of only the reflected terahertz waves that reach the detection unit 102, only a fragmentary shape of the subject 106 is imaged. In addition, the optical path of the specularly reflected light until it reaches the detection unit 102 changes depending on the posture of the subject 106. Therefore, the image of the fragmentary shape changes depending on the posture of the subject 106. In order to estimate and determine the subject 106 from fragmentary information, a determination using a deep learning function is useful.

Next, the operation of the terahertz wave camera system 100 of this embodiment will be described. First, a simple explanation of the operation and conditions will be given to facilitate understanding. FIG. 12(a) is a flow diagram for explaining the operation of the terahertz wave camera system 100 of this embodiment. FIG. 12(b) is a table for explaining the conditions. The conditions stipulate the control of the illumination unit 101 and the detection unit 102, and include a control sequence.

First, in step S1201, the shooting conditions are set. The shooting conditions are the control sequences of the illumination unit 101 and the detection unit 102. Here, the shooting conditions include at least the conditions 1231, 1232, and 1233 shown in FIG. 12(b). The condition 1231 operates the transmitting unit 101a and stops the transmitting unit 101b. The condition 1232 stops the transmitting unit 101a and operates the transmitting unit 101b. The condition 1233 increases the output of the transmitting unit 101a and decreases the output of the transmitting unit 101b. The condition may be to operate the transmitting unit 101a, stop the transmitting unit 101a, and operate the transmitting unit 101b, etc. The other conditions may be set in advance, but the amount of change, etc., may also be set by the image processing unit 105 as appropriate. Here, it is assumed that the condition 1231 is selected in step S1201 and the shooting conditions are set.

Next, imaging is performed under imaging conditions based on the condition 1231, and in step S1202, image data is acquired. A terahertz image is generated based on the image data. In step S1203, a desired determination is made, such as whether the information contained in the terahertz image is mainly information based on the covering 106b, or whether there is a matching concealed object 106a. Here, it is determined whether there is a concealed object 106a with which the terahertz image matches. In this determination, the shape data 1210 is used. If there is no concealed object 106a with which the terahertz image matches the shape data 1210 as determined in step S1203, the process returns to step S1201. Then, another condition, for example, the condition 1232, is selected as the imaging condition, and image data is acquired again. If it is determined in step S1203 that the terahertz image mainly contains information of the concealed object 106a that matches the shape data 1210, imaging is terminated. Since it is possible to identify imaging conditions under which noise is reduced, it is possible to acquire an image with reduced noise.

Next, another operation of the terahertz wave camera system 100 will be described. FIG. 13 is a flow diagram for explaining another operation of the terahertz wave camera system 100 of this embodiment. In FIG. 13, the flow has periods 1311, 1312, and 1313. Period 1311 is a preparation period for identifying the shooting conditions. Period 1312 is a judgment period. Periods 1311 and 1312 can also be set, for example, when the terahertz wave camera system 100 is installed, when the power is turned on, when the shooting mode is switched, etc. Steps S1301 to 1303 are similar to steps S1201 to S1203 shown in FIG. 12(a), so the description will be omitted. Condition 1331 can be selected from any condition as shown in FIG. 12(b).

Next, in the determination in step S1303, if the terahertz image mainly contains information about the concealed object 106a that matches the shape data 1332, step S1304 is performed. In step S1304, the shooting conditions of the terahertz image used in the determination are recorded. The record can be retained as condition 1333. Condition 1333 can also be called the actual shooting condition.

Next, in period 1313, the shooting conditions are set in step S1305. Condition 1333 is selected as the shooting conditions. Note that if there is no change to the shooting conditions, no change is made. Then, in step S1306, image data is acquired. Through this flow, it is possible to acquire image data with reduced noise.

To install the terahertz wave camera system 100, periods 1311 and 1312 may be performed, and then period 1313 may be performed during normal operation, or periods 1311 to 1313 may be repeated during normal operation.

Next, FIG. 5 is a flow diagram explaining the detailed operation of the terahertz wave camera system 100 of this embodiment. Here, an example of the operation for observing the concealed object 106a is explained. The flow of FIG. 5 corresponds to the flow of FIG. 13.

In the operational flow of this example, there are at least periods 531, 532, and 533. That is, the operation includes step S501, which corresponds to period 531, step S504, which corresponds to period 532, and step S509, which corresponds to period 533. Each time steps S501, S504, and S509 are performed, the operation of the device is switched.

The operation mode of the terahertz wave camera system 100 during period 531 is the imaging condition adjustment mode. During period 531, the control unit 103 sets the imaging conditions of the illumination unit 101 and the detection unit 102 to predetermined conditions in accordance with the device control sequence described below.

The operating mode of the terahertz wave camera system 100 during period 532 is a subject judgment processing mode. During period 532, the image processing unit 105 makes a judgment based on the image of the subject 106 captured under the shooting conditions set during period 531. Also, during period 532, the image processing unit 105 determines the shooting conditions (also referred to as the main shooting conditions) under which the terahertz wave camera system 100 will perform the main shooting based on the judgment result.

The operating mode of the terahertz wave camera system 100 in period 533 is the actual shooting mode. In period 533, the control unit 103 controls to perform actual shooting of the subject 106 under the shooting conditions determined by periods 531 and 532. For example, at least steps S501 to S502 may be performed during the standby period of the terahertz wave camera system 100, and at least step S509 may be performed during the shooting period of the terahertz wave camera system 100. In other words, the standby period of the terahertz wave camera system 100 may be overlapped with periods 531 and 532, and the shooting period of the terahertz wave camera system 100 may be overlapped with period 533.

The detailed flow will be described below. When the operation of the terahertz wave camera system 100 starts, the process moves to period 531 (step S501). In period 531, the control unit 103 controls each component of the terahertz wave camera system 100 based on the control sequence of condition 534. The control unit 103 controls the illumination unit 101 (step S502). The control unit 103 controls the terahertz wave 107a emitted by the transmitting unit 101a and the second terahertz wave 107b emitted by the transmitting unit 101b. Here, an example is described in which the control unit 103 controls the transmitting units 101a and 101b to control the terahertz waves emitted by them, but the control target of the control unit 103 is not limited to this. The control unit 103 may control only one transmitting unit 101a. For example, the control unit 103 of this embodiment may further control the transmitting units 101c and 101d to control the terahertz waves emitted by them. The control sequence of condition 534 stores multiple imaging conditions and the order in which the imaging conditions are performed. The control unit 103 in FIG. 1 controls the terahertz waves emitted from the illumination unit 101 based on the imaging conditions of the control sequence. For example, the control sequence of condition 534 stores the combination, power, and order of the terahertz waves emitted from each of the emission units 101a to 101d.

