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1. (US20170017852) DETECTING DEVICE, DETECTING METHOD, AND RECORDING MEDIUM
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TECHNICAL FIELD

      The present disclosure relates to a detecting device, detecting method, and non-transitory recording medium.

BACKGROUND ART

      Face authentication techniques for analyzing face images captured by a camera and authenticating the individual (simply termed face authentication hereafter) are known. A problem with such face authentication is unjust authentication in which someone else impersonates an individual by using a photograph of the individual. Moreover, various techniques for preventing unjust authentication due to impersonation are known.
      For example, Patent Literature 1 describes a technique of three-dimensional detection using multiple face images for preventing unjust authentication due to impersonation using photographs or the like.

CITATION LIST

Patent Literature

      Patent Literature 1: Unexamined Japanese Patent Application Kokai Publication No. 2012-069133.

SUMMARY OF INVENTION

Technical Problem

      However, if someone disguises himself as an individual by wearing a sophisticated disguising mask, the figure is three-dimensional and the above three-dimensional detection technique fails to prevent unjust authentication.
      Moreover, with recent sophisticated disguising masks, even the human eye sometimes fails to judge whether a disguising mask is worn. For example, at an airport immigration, a person wearing a disguising mask may clear visual matching by an immigration officer by using a forged passport with a photograph of the disguising mask.
      In addition to the above case of a disguising mask, similar disguise can be made by using something to disguise that is difficult to visually judge (for example, a sheet of something resembling skin in appearance). In view of such a circumstance, a technique for detecting things to disguise that are difficult to visually judge with high accuracy is demanded.
      The present disclosure is made with the view of the above situation and an objective of the disclosure is to provide a detecting device, detecting method, and non-transitory recording medium for detecting things to disguise with high accuracy.

Solution to Problem

      In order to achieve the above objective, the detecting device according to a first exemplary aspect of the present disclosure comprises:

an image acquirer acquiring images in multiple different wavelength ranges of reflected light of light emitted at a person; and

a determiner determining whether luminances of a face region in the images acquired by the image acquirer satisfy specific relations different from relations exhibited by skin.

an image acquirer acquiring images in multiple different wavelength ranges of reflected light of light emitted at a person; and

a determiner determining whether luminances of a face region in the images acquired by the image acquirer satisfy specific relations different from relations exhibited by skin.

      In order to achieve the above objective, the detecting method according to a second exemplary aspect of the present disclosure comprises:

an image acquisition step of acquiring images in multiple different wavelength ranges of reflected light of light emitted at a person; and

a determination step of determining whether luminances of a face region in the images acquired in the image acquisition step satisfy specific relations different from relations exhibited by skin.

an image acquisition step of acquiring images in multiple different wavelength ranges of reflected light of light emitted at a person; and

a determination step of determining whether luminances of a face region in the images acquired in the image acquisition step satisfy specific relations different from relations exhibited by skin.

      In order to achieve the above objective, the non-transitory recording medium according to a third exemplary aspect of the present disclosure saves a program that allows a computer to function as:

a determiner determining whether luminances of a face region in images of a person captured in multiple different wavelength ranges satisfy specific relations different from relations exhibited by skin.

a determiner determining whether luminances of a face region in images of a person captured in multiple different wavelength ranges satisfy specific relations different from relations exhibited by skin.

Advantageous Effects of Invention

      The present disclosure makes it possible to detect things resembling skin in appearance with high accuracy.

BRIEF DESCRIPTION OF DRAWINGS

       FIG. 1 is a graphical representation showing the spectra of luminances of reflected light when light is emitted at human skin and silicone;
       FIG. 2 is a block diagram showing the configuration of the disguising mask detecting device in embodiments;
       FIG. 3 is a diagram showing the structure of the camera in the embodiments;
       FIG. 4A is an illustration showing an exemplary visible light image;
       FIG. 4B is an illustration showing regions in the visible light image shown in FIG. 4A;
       FIG. 5 is a flowchart showing an exemplary process flow of the mask detection procedure;
       FIG. 6 is a flowchart showing an exemplary process flow of the mask determination procedure in Embodiment 1;
       FIG. 7 is a flowchart showing an exemplary process flow of the mask determination procedure in Embodiment 2;
       FIG. 8 is a flowchart showing an exemplary process flow of the mask determination procedure in Embodiment 3; and
       FIG. 9 is a block diagram showing another exemplary configuration of the disguising mask detecting device 1 shown in FIG. 2.

DESCRIPTION OF EMBODIMENTS

      Embodiments of the present disclosure will be described in detail hereafter with reference to the drawings.

Embodiment 1

      A disguising mask detecting device 1 according to Embodiment 1 of the present disclosure is installed, for example, near an entry gate in an airport immigration area. The disguising mask detecting device 1 has the function of determining whether a person who intends to pass through the entry gate wears a disguising mask and when he wears a disguising mask, giving notice accordingly.
      Here, the disguising mask detected by the disguising mask detecting device 1 is a sophisticated mask like those used in special effects makeup for a young actor to play a role of an old man in movies and made of thin silicone resembling human skin in appearance. Therefore, it is difficult for a human to visually judge whether such a disguising mask is worn.
      First, the principle of disguising mask detection by the disguising mask detecting device 1 will be described. FIG. 1 is a graphical presentation showing the spectra of luminances of reflected light when light is emitted at objects. In this figure, the dotted line presents the spectrum of reflected light of light emitted at human skin. On the other hand, the solid line presents the spectrum of reflected light of light emitted at silicone. Here, the luminance indicates the degree of brightness.
      In this figure, the luminance of reflected light of light emitted at silicone abruptly falls in a wavelength range around 1140 nm to 1220 nm marked by hatched lines, which is an infrared wavelength band, and is obviously different from the luminance of reflected light of light emitted at human skin. Here, an abrupt fall occurs because the silicone absorbs light in the wavelength range marked by the hatched lines well and weakens the reflected light.
      The disguising mask detecting device 1 utilizes the above difference in spectrum of luminance of reflected light between silicone and human skin, and detects a disguising mask depending on whether an abrupt fall occurs in the wavelength range marked by the hatched lines.
      Subsequently, the configuration of the disguising mask detecting device 1 will be described. The disguising mask detecting device 1 comprises, as shown in FIG. 2, a light source 11, a camera 12, a speaker 13, a liquid crystal monitor 14, an operator 15, an external storage 16, and a controller 17.
      The light source 11 is a halogen light source, is turned on/off based on instructions from the controller 17, and emits light at a person who is a subject. Here, the light source 11 may be a strobe or argon bulb. However, a halogen light source includes a lot of constituents in the infrared wavelength band and therefore is suitable for use as the halogen light source 11.
      Reflected light of the light emitted at a person by the light source 11 enters the camera 12. The camera 12 captures images of the reflected light in the visible light range, in a wavelength range of 1166±5 nm, in a wavelength range of 1190±5 nm, and in a wavelength range of 1214±5 nm all at once at the same time under the control of the controller 17.
      In the following explanation, the image in the visible light range captured by the camera 12 is also referred to as a visible light image; the image in the wavelength range of 1166±5 nm, an infrared image A; the image in the wavelength range of 1190±5 nm, an infrared image B; and the image in the wavelength range of 1214±5 nm, an infrared image C.
      The structure of the camera 12 is described here. The camera 12 comprises, as shown in FIG. 3, a lens 121, a beam splitter 122, filters 123 ( 123 A to 123 D) provided corresponding to the above-described wavelength ranges, and complementary metal oxide semiconductor devices (CMOSs) 124 ( 124 A to 124 D).
      The lens 121 collects the incident light. The beam splitter 122 is, for example, a prism or one way mirror and splits the light collected by the lens 121. The filters 123 transmit light in the corresponding wavelength ranges in the light split by the beam splitter 122. Specifically, the filters 123 A to 123 D transmit light in the wavelength range of 1166±5 nm, in the wavelength range of 1190±5 nm, in the wavelength range of 1214±5 nm, and in the visible light range, respectively.