During period 531, the detection unit 102 measures the terahertz waves (step S503). The terahertz wave camera system 100 acquires image data 535 output from the detection unit 102. The image data 535 is converted by the image processing unit 105 into the terahertz image 943 described in FIG. 9.

After the image data 535 is acquired, the process proceeds to period 532 (step S504). In period 532, the imaging conditions (main imaging conditions) to be applied in period 533 to be subsequently transferred are determined based on the acquired image data 535. The imaging conditions used in this main imaging are called conditions 537. In condition 537, control information related to terahertz wave 107a of transmitter 101a used in period 533 and control information related to terahertz wave 107b of transmitter 101b are recorded. Furthermore, in this embodiment, control information related to the terahertz waves emitted by transmitters 101c and 101d is also recorded in condition 537. The imaging conditions used in the main imaging recorded in condition 537 in this embodiment include the selection of the operation of the irradiation state and non-irradiation state of the terahertz waves generated from each transmitter 101a, 101b, 101c, and 101d. Condition 537 is determined by image processing unit 105 based on the judgment of image processing unit 105 described below. The detailed operation flow of period 532 is described below.

In the image processing unit 105, similarity and correlation are extracted (step S505). In detail, at least one of the similarity and correlation between the terahertz image 943 obtained from the image data 535 and the shape data 536 is extracted. For example, the shape data 536 is the visible image 944 from the visible camera 109 described above. For example, the shape data 536 is information stored in the database 947 described above. In this embodiment, the similarity and correlation between the subject 106 and the covering 106b is extracted.

Next, the extracted result is used to determine whether or not it is the concealed object 106a (step S506). In detail, whether or not the terahertz image 943 is the concealed object 106a is determined. For example, in this embodiment, if the information of the terahertz image 943 has low similarity or correlation with the covering object 106b included in the shape data 536, it is determined to be the concealed object 106a. If it is determined that the concealed object 106a exists, it is determined that the subject 106 has the concealed object 106a. If the information of the terahertz image 943 has high similarity or correlation with the covering object 106b included in the shape data 536, it is determined that the terahertz image 943 is the covering object 106b. This shooting condition may be stored as the shooting condition for the covering object 106b.

When the subject 106 is determined to be the concealed object 106a, the photographing conditions used in the control sequence of the condition 534 are recorded as the condition 537 (main photographing conditions) (step S507). When recording, the condition 534 can be added to or updated as the main photographing conditions. For example, if the photographing conditions used to determine the concealed object 106a are not included in the main photographing conditions of the condition 537, the condition 534 is added to the condition 537. If the desired photographing conditions have already been recorded in the main photographing conditions of the condition 537, nothing is done. If a photographing condition different from the desired photographing condition, for example, the photographing condition of the covering object 106b, is recorded in the main photographing conditions of the condition 537, the photographing condition is updated and corrected. Note that in this embodiment, the subject 106 is determined to be the concealed object 106a, but the covering object 106b may also be determined.

Check whether the control sequence of condition 534 has ended (step S508). If the control sequence has not ended, return to period 531. If the control sequence has ended, transition to the actual shooting mode of period 533 (step S509).

In period 533, the subject 106 is photographed under the photographing conditions determined in periods 531 and 532. The control unit 103 controls the terahertz waves 107a emitted by the transmitting unit 101a and the terahertz waves 107b emitted by the transmitting unit 101b based on the photographing conditions in condition 537 (step S510).

In this embodiment, the transmitters 101a, 101b, 101c, and 101d are controlled according to the condition 537. For example, only the terahertz waves that contribute to the observation of the hidden object 106a are irradiated. When the terahertz waves that contribute to the observation of the hidden object 106a are only the reflected terahertz waves 108a, the control unit 103 puts the transmitter 101a in an irradiating state. Then, the terahertz waves 107a are irradiated to the subject 106. In this state, the terahertz wave camera system acquires a terahertz image (step S511). By capturing images under such capturing conditions, the reflected terahertz waves related to the undesired covering object 106b can be reduced. Therefore, it becomes easy to acquire an image related to the hidden object 106a with reduced information related to the covering object 106b. Although not described in this embodiment, it becomes easy to identify the hidden object 106a when identifying the hidden object 106a later.

By following this flow, unwanted reflected terahertz waves can be reduced, allowing images with reduced noise to be obtained.

Figure 6 is a diagram for explaining an image of a terahertz image acquired by the terahertz wave camera system 100 of this embodiment. The vicinity of the chest of the subject 106 is set as the observation region 641. By irradiating only the terahertz waves that contribute to the observation of the concealed object 106a, a terahertz image 642 of the concealed object 106a can be acquired as shown in Figure 6 (a). Conversely, when the observation target of the subject 106 is set to the covering 106b, an image in which a terahertz image 643 of the covering is emphasized can be acquired as shown in Figure 6 (b) by stopping only the terahertz waves that contribute to the observation of the concealed object 106b. Note that in this embodiment, the irradiation state and the stopped state of the terahertz waves are taken as examples, but the various operation examples of the control unit 103 described above can be applied.

The configuration of this embodiment makes it possible to obtain a terahertz image that reduces information other than the target object of interest, compared to the conventional image 1091 in which the concealed object 106a and the covering object 106b are superimposed, making it easier to improve the ability to identify the target object of interest.