      Moreover, the CMOSs 124 A to 124 D provided corresponding to the filters 123 A to 123 D convert light transmitted through the filters 123 A to 123 D to electric signals to create images in the corresponding wavelength ranges. Specifically, the CMOSs 124 A to 124 D create infrared images A to C and a visible light image, respectively. Here, image sensors such as charge-coupled devices (CCDs) may be used in place of the CMOSs 124.
      Returning to FIG. 2, the speaker 13 outputs sound based on control of the controller 17. The liquid crystal monitor 14 displays various kinds of information based on control of the controller 17. For example, when it is detected that a person is wearing a disguising mask, the controller 17 controls the speaker 13 to output a warning sound for giving notice accordingly and the liquid crystal monitor 14 to display a warning message.
      The operator 15 comprises various buttons and when the user conduct an operation, outputs a signal corresponding to the operation to the controller 17.
      The external storage 16 is, for example, a hard disc drive or the like, and serves as a temporal storage of images captured by the camera 12 and stores various data necessary for the mask detection procedure described later.
      The controller 17 is configured by a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and the like, and controls the entire disguising mask detecting device 1. The control procedure of the controller 17 is executed by, specifically, the CPU executing control programs stored in the ROM while using the RAM as the work area to temporarily store various data. The controller 17 functionally comprises an imaging controller 171, a face detector 172, a determiner 173, and a notifier 174.
      The imaging controller 171 controls turning-on/turning-off of the light source 11 and imaging operation of the camera 12 so as to acquire images of a person in the wavelength ranges (a visible light image and infrared images A to C).
      The face detector 172 analyzes the visible light image captured by the camera 12 and detects a face region of the person. Then, the face detector 172 detects in the face region a forehead region, a right cheek region, and a left cheek region, which are situated near face characteristic quantities (eyes, nose, mouth, and the like) and where the skin is exposed in a relatively large area.
      Here, the camera 12 captures the images of a person (a visible light image and infrared images A to C) all at once from the same point and at the same time. Therefore, the regions in the visible light image detected by the face detector 172 share the pixel positions with the regions in the other images (infrared images A to C) captured at the same time.
      Here, a known detection method can be used for the face detector 172 to detect the regions.
      For example, the face detector 172 applies the Sobel filter to the visible light image to detect outlines and extracts a face outline by face outline pattern matching. Then, the face detector 172 detects eyebrow outlines from above and an outline under the mouth from below within the extracted face outline and detects as a face region a region surrounded by the right and left ends of the face and the positions above the eyebrows and under the mouth. Then, the face detector 172 detects the black points corresponding to the eyeballs in the detected face region as the eye positions and specifies a forehead region, a right cheek region, and a left cheek region from the face region and eye positions based on general face statistical data. Here, the face detector 172 may detect face characteristic quantities such as the eyes, nose, and mouth by a known technique and when those characteristic quantities are detected, specify their neighboring regions as a forehead region, a right cheek region, and a left cheek region.
      Here, the above-described processing by the face detector 172 will be described using a specific example. For example, it is assumed that a visible light image as shown in FIG. 4A is given as the processing target of the face detector 172. In such a case, the face detector 172 detects a face region R 1 as shown in FIG. 4B. Moreover, the face detector 172 detects a forehead region R 2, a right cheek region R 3, and a left cheek region R 4 from the face region R 1.
      Returning to FIG. 2, the determiner 173 judges whether the luminances of the regions (the forehead region, right cheek region, and left cheek region) specified by the face detector 172 satisfy specific relations between the infrared images A to C that are different from relations exhibited by skin so as to judge whether there is an abrupt fall in the wavelength range marked by the hatched lines in FIG. 1 and determine whether the person is wearing a disguising mask.
      When the determiner 173 determines that a disguising mask is worn, the notifier 174 controls the speaker 13 and liquid crystal monitor 14 to give notice accordingly.
      Subsequently, the disguising mask detection procedure executed by the disguising mask detecting device 1 will be described. An immigration officer guides a person entering the country into the field angle of the camera 12 of the disguising mask detecting device 1 installed near an entry gate. In doing so, the officer conducts an operation to start the processing via the operator 15 of the mask detecting device 1. In response to the operation, the controller 17 of the mask detecting device executes the mask detection procedure shown in the flowchart of FIG. 5.
      Here, the disguising mask detecting device 1 may comprise a motion sensor and when the motion sensor detects a person entering the country, execute the mask detection procedure. Alternatively, with the camera 12 set in the live view mode, the mask detection procedure may be executed automatically when the controller 17 determines that a person is on camera.
      Moreover, a person wearing a disguising mask may become cautious when he sees the lens of the camera 12 or the like. Therefore, for example, a magic mirror may be placed in front of the camera 12 so that the mask detection procedure starts with an image captured unnoticeably.
      In the mask detection procedure of FIG. 5, first, the imaging controller 171 turns on the light source 11 and controls the camera 12 to acquire images of the person in the wavelength ranges (a visible light image and infrared images A to C) (Step S 11).
      Subsequently, the face detector 172 detects a face region from the acquired visible light image and detects a forehead region, a right cheek region, and a left cheek region from the face region (Step S 12).
      Subsequently, the determiner 173 compares the luminances of the regions (forehead region, right cheek region, and left cheek region) in the infrared images A to C acquired at the same time as the visible light image in the Step S 11 so as to execute the mask determination procedure to determine whether the person is wearing a disguising mask (Step S 13).
      Here, details of the mask determination procedure will be described with reference to the flowchart of FIG. 6.
      First, the determiner 173 selects one of the regions unselected in the ongoing mask determination procedure from among the detected forehead region, right cheek region, and left cheek region (Step S 131). The region selected in the Step S 131 is also referred to as the selected region hereafter.
      Subsequently, the determiner 173 selects one pixel from the selected region (for example, the pixel at the center of the selected region) and measures the luminance of the pixel in each of the infrared images A to C (Step S 132).
      Subsequently, the determiner 173 judges whether the measured luminances satisfy specific relations between the infrared images A to C (Step S 133). Specifically, the determiner 173 judges the luminance measured in the infrared image B is lower than the luminances measured in the infrared image A and infrared image C by a given rate. As a result, it is possible to judge whether there is an abrupt fall in luminance of reflected light in the silicone-specific wavelength range (the wavelength range around 1140 nm to 1220 nm shown in FIG. 1) that is not observed with human skin.
      Here, more specifically, the determiner 173 has only to judge whether the following relational expressions (1) to (3) are all satisfied in the Step S 133. Here, in the relational expressions (1) to (3), IA is the luminance measured in the infrared image A, IB is the luminance measured in the infrared image B, and IC is the luminance measured in the infrared image A. Moreover, T 1 to T 3 are coefficients and preset to numerical values optimum for the mask detection based on image capturing conditions.