Fig. 2(a) is a diagram for explaining a configuration example of the transmitting unit 101a constituting the illumination unit 101. The transmitting unit 101a has a transmitting element 211a and a transmitting element 211b arranged at a position different from that of the transmitting element 211a. In this embodiment, the transmitting unit 101a further has a transmitting element 211c and a transmitting element 211d. The transmitting element 211a emits a terahertz wave 207a, the transmitting element 211b emits a terahertz wave 207b, the transmitting element 211c emits a terahertz wave 207c, and the transmitting element 211d emits a terahertz wave 207d. The plane from which the terahertz waves 207a, 207b, 207c, and 207d are emitted from the transmitting elements 211a, 211b, 211c, and 211d is assumed to be a plane P1. The number of transmitting elements that the transmitting unit 101a has is not limited to this.

The transmitter 101a has a housing 200. Each of the multiple transmitter elements 211a, 211b, 211c, and 211d is installed on a support substrate 201 of the housing 200. The transmitter 101a has a control circuit 202. The control circuit 202 is provided in the housing 200, and in this embodiment, is provided on one surface that constitutes the outer shape of the housing 200. The control circuit 202 is electrically connected to the control unit 103, and controls the operation of the multiple transmitter elements 211a, 211b, 211c, and 211d in response to a control signal from the control unit 103. It can also be said that the housing 200 has the multiple transmitter elements 211a, 211b, 211c, and 211d, and the control circuit 202.

Each of the transmitting elements 211a, 211b, 211c, and 211d is an array of unit cells including an element (transistor or diode) having gain in the terahertz wave region and an antenna as an external resonant circuit. For example, a resonant tunneling diode (RTD) can be used as the element having gain. For details of the configuration in this case, refer to JP 2014-200065 A.

The plurality of transmitting elements 211a, 211b, 211c, and 211d are arranged in a line or two-dimensional shape. The terahertz wave 107a in FIG. 1 is a collection of the terahertz waves 207a, 207b, 207c, and 207d in FIG. 2, and the shape of the terahertz wave 107a differs depending on the arrangement of the plurality of transmitting elements 211a, 211b, 211c, and 211d. For example, in FIG. 1, the shape of the terahertz wave 107a on a virtual plane parallel to the plane P1 and away from the plane P1 in the radial direction is an arbitrary one-dimensional or two-dimensional shape. Here, since the terahertz wave is difficult to scatter on the skin surface, it is effective for the purpose of capturing the shape of the subject to arrange the plurality of terahertz wave transmitting elements in a planar (two-dimensional) shape and irradiate the terahertz wave from various angles. Therefore, by appropriately setting the arrangement of each transmitting element, it is possible to generate a terahertz wave having a one-dimensional or two-dimensional beam shape. By arranging the transmitting elements in a plane, terahertz waves can be incident on the observation point of the subject at multiple angles of incidence. As a result, multiple terahertz waves with different emission angles are emitted from the observation point, making it easier to increase the probability that the light beam of the terahertz wave from the observation point reaches the camera lens. In other words, by arranging the transmitting elements in a plane, it is possible to emit pseudo scattered terahertz wave light from the observation point of the subject. Such illumination unit 101a allows terahertz waves to be irradiated from various angles onto the subject 106, which is effective for the purpose of capturing the shape of the subject 106 with a terahertz wave camera.

Figure 2 (b) is a diagram explaining an example of the configuration of the transmitting unit 101b. The transmitting unit 101b has transmitting element 311a and transmitting element 311b arranged at a position different from that of transmitting element 311a. In this embodiment, the transmitting unit 101b further has transmitting element 311c and transmitting element 311d. Transmitting element 311a emits terahertz wave 307a, transmitting element 311b emits terahertz wave 307b, transmitting element 311c emits terahertz wave 307c, and transmitting element 311d emits terahertz wave 307d. The surface from which terahertz waves 307a, 307b, 307c, and 307d are emitted from transmitting elements 311a, 311b, 311c, and 311d is assumed to be surface P2. The number of transmitting elements that the transmitting unit 101b has is not limited to this. The transmitter 101b has a housing 300. Each of the transmitter elements 311a, 311b, 311c, and 311d is installed on a support substrate 301 of the housing 300. The transmitter elements 311a, 311b, 311c, and 311d are connected to the control unit 103, and their operation is controlled. The detailed configuration and arrangement of the transmitter 101b are the same as those of the transmitter 101a described above, and therefore will not be described.

In this embodiment, the process for obtaining an image of the concealed object 106a of the subject 106 has been described, but the covering 106b can also be selected as the target object. In other words, in a subject having multiple interfaces, it is also possible to reduce images due to reflected terahertz waves that occur at interfaces other than any of the interfaces.

In this embodiment, a determination is made as to whether the shape of the subject can be detected, but a determination may also be made as to whether the subject contains more noise components than a specified value. An example of a noise component is an unwanted reflected terahertz wave. The noise components can be detected by prior measurement and a specified value can be set.

The terahertz wave camera system of this embodiment makes it possible to obtain terahertz images with reduced noise.

Second Embodiment
The terahertz wave camera system of this embodiment will be described with reference to Fig. 3. The terahertz wave camera system of this embodiment is different from the camera system 100 of the first embodiment in the controlled object of the control unit 103. In the description of this embodiment, the description of the parts common to the first embodiment will be omitted.

Fig. 3(a) is a diagram for explaining a configuration example of the transmitting unit 101a constituting the illumination unit 101 of this embodiment. As with the transmitting unit 101a of the first embodiment shown in Fig. 2(a), it has a plurality of transmitting elements 211a, 211b, 211c, and 211d. The transmitting element 211a emits terahertz waves 207a, the transmitting element 211b emits terahertz waves 207b, the transmitting element 211c emits terahertz waves 207c, and the transmitting element 211d emits terahertz waves 207d. The plane from which the terahertz waves 207a, 207b, 207c, and 207d are emitted from the transmitting elements 211a, 211b, 211c, and 211d is assumed to be plane P1. The number of transmitting elements that the transmitting unit 101a has is not limited to this.

The transmitter 101a has a housing 200. Each of the multiple transmitter elements 211a, 211b, 211c, and 211d is installed on a support substrate 201 of the housing 200. Unlike the transmitter 101a of FIG. 2(a), the transmitter 101a of FIG. 3(a) does not have the control circuit 202 shown in FIG. 2(a). The control unit 103 is electrically connected to the multiple transmitter elements 211a, 211b, 211c, and 211d, and controls the operation of the multiple transmitter elements 211a, 211b, 211c, and 211d. The operation and detailed configuration of the other parts of the transmitter 101a are the same as those of FIG. 2(a), so a description thereof will be omitted.