           IA×T1 >IB  (1)
           IC×T2 >IB  (2)
           IC×T3 >IA  (3)
      If the above relational expressions (1) and (2) are satisfied, the luminance measured in the infrared image B is lower than the luminances measured in the infrared image A and infrared image C by a given rate. Moreover, if the above relational expression (3) is satisfied, the luminance measured in the infrared image C is higher than the luminance measured in the infrared image A by a given rate.
      If the measured luminances satisfy the specific relations (Step S 133; Yes), the determiner 173 measures, in each of the infrared images A to C, the luminances of eight pixels surrounding the pixel measured in the Step S 132 (Step S 134).
      Subsequently, the determiner 173 judges whether the measured luminances of the surrounding pixels also satisfy the specific relations between the infrared images A to C (Step S 135).
      If the luminances of the surrounding pixels also satisfy the specific relations (Step S 135; Yes), the determiner 173 determines that the person is wearing a disguising mask (Step S 136) and the mask determination procedure ends. Here, in the above-described mask determination procedure, it is determined that a disguising mask is worn when one pixel and eight pixels surrounding that pixel in any one of the selected regions (forehead, right cheek, and left cheek) all satisfy the specific relations. This is because a disguising mask is generally worn to cover the entire face and if an abrupt fall in luminance in the specific wavelength range is observed in any one of the selected regions, it is possible to determine that a disguising mask is worn without executing the mask determination procedure on the other selected regions.
      On the other hand, if the luminance of one pixel in the selected region does not satisfy the specific relations (Step S 133; No) or the luminances of the surrounding pixels do not satisfy the specific relations (Step S 135; No), the determiner 173 judges whether all of the forehead region, right cheek region, and left cheek region are selected in the ongoing mask determination procedure (Step S 137).
      If not all of the forehead region, right cheek region, and left cheek region are selected (Step S 137; No), the processing returns to the Step S 131 and the determiner 173 selects an unselected region and repeats a series of processing to judge whether the luminances of pixels in that region satisfy the specific relations so as to determine whether a disguising mask is worn.
      On the other hand, if all of the forehead region, right cheek region, and left cheek region are selected (Step S 137; Yes), the determiner 173 determines that the person is not wearing a disguising mask (Step S 138) and the mask determination procedure ends.
      Returning to FIG. 5, after the mask determination procedure (Step S 13) ends, the notifier 174 judges whether it is determined in the mask determination procedure that a disguising mask is worn (Step S 14). If a disguising mask is not worn (Step S 14; Yes), the disguising mask detection procedure ends.
      On the other hand, if a disguising mask is worn (Step S 14; Yes), the notifier 174 controls the speaker 13 and liquid crystal monitor 14 to give notice accordingly (Step S 15). As a result, the officer can notice the disguise of the person trying to pass through the entry gate, thereby preventing illegal entry. Then, the disguising mask detection procedure ends.
      As described above, the disguising mask detecting device 1 according to Embodiment 1 acquires (captures) images of a person in multiple different wavelength ranges and when the luminances of the face region satisfy specific relations between the acquired images that are different from relations exhibited by skin, judges that the person is wearing a disguising mask. In other words, the disguising mask detecting device 1 according to Embodiment 1 judges that a person is wearing a disguising mask when a concave shape is formed by connecting the luminances of the face region in the acquired images. As a result, highly accurate detection of a disguising mask with the use of the difference in spectrum of luminance of reflected light between silicone and human skin is made possible.
      Moreover, the disguising mask detecting device 1 according to Embodiment 1 detects characteristic regions where the skin is exposed in a relatively large area (forehead region, right cheek region, and left cheek region) from the face region in the acquired images and detects a disguising mask using the luminances of the characteristic regions. Therefore, the mask determination procedure does not need to be executed on the entire face region, whereby the mask detection processing load is reduced.
      Moreover, the disguising mask detecting device 1 according to Embodiment 1 judges whether a disguising mask is worn using not only the luminance of one pixel but also the luminances of pixels surrounding that pixel. Therefore, more accurate detection of a disguising mask is made possible.
      Moreover, the disguising mask detecting device 1 according to Embodiment 1 detects the presence/absence of a disguising mask with a camera using images in four different wavelength ranges (a visible light image and infrared images A to C), whereby detection of a disguising mask with a relatively small load is made possible.
      Moreover, the light source 11 of the disguising mask detecting device 1 according to Embodiment 1 is a halogen light source and therefore a sufficient amount of light in the infrared band can be obtained. Therefore, highly accurate detection of a disguising mask is made possible.