Figure 3 (b) is a diagram for explaining an example of the configuration of the transmitting unit 101b constituting the illumination unit 101 of this embodiment. As with the transmitting unit 101b of the first embodiment shown in Figure 2 (b), it has a plurality of transmitting elements 311a, 311b, 311c, and 311d. Transmitting element 311a emits terahertz waves 307a, transmitting element 311b emits terahertz waves 307b, transmitting element 311c emits terahertz waves 307c, and transmitting element 311d emits terahertz waves 307d. The surface from which terahertz waves 307a, 307b, 307c, and 307d are emitted from transmitting elements 311a, 311b, 311c, and 311d is assumed to be surface P2. The number of transmitting elements that transmitting unit 101b has is not limited to this.

The transmitter 101b has a housing 300. Each of the multiple transmitter elements 311a, 311b, 311c, and 311d is installed on a support substrate 301 of the housing 300. Unlike the transmitter 101b of FIG. 2(b), the transmitter 101b of FIG. 3(b) does not have the control circuit 202 shown in FIG. 2(b). The control unit 103 is electrically connected to the multiple transmitter elements 311a, 311b, 311c, and 311d, and controls the operation of the multiple transmitter elements 311a, 311b, 311c, and 311d. The operation and detailed configuration of the other parts of the transmitter 101b are similar to those of the transmitter 101a, so a description thereof will be omitted.

In the first embodiment, the control unit 103 controls the transmitting units 101a, 101b, 101c, and 101d that constitute the illumination unit 101 (see FIG. 1). On the other hand, in this embodiment, the control unit 103 can also control the multiple transmitting elements that constitute the transmitting units 101a, 101b, 101c, and 101d. According to the configuration of this embodiment, the terahertz waves that contribute to the observation of the desired object can be controlled with finer precision, so that the SNR (signal-noise ratio) of the terahertz image is increased, making it easier to improve the ability to identify the object being observed. In addition, the configuration of the transmitting unit 101 can be simplified.

Third Embodiment
A terahertz wave camera system 400 of this embodiment will be described with reference to Fig. 4. This embodiment is different from the camera system 100 of the first embodiment in the configuration of the detection unit 102 and the configuration of the control unit. In the description of this embodiment, the description of the parts common to the first embodiment will be omitted.

Figure 4 is a diagram illustrating the configuration of a terahertz wave camera system 400 of this embodiment. The terahertz wave camera system 400 has at least an illumination unit 101, a detection unit 102, a control unit 103, a control unit 424, and an image processing unit 105. The illumination unit 101 irradiates a subject 106 with terahertz waves, and the detection unit 102 detects the terahertz waves reflected by the subject 106. The configuration of the subject 106 is the same as in the first embodiment, so a description thereof will be omitted. The terahertz wave camera system 400 has a visible camera 109. In addition to the configuration of the camera system 100 of the first embodiment, the terahertz wave camera system 400 further has a control unit 424.

The terahertz wave camera system 400 of this embodiment differs from the camera system 100 of the first embodiment in the configuration of the detection unit 102. The detection unit 102 has at least a receiving unit 102a and a receiving unit 102b arranged at a position different from that of the receiving unit 102a. The receiving unit 102a detects terahertz waves, and the receiving unit 102b receives and detects terahertz waves. FIG. 4 shows an example in which the detection unit 102 has receiving units 102c and 102d in addition to receiving units 102a and 102b. The number of receiving units that the detection unit 102 has is not limited to this.

The control unit 103 controls the operation of the illumination unit 101 as in the first embodiment. The control unit 424 controls the operation of the detection unit 102. In this embodiment, the control units 103 and 424 communicate with each other and control the operation of the illumination unit 101 and the detection unit 102, but the image processing unit 105 may be an overall control unit that controls the entire camera system. The control unit 424 controls the operation of the receiving units 102a to 102d, and controls the output of image data based on the received terahertz waves.

The image processing unit 105 may, for example, generate a terahertz image from image data output by the receiving unit 102a, and may also generate a terahertz image from image data output by the receiving unit 102b. The image processing unit 105 may, for example, combine two sets of image data output by the two receiving units 102a and 102b to generate one terahertz image. The detailed configuration of the image processing unit 105 is the same as that of the first embodiment, and the terahertz image can be generated by the image generating unit 942 in FIG. 9(a) or the like.

Here, the terahertz wave camera system 400 of this embodiment will be described with reference to FIG. 10(a) and FIG. 11. FIG. 10(a) is an image diagram for explaining the superposition of multiple terahertz wave reflection images for explaining this embodiment. FIG. 11 is a schematic diagram for explaining the superposition of multiple terahertz wave reflection images for explaining this embodiment. FIG. 11 shows a schematic view of the subject 1092 shown in FIG. 10(a) and the main parts of the terahertz wave camera system 400 shown in FIG. 4. Hereinafter, an example of the case where the reflection images are superimposed will be described with reference to FIG. 11. Note that FIG. 11 corresponds to FIG. 10(b) described in the first embodiment, and therefore the same components as those shown in FIG. 10(b) are assigned the same reference numerals and will not be described.

The subject 1092 has a concealed object 1094 and a covering object 1093 as shown in FIG. 10(a). In the X direction, the covering object 1093 is located between the concealed object 1094 and the receiving unit 102a and the receiving unit 102b. In FIG. 10(c), the directional axis of the terahertz wave is shown. The directional axis is as described in the first embodiment.

The transmitter 101a emits terahertz waves 117a. A part of the terahertz waves 117a is reflected by the surface 1093a of the covering 1093, and another part of the terahertz waves 117a is reflected by the surface 1094a of the concealed object 1094. A part of the terahertz waves 117a becomes reflected terahertz waves 118a and is detected by the receiver 102a. Another part of the terahertz waves 117a becomes reflected terahertz waves 118b and is detected by the receiver 102b. Note that a part of the terahertz waves 117a may be attenuated or absorbed. The reflected terahertz waves 118a detected by the receiver 102a have information about the concealed object 1094, and the reflected terahertz waves 118b detected by the receiver 102b have information about the covering. When an image is generated based on the reflected terahertz waves 118a and 118b detected by the two receiving units 102a and 102b, an image 1019 is generated in which the covering object 1093 and the concealed object 1094 are superimposed, as shown in FIG. 10(a).

Here, when acquiring an image of the concealed object 1094, it is desirable to detect only the reflected terahertz waves 118a. In other words, the image 1091 contains information that becomes noise, such as the covering 1093, and is unclear. Therefore, in the terahertz wave camera system 400 of this embodiment shown in FIG. 4, the control unit 424 performs the following control. This is a control to make the output of the receiving unit 102a greater than the output of the receiving unit 102b, or to stop the receiving unit 102b. By performing such control, it is possible to reduce the reflected terahertz waves 108b that become noise. As a result, the terahertz wave camera system 400 can obtain an image with reduced superimposed images and reduced noise.

Furthermore, in the terahertz wave camera system 400 of this embodiment shown in FIG. 4, as described in the first embodiment, the control unit 103 can control the operation of the illumination unit 101. Therefore, by controlling both the illumination unit 101 and the detection unit 102, it is possible to obtain a terahertz image with reduced noise.

The control by the control unit 424 will be described in detail. In the following description, for ease of understanding, the control unit 424 will be described as controlling two receiving units 102a and 102b. However, the number of receiving units that the control unit 424 can control is not limited to this.

The control unit 424 can perform at least the following three types of control. The control unit 424 can perform control to start the output of image data from the receiving unit 102a and stop the output of image data from the receiving unit 102b. The control unit 424 can perform control to stop the output of image data from the receiving unit 102a and start the output of image data from the receiving unit 102b. The control unit 424 can perform control to start the output of image data from the receiving unit 102a and the output of image data from the receiving unit 102b. In other words, the control unit 424 can perform control to switch between the presence and absence of output from the detection unit 102.

Furthermore, the control unit 424 can perform control to adjust the output of the detection unit 102. For example, the control unit 424 can perform control to increase the signal gain of the image data of the receiving unit 102a relative to the signal gain of the image data of the receiving unit 102b. The control unit 424 can perform control to decrease the signal gain of the image data of the receiving unit 102a relative to the signal gain of the image data of the receiving unit 102b. The control unit 424 can perform control to equalize the signal gain of the image data of the receiving unit 102a and the signal gain of the image data of the receiving unit 102b.

The control unit 424 can also perform control to reduce the difference between the signal gain of the image data of the receiving unit 102a and the signal gain of the image data of the receiving unit 102b. The control unit 424 can perform control to increase the difference between the signal gain of the image data of the receiving unit 102a and the signal gain of the image data of the receiving unit 102b. The control unit 424 can perform control to change the image data signal gain from the two receiving units 102a and 120b while keeping the difference between the signal gain of the image data of the receiving unit 102a and the signal gain of the image data of the receiving unit 102b constant. Changing the gain of the output of the receiving unit is performed, for example, by adjusting the amplification factor of the pixel circuit of the receiving unit or the amplifier circuit of the signal processing circuit of the receiving unit. Alternatively, the output of the receiving unit is adjusted by digitally adjusting the output of the receiving unit through signal processing. The method of adjusting the output of the receiving unit is not limited to these.

The control unit 424 can also reduce the resolution by stopping the operation of some of the multiple receiving elements in the receiving unit, thinning out the elements by stopping their output, or adding up the signals of multiple receiving elements.

As described above, the number of receiving units that the control unit 424 can control is not limited to the above description. In other words, the control unit 424 can operate a specific receiving unit among the multiple receiving units, stop a specific receiving unit, or switch the output of a specific receiving unit. Furthermore, the control unit 424 can operate a receiving unit that belongs to a specific group among the multiple receiving units, stop a receiving unit that belongs to a specific group, or switch the output of a receiving unit that belongs to a specific group. In this way, by the control unit 424 controlling the operation of the detection unit 102, it is possible to reduce undesired reflected terahertz waves, and therefore it is possible to obtain an image with reduced noise.

The control unit 424 controls the detection unit 102 in this manner based on information output from the image processing unit 105. Next, the operation of the image processing unit 105 will be described.

In the image processing unit 105, as in the first embodiment, a terahertz image based on the image information output from the detection unit 102 is generated, and the shape and type of the subject 106 are determined from the terahertz image. In this embodiment, as in the first embodiment, the terahertz wave camera system may have a visible camera 109. In that case, the image processing unit 105 can also determine the shape of the subject 106 by comparing the terahertz image with a visible image from the visible camera 109. The visible image 944 can also be called shape data. With reference to this determination result, the control unit 103 controls the operation of the illumination unit 101, and the control unit 424 controls the operation of the detection unit 102. The configuration of the image processing unit 105 is the same as in the first embodiment, so a description thereof will be omitted.

The operation of the terahertz wave camera system of this embodiment will be described. Figure 7 is a diagram illustrating the operation flow of the terahertz wave camera system 400 of this embodiment. Here, as in the first embodiment, the operation flow for observing the concealed object 106a will be described.

The operation of the terahertz wave camera system 400 includes at least periods 731, 732, and 733. That is, the operation includes step S701, which corresponds to period 731, step S704, which corresponds to period 732, and step S709, which corresponds to period 733. The operation of the device switches each time steps S701, S704, and S709 are performed.

The operation mode of the terahertz wave camera system 400 during period 731 is the imaging condition adjustment mode. During period 731, the control unit 103 and the control unit 424 set the imaging conditions of the illumination unit 101 and the detection unit 102 to predetermined conditions according to the device control sequence described below.

The operating mode of the terahertz wave camera system 400 during period 732 is a subject judgment processing mode. During period 732, the image processing unit 105 makes a judgment based on the image of the subject 106 captured under the shooting conditions set during period 731. Also, during period 732, the image processing unit 105 determines the shooting conditions (also referred to as the main shooting conditions) under which the terahertz wave camera system 400 will perform the main shooting based on the judgment result.