Embodiment 2

      Subsequently, a disguising mask detecting device 2 according to Embodiment 2 will be described. Here, as shown in FIG. 3, the disguising mask detecting device 2 is substantially the same in configuration of components as the disguising mask detecting device 1 according to Embodiment 1 and different only in the contents of the mask determination procedure.
      The mask determination procedure executed by the mask detecting device 2 will be described using the flowchart of FIG. 7. Here, as for the steps of which the contents are substantially the same as in the mask determination procedure shown in FIG. 6, their explanation will be simplified as appropriate. Moreover, the timing of starting the mask determination procedure in FIG. 7 is the same as in FIG. 6.
      As the mask determination procedure starts, first, the determiner 173 selects an unselected region from among the detected forehead region, right cheek region, and left cheek region (Step S 201), selects one pixel in the selected region and measures the luminance of the pixel in each of the infrared images A to C (Step S 202), and judges whether the measured luminances satisfy the specific relations between the infrared images A to C (Step S 203).
      If the luminances do not satisfy the specific relations between the infrared images A to C (Step S 203; No), the determiner 173 calculates a mask determination score of the selected region to be zero (Step S 204) and the processing advances to Step S 206.
      On the other hand, if the luminances satisfy the specific relations between the infrared images A to C (Step S 203; Yes), the determiner 173 measures, in each of the infrared images A to C, the luminances of pixels surrounding the pixel measured in the Step S 202 (for example, eight pixels neighboring the measured pixel). Then, the determiner 173 calculates the rate at which the luminances of the surrounding pixels satisfy the specific relations between the infrared images A to C as a score of the selected region (Step S 205), and the processing advances to the Step S 206. For example, if the luminances of all eight surrounding pixels satisfy the specific relations between the infrared images A to C, the score is calculated to be 1 ( 8/8). On the other hand, if the luminances of two of the eight surrounding pixels satisfy the specific relations between the infrared images A to C, the score is calculated to be 0.25 ( 2/8).
      In the Step S 206, the determiner 173 judges whether all of the forehead region, right cheek region, and left cheek region are selected. If not all of the forehead region, right cheek region, and left cheek region are selected (Step S 206; No), the processing returns to the Step S 201.
      If all of the forehead region, right cheek region, and left cheek region are selected (Step S 206; Yes), the determiner 173 calculates the average of the scores calculated for the regions as the final score (Step S 207). Then, the determiner 173 judges whether the final score is equal to or higher than a given threshold (for example, 0.5) (Step S 208).
      If the final score is equal to or higher than the threshold (Step S 208; Yes), the determiner 173 determines that the person is wearing a disguising mask (Step S 209). On the other hand, if the final score is lower than the threshold (Step S 208; No), the determiner determines that the person is not wearing a disguising mask (Step S 210). Then, the mask determination procedure ends.
      As described above, in the mask determination procedure of Embodiment 2, a disguising mask determination score is calculated for each of the right cheek region, left cheek region, and forehead region and it is determined whether a disguising mask is worn. Therefore, it is possible to detect a disguising mask with higher accuracy than the mask determination procedure of Embodiment 1 in which it is immediately determined that a disguising mask is worn when the luminances of any one of the regions (cheek region, right cheek region, and left cheek region) satisfy the specific relations.

Embodiment 3

      Subsequently, a disguising mask detecting device 3 according to Embodiment 3 will be described. Here, as shown in FIG. 3, the disguising mask detecting device 3 is substantially the same in configuration of components as the disguising mask detecting devices 1 and 2 according to Embodiments 1 and 2 and different only in the contents of the mask determination procedure.