The operating mode of the terahertz wave camera system 400 during period 733 is the actual imaging mode. During period 733, the control unit 103 and the control unit 424 perform control so as to perform actual imaging of the subject 106 under the imaging conditions determined by periods 731 and 732. Periods 731 and 732 may be performed during the standby period of the terahertz wave camera system 400, and period 733 may be performed during the imaging period of the terahertz wave camera system 400.

The detailed flow will be described below. When the operation of the terahertz wave camera system 400 starts, the process moves to period 731 (step S701). In period 731, the control unit 103 and the control unit 424 control each component of the terahertz wave camera system 400 based on the control sequence of condition 734 (step S502). In this embodiment, the control unit 103 controls the operation of the illumination unit 101, and the control unit 424 controls the operation of the detection unit 102. Specifically, the control unit 103 controls the terahertz waves output by the transmission unit 101a and the terahertz waves output by the transmission unit 101b. The control unit 424 controls the output of image data from the reception unit 102a and the output of image data from the reception unit 102b. Here, an example is described in which the control unit 103 controls the transmission unit 101a and the transmission unit 101b to control the terahertz waves emitted by them, and the control unit 424 controls the reception unit 102a and the reception unit 102b to control the output of their image data. However, the objects controlled by the control unit 103 and the control unit 424 are not limited to these. The control unit 424 may control only one receiving unit 102a and control the output of image data from the receiving unit 102a. The control unit 424 may also control the receiving units 102c and 102d and control the output of image data from these units. The control unit 103 is the same as in the first embodiment, so a description thereof will be omitted. The control sequence of the condition 734 stores a plurality of shooting conditions and the order in which the shooting conditions are performed. The control unit 103 and the control unit 424 control the terahertz waves emitted from the illumination unit 101 and the output of image data from the detection unit 102 based on the shooting conditions of the control sequence. For example, the control sequence of the condition 734 stores the combination and order of the terahertz waves emitted from each of the transmitting units 101a to 101d and the combination and order of each of the receiving units 102a to 102d.

During period 731, the detection unit 102 measures the terahertz waves (step S703). The terahertz wave camera system 400 acquires image data 735 including either or both of the image data output from the receiving unit 102a and the receiving unit 102b. In the case of FIG. 4, image data including either, any combination, or all of the image data output from each of the receiving units 102a to 102d is output. The image data 735 is converted by the image processing unit 105 into the terahertz image 943 described in FIG. 9.

After the image data 735 is acquired, the process proceeds to period 732 (step S704). In period 732, the imaging conditions (main imaging conditions) to be applied in period 733 to be transitioned to later are determined based on the acquired image data 735. The imaging conditions used in the main imaging are called conditions 737. In conditions 737, control information related to the terahertz wave 107a of the transmitting unit 101a used in period 733, control information related to the terahertz wave 107b of the transmitting unit 101b, control information related to the image data of the receiving unit 402a, and control information related to the image data of the receiving unit 402b are recorded. In addition, control information related to other transmitting units and receiving units can also be recorded. Conditions 737 are determined in the image processing unit 105 based on the judgment of the image processing unit 105 described later. A detailed operation flow of period 732 is described below.

The image processing unit 105 extracts similarities and correlations (step S705). Next, the subject 106 is identified using the extracted results (step S706). If the subject 106 is identified as a concealed object 106a, the imaging conditions of the illumination unit 101 and the detection unit 102 used in the control sequence of condition 734 are recorded as condition 737 (main imaging conditions) (step S707). The end of the control sequence of condition 734 is confirmed (step S708). If the control sequence has not ended, the process returns to period 731. If the control sequence has ended, the process moves to the main imaging mode of period 733 (step S709). The processes of steps S705 to S709 are the same as steps S505 to S509 in the first embodiment, and therefore detailed explanations are omitted.

In period 733, the subject 106 is photographed under the photographing conditions determined in periods 531 and 532. The control unit 103 and the control unit 424 control the illumination unit 101 and the detection unit 102 based on condition 537 (step S710). The control unit 103 controls the operation of the transmission units 101a and 101b based on the photographing conditions of condition 537, and controls the terahertz waves 107a and 107b emitted by them. The control unit 424 controls the operation of the reception units 102a and 102b, and controls the output of image data. For example, only the terahertz waves contributing to the observation of the concealed object 106a are irradiated, and only the image data contributing to the observation of the concealed object 106a is output. Taking the models of Figures 10(b) and 11 as examples, the transmitter 101a that emits the terahertz wave 107a that becomes the reflected terahertz wave 108a that contributes to the observation of the concealed object 106a is set to an irradiating state. The receiver 102a that receives the reflected terahertz wave 108a that contributes to the observation of the concealed object 106a is controlled to output image data.

By controlling the control unit 103 and the control unit 424 as in step S710, the terahertz wave camera system 400 can acquire a terahertz image with reduced noise (step S711). By capturing an image under such capturing conditions, the reflected terahertz waves from the unwanted covering object 106b can be reduced. This makes it easy to acquire an image of the concealed object 106a with reduced information about the covering object 106b. Although not described in this embodiment, it also becomes easy to identify the concealed object 106a later when identifying the concealed object 106a.

In this embodiment, the control unit 103 and the control unit 424 do not have to be two physical entities. Furthermore, the control unit 103, the control unit 424, and the image processing unit 105 may be one physical entity.

Fourth Embodiment
A terahertz wave camera system 800 according to this embodiment will be described with reference to Fig. 8. In the description of this embodiment, descriptions of parts common to other embodiments will be omitted.

Figure 8 is a diagram illustrating the configuration of a terahertz wave camera system 800 of this embodiment. The terahertz wave camera system 800 has at least an illumination unit 101, a detection unit 102, a control unit 424, and an image processing unit 105. The terahertz wave camera system 400 further has a visible camera 109. The configuration of these components is similar to that of the other embodiments, so a description thereof will be omitted.

In the terahertz wave camera system 800 of this embodiment, the illumination unit 101 has only one transmitter 101a and does not have a control unit 103. The camera system 100 of the first embodiment controls the operation of the illumination unit 101, and the camera system 400 of the third embodiment controls the operation of both the illumination unit 101 and the detection unit 102. The camera system 800 of this embodiment controls the operation of the detection unit 102. The operation of the control unit 424 and the flow of the camera system of this embodiment are similar to the operation of the control unit 424 and the flow of the camera system of the third embodiment.

In this way, by appropriately adjusting the operation of at least one of the illumination unit 101 and the detection unit 102, noise in the terahertz image can be reduced.

Fifth Embodiment
FIG. 14 is a diagram for explaining the learning phase and the estimation phase of the AI unit that performs the judgment performed in the terahertz wave camera system. In this example, the case of judging a concealed object will be explained. FIG. 14(a) is a conceptual diagram of the learning phase. The learning model 1410 has an algorithm for shape judgment. Teacher data is input to the learning model 1410. For example, the teacher data is a concealed object image 1402. In addition, depending on the judgment, terahertz images such as a covering object image 1401, a covering object and a concealed object image 1403 can be used as teacher data. The covering object image 1401 includes a plurality of terahertz images each of which is a different covering object. In addition, the covering object image 1401 includes a plurality of terahertz images each of which is a covering object under the operation of the different illumination unit 101. The concealed object image 1402 includes a plurality of terahertz images each of which is a different concealed object. In addition, the covering object image 1401 includes a plurality of terahertz images each of which is a concealed object under the operation of the different illumination unit 101. The concealed object image 1402 includes an image (shape data) showing the contour of the concealed object. The covering object and concealed object image 1403 includes a plurality of terahertz images obtained by photographing different covering objects and concealed objects. The covering object and concealed object image 1403 includes a plurality of terahertz images obtained by photographing the covering object and concealed object under the operation of different illumination units 101. For example, the covering object image 1401, the concealed object image 1402, and the covering object and concealed object image 1403 may each have a visible light image. The images included in the covering object image 1401, the concealed object image 1402, and the covering object and concealed object image 1403 are each assigned a label. By inputting the teacher data, a trained model 1411 with higher accuracy is generated by the algorithm of the learning model 1410.

Specific algorithms for machine learning may include nearest neighbor methods, naive Bayes methods, decision trees, and support vector machines. Deep learning may also be used, in which a neural network is used to generate features and connection weighting coefficients for learning. For example, a CNN (Convolutional Neural Network Model) may be used as a deep learning model.

Fig. 14(b) is a conceptual diagram of the estimation phase. When a captured terahertz image 1420 is input to a trained model 1411 constructed in the learning phase, a result of identifying a concealed object is output. The terahertz image 1420 is, for example, an image based on the image data acquired in step S1202 in Fig. 12(a). The processing using this trained model 1411 can be executed, for example, by the image processing unit 105 in Fig. 1.

Sixth Embodiment
In this embodiment, another operation flow of the terahertz wave camera system 100 described in the first embodiment will be described with reference to Fig. 15. In the description of this embodiment, a description of parts common to the other embodiments will be omitted.

The terahertz wave camera system 100 of this embodiment has the configuration shown in FIG. 1. The visible camera 109 may or may not be included.

Depending on the surface shape of the subject, the change in the angle of the surface is complex and different for each subject. Therefore, the optimal positional relationship between the illumination unit, which is the light source, and the detection unit may change for each subject. Furthermore, when the subject moves, the positional relationship between the illumination unit, which is the light source, and the detection unit may change from moment to moment. Depending on such changes in positional relationship, there is a possibility that undesired reflected terahertz waves may be detected among the terahertz waves reflected by the subject. In such a case, the image will have components of the undesired reflected terahertz waves superimposed on it, resulting in a noisy image.

Figure 15 is a flow diagram explaining the operation flow of this embodiment. This embodiment is characterized by the method of operation of the illumination unit 101. The operation of the illumination unit 101 is controlled by the control unit 103. In the illumination unit 101, the transmitting units 101a to 101d are turned on in sequence, and images are captured by each of the transmitting units 101a to 101d. The flow in Figure 15 shows the operation during the capture period. In the initial state, the transmitting units 101a to 101d are off.

The oscillator 101a is turned on (step S1501), and the receiver 102 detects a signal based on the terahertz waves from the transmitter 101a (step S1502). Then, the transmitter 101a is turned off (step S1503). Steps S1501 and S1502 allow an image based on the terahertz waves from the transmitter 101a to be acquired. Next, the oscillator 101b is turned on (step S1504), and the receiver 102 detects a signal based on the terahertz waves from the transmitter 101b (step S1505), and the transmitter 101b is turned off (step S1506). Steps S1504 and S1505 allow an image based on the terahertz waves from the transmitter 101b to be acquired. Next, the oscillator 101c is turned on (step S1507), the receiver 102 detects a signal based on the terahertz waves from the transmitter 101c (step S1508), and the transmitter 101c is turned off (step S1509). Through steps S1507 and S1508, an image based on the terahertz waves from the transmitter 101c can be obtained. Then, the oscillator 101d is turned on (step S1510), the receiver 102 detects a signal based on the terahertz waves from the transmitter 101d (step S1511), and the transmitter 101d is turned off (step S1512). Through steps S1510 and S1511, an image based on the terahertz waves from the transmitter 101d can be obtained.

In this way, by sequentially turning on the multiple transmitters 101a to 101d, it becomes easy to select and acquire a suitable image that is not dependent on the surface shape of the subject. This is also particularly suitable when the subject moves.

These transmitting units 101a to 101d are controlled by the control unit 103. The control unit 103 can select from a number of operations. The number of operations includes at least an operation of turning on transmitting unit 101a and turning off transmitting units 101b to 101d, and an operation of turning on transmitting unit 101b and turning off transmitting units 101a, 101c, and 101d. The number of operations also includes at least an operation of turning on transmitting unit 101c and turning off transmitting units 101a, 101b, and 101d, and an operation of turning on transmitting unit 101d and turning off transmitting units 101a to 101c.