      The mask determination procedure executed by the mask detecting device 3 will be described using the flowchart of FIG. 8. Here, as for the steps of which the contents are substantially the same as in the mask determination procedure shown in FIG. 6, their explanation will be simplified as appropriate. Moreover, the timing of starting the mask determination procedure in FIG. 8 is the same as in FIG. 6.
      As the mask determination procedure starts, first, the determiner 173 initializes a possible silicone counter and non-silicone counter used in disguising mask determination to zero (Step S 301).
      Subsequently, the determiner 173 selects one of the forehead region, right cheek region, and left cheek region (Step S 302). Then, the determiner 173 selects one of the unselected pixels in the selected region (Step S 303). The pixel selected in the Step S 303 is also referred to as the selected pixel hereafter.
      Subsequently, the determiner 173 measures the luminance of the selected pixel in each of the infrared images A to C (Step S 304). Then, the determiner 173 judges whether the measured luminances satisfy the specific relations between the infrared images A to C (Step S 305).
      If the measured luminances satisfy the specific relations (Step S 305; Yes), the determiner adds one to the possible silicone counter (Step S 306). On the other hand, if the measured luminances do not satisfy the specific relations (Step S 305; No), the determiner adds one to the non-silicone counter (Step S 307).
      Subsequently, the determiner 173 determines whether all pixels in the selected region are selected (Step S 308).
      If not all pixels are selected (Step S 308; No), the processing returns to the Step S 303 and the determiner 173 selects one pixel from the selected region and repeats the process to add one to the non-silicone counter or to the possible silicone counter based on the luminances of the pixel.
      On the other hand, if all pixels are selected (Step S 308; Yes), the determiner 173 judges whether all of the forehead region, right cheek region, and left cheek region are selected (Step S 309). If not all of the forehead region, right cheek region, and left cheek region are selected (Step S 309; No), the processing returns to the Step S 302.
      If all of the forehead region, right cheek region, and left cheek region are selected (Step S 309; Yes), in other words after the possible silicone counter or non-silicone counter is incremented for each of all pixels in the forehead region, right cheek region, and left cheek region, the determiner 173 judges whether the possible silicone counter has a higher value than the non-silicone counter (Step S 310).
      If the possible silicone counter has a higher value than the non-silicone counter (Step S 310; Yes), the determiner 173 determines that the person is wearing a disguising mask (Step S 311).
      On the other hand, if the possible silicone counter does not have a higher value than the non-silicone counter (Step S 310; No), the determiner 173 determines that the person is not wearing a disguising mask (Step S 312). Then, the disguising mask determination procedure ends.
      As described above, in the mask determination procedure of Embodiment 3, all pixels in the forehead region, right cheek region, and left cheek region are used to determine a disguising mask, whereby it is possible to detect a disguising mask with higher accuracy.
      Here, in the mask detection procedure of FIG. 8, it may be possible to use only the possible silicone counter and detect a mask based on whether the possible silicone counter has a value equal to or higher than a given value in the Step S 310. For example, with the given value set to 80% of all pixels in the forehead region, right cheek region, and left cheek region, it is possible to judge that a mask is worn when 80% or more of all pixels are of possible silicone.
      Moreover, in the mask detection procedure of FIG. 8, the possible silicone counter is increased by one in the Step S 306 when the luminances of the selected pixel satisfy the specific relations (Step S 305; Yes). However, it may be possible that when the luminances of the selected pixel satisfy the specific relations, it is determined as in Embodiment 1 whether the surrounding pixels satisfy the specific relations and only if satisfying, the possible silicone counter is increased by one.