Also, while performing the operation flow shown in FIG. 15, suitable shooting conditions may be determined as shown in FIG. 5. That is, during period 531 in the operation flow of FIG. 5, the operation flow of FIG. 15 may be performed and shooting conditions may be extracted from at least four images. That is, after the operation flow of FIG. 15, a judgment may be performed and shooting conditions may be extracted. In addition to detecting the shape and type of the subject, the judgment may be performed by selecting an image whose noise component does not exceed a specified value, or by comparing noise components and selecting an image whose noise component is the smallest. Then, the subject may be photographed using the extracted shooting conditions. The shooting conditions may be extracted, for example, when the posture of the subject changes more than the standard. Also, the shooting conditions may be extracted periodically at a predetermined time interval and the shooting conditions may be updated.

In this embodiment, the transmitters 101a to 101d are turned on in sequence, but this is not limited to the above. For example, transmitters 101a and 101b are turned on simultaneously, the receiver 102 detects this, and transmitters 101a and 101b are turned off. After that, transmitters 101c and 101d are turned on simultaneously, the receiver 102 detects this, and transmitters 101c and 101d are turned off.

Transmitting units 101a to 101d are arranged along any one direction as shown in FIG. 1. This can be applied to multiple transmitting units arranged along one direction. It can also be applied to multiple transmitting units arranged across an aisle, not just in one direction.

The transmitters 101a to 101d are switched on in sequence along the direction of the arrangement, but the order does not have to be in the order of the direction of the arrangement and can be changed as appropriate.

The operation flow of this embodiment can also be modified as follows. The operations of turning off each of the transmitting units 101a to 101c shown in steps S1503, S1506, and S1509 may be performed simultaneously with the operations of turning on each of the transmitting units 101b to 101d shown in steps S1504, S1507, and S1510.

The terahertz wave camera system of the present invention is not limited to the configuration of the above-mentioned embodiment. For example, the terahertz wave camera system may not have a visible camera, and the control unit may be provided outside the system. For example, the control unit 103, the control unit 424, and the image processing unit 105 may be physically integrated and stored in a server provided on a network. In the above-mentioned embodiment, the focus is on the covering and the concealed object, but reflection on the skin surface of the human body can also be taken into consideration. In addition, the terahertz wave camera system of the present invention can be applied to any location, such as not only security gates, but also stairs, escalators, elevators, and walk-through passages. The configurations described in each embodiment can be combined as appropriate. According to the configuration of the present invention, it is possible to obtain a terahertz image with reduced noise.

REFERENCE SIGNS LIST 101 Illumination unit 102 Detection unit 103 Control unit 105 Image processing unit 106 Subject 109 Visible camera

Claims (13)

a first transmitter capable of emitting a first terahertz wave;
a second transmitter capable of emitting a second terahertz wave and disposed at a position different from that of the first transmitter;
a detection unit capable of detecting at least a first reflected terahertz wave that is a part of the first terahertz wave reflected from an object and a second reflected terahertz wave that is a part of the second terahertz wave reflected from the object, and outputting image data based on the detected terahertz waves;
A first control unit controls at least one of an operation of the first transmitting unit and an operation of the second transmitting unit under a condition set based on the image data,
the condition set based on the image data is an imaging condition when image data based on the first reflected terahertz wave and image data based on the second reflected terahertz wave are compared to obtain image data having less noise components,
The terahertz wave camera system is characterized in that, when the result of the comparison shows that the noise components of image data based on the first reflected terahertz wave are lower than the noise components of image data based on the second reflected terahertz wave, the first control unit operates the first transmitter and stops the second transmitter, or controls the output of the first terahertz wave from the first transmitter to be higher than the output of the second terahertz wave from the second transmitter . The terahertz wave camera system includes:
a first period in which operations of the first transmitting unit and the second transmitting unit are controlled based on a first condition that specifies control of the first transmitting unit and the second transmitting unit;
a second period in which a second condition for defining control of the first transmitting unit and the second transmitting unit is created based on the first image data output from the detecting unit during the first period;
2. The terahertz wave camera system according to claim 1, further comprising: a third period for controlling operation of the first transmitter and the second transmitter based on the second condition after the second period, and acquiring second image data output from the detector. the detection unit has a first receiving unit capable of detecting terahertz waves, and a second receiving unit that is arranged at a position different from the first receiving unit and is also capable of detecting terahertz waves,
The terahertz wave camera system according to claim 1 or 2 , further comprising a second control unit that controls at least one of the operation of the first receiving unit and the operation of the second receiving unit. The second control unit is
Controlling the first receiving unit to output image data and the second receiving unit to stop outputting image data;
4. The terahertz wave camera system according to claim 3, further comprising at least one of controls for stopping the output of image data from the first receiving unit and for causing the second receiving unit to output image data. 5. The terahertz wave camera system according to claim 3 , wherein control is performed to change a signal gain of the image data of the first receiving unit and a signal gain of the image data of the second receiving unit. The terahertz wave camera system includes:
a fourth period in which a third condition is set to define control of the first transmitting unit, the second transmitting unit, the first receiving unit, and the second receiving unit, and operations of the first transmitting unit, the second transmitting unit, the first receiving unit, and the second receiving unit are controlled based on the third condition;
a fifth period in which a fourth condition is created that defines control of the first transmitting unit, the second transmitting unit, the first receiving unit, and the second receiving unit based on image data output from at least one of the first receiving unit and the second receiving unit during the fourth period;
6. The terahertz wave camera system according to claim 3, further comprising: a sixth period, which is followed after the fifth period by controlling operation of the first transmitter, the second transmitter, the first receiver, and the second receiver based on the fourth condition, and acquiring image data output from at least one of the first receiver and the second receiver. 7. The terahertz wave camera system according to claim 1, further comprising an image processing unit that generates a terahertz image based on image data output from the detection unit and determines a shape of the subject from the terahertz image. The image processing unit has a database for storing model image information including shape data of the subject.
8. The terahertz wave camera system according to claim 7 . The terahertz wave camera system according to claim 7 , wherein the image processing unit has an AI unit. The terahertz wave camera system according to claim 9 , wherein the AI unit has a deep learning function. The AI unit has a trained machine learning model,
The terahertz wave camera system according to claim 9 , wherein the machine learning model is constructed based on image information including shape data. An image processing unit is included,
12. The terahertz wave camera system according to claim 1, wherein the image processing unit generates an image from the image data. 13. The terahertz wave camera system according to claim 1, further comprising a visible camera.

Images