Modified Embodiments

      The present disclosure is not confined to the above embodiments and needless to say, various changes can be made to the extent of not departing from the gist of the present disclosure.
      For example, the disguising mask detecting devices 1 to 3 according to the above-described embodiments eventually detect a disguising mask. However, the present disclosure is applicable to a detecting device detecting a thing to disguise attached to the skin, which is not necessarily a disguising mask.
      Moreover, in the disguising mask detecting devices 1 to 3 according to the above-described embodiments, the determiner 173 determines whether a person is wearing a disguising mask in the mask determination procedure. However, it may be possible that without the determination itself as to whether a disguising mask is worn, the determiner 173 determines only whether the luminances satisfy the specific relations between the infrared images and if satisfying, the notifier 174 gives notice accordingly.
      Moreover, the disguising mask detecting devices 1 to 3 shown in FIG. 2 are described on the assumption that the light source 11, camera 12, and the like are all integrated. Needless to say, they may be separated as appropriate. For example, the light source 11, camera 12, speaker 13, and the like may be separately prepared and combined with a device having the function of the controller 17 (for example, a PC or the like) to configure the disguising mask detecting devices 1 to 3. Alternatively, it may be possible that the function of the controller 17 is built in the camera 12 and the controller of the camera 12 works together with the light source 11, speaker 13, and the like as appropriate to configure the disguising mask detecting device 1.
      Moreover, in the above-described embodiments, it is determined that a disguising mask is worn when the luminances of an image in a wavelength range of 1166±5 nm (infrared image A), an image in a wavelength range of 1190±5 nm (infrared image B), and an image in a wavelength range of 1214±5 nm (infrared image C) satisfy the specific relations.
      However, the presence/absence of a disguising mask may be determined using images in other wavelength ranges as long as change in luminance of reflected light different from human skin can be detected. For example, obvious difference in spectrum of luminance of reflected light between silicone and human skin is observed in a wavelength range around 1500 nm to 1550 nm marked by a shaded area in FIG. 1. Therefore, it may be possible to prepare multiple filters for the wavelength range in the shaded area, acquire multiple images of a person, and determine the presence/absence of a disguising mask from the luminances of the face region. Moreover, images in the wavelength ranges both in the hatched area and in the shaded area may be used in the mask detection procedure and in such a case, the accuracy of detecting a mask can be improved.
      Moreover, in the above-described embodiments, the luminances of images in three wavelength ranges (infrared images A to C) are used to determine the presence/absence of a disguising mask. The luminances of images in three or more wavelength ranges may be used to determine the presence/absence of a disguising mask.
      Moreover, in the above-described embodiments, the face detector 172 detects a forehead region, a right cheek region, and a left cheek region from the face region, and the determiner 173 compares the luminances of the regions in the images to determine the presence/absence of a disguising mask. However, the face detector 172 does not need to detect all of a forehead region, right cheek region, and left cheek region, and has only to detect at least one region. For example, it may be possible that the face detector 172 detects only a forehead region and the determiner 173 compares only the luminances of the forehead region to determine the presence/absence of a disguising mask. Moreover, it may be possible that the face detector 172 detects a characteristic region other than the forehead region, right cheek region, and left cheek region and the luminances of that region are used to determine the presence/absence of a disguising mask. Moreover, it may be possible that the face detector 172 detects only a face region and the determiner 173 compares the luminances of the entire face region or a part thereof to determine the presence/absence of a disguising mask.
      Moreover, when the positions of the camera 12 and 13 and the point of photographing a person are fixed so that the face of the person definitely appears in a specific area of the image, the determiner 173 may compare the luminances of that specific area to determine the presence/absence of a disguising mask. In such a case, the disguising mask detecting devices 1 to 3 do not need to comprise the face detector 171.
      Moreover, in the above-described embodiments, as shown in FIG. 3, the camera 12 of the disguising mask detecting device 1 comprises the beam splitter 122 and multiple filters 123, whereby multiple images in different wavelength ranges can be captured at a time.
      However, the present disclosure is applicable even to a disguising mask detecting device 1′ comprising, as shown in FIG. 9, four cameras 18 ( 18 A to 18 D) capturing only an image in a single wavelength range in place of such a camera 12. Here, the cameras 18 A to 18 D each comprise a filter allowing light only in a wavelength range of 1166±5 nm, in a wavelength range of 1190±5 nm, in a wavelength range of 1214±5 nm, and in the visible light range, respectively, to transmit through the CMOS. Therefore, the cameras 18 A to 18 D can capture only infrared images A to D and a visible light image, respectively.
      Here, the external storage 16 of the disguising mask detecting device 1′ stores position parameters presenting the positional relations of the cameras 18 A to 18 D. The position parameters are information presenting, for example, the relative position coordinates (x, y, z), vertical angle (tilt), horizontal angle (pan), rotational angle (roll), and the like of the cameras 18 A to 18 D.
      In the disguising mask detecting device 1′, as shown in FIG. 9, the angles of reflected light from the person are different; therefore, the images in the wavelength ranges are not those captured at one and the same point. Then, when the luminances of a selected pixel in the infrared images A to C are measured in the mask determination procedure, the position of the pixel is not the same.
      Therefore, in the disguising mask detecting device 1′, the controller 17 comprises an image corrector 175 acquiring images in which the images captured by the multiple cameras 18 A to 18 D are corrected as if the person was photographed at one and the same point.
      For example, using a known technique, the image corrector 175 angularly-corrects the images captured at the positions of the cameras 18 B to 18 D so that they are at the same position as the image captured at the position of the camera 18 A with reference to the position parameters stored in the external storage 16. As a result, images sharing the pixel positions can be obtained. Then, the face detector 172 and determiner 173 can execute the mask detection procedure on the sharing images obtained by the image corrector 175.
      The disguising mask detecting device 1′ allows for use of cameras simpler in structure than the camera 12 of the disguising mask detecting device 1 using the beam splitter 122 and multiple filters 123 A to 123 D, whereby the disguising mask detecting device 1′ can inexpensively be configured.
      Moreover, the above-described embodiments are described using a case of detecting a disguising mask. Skin may be detected along with detection of a disguising mask. In such a case, relational expressions for detecting skin are obtained in advance and it is determined whether it is skin with the obtained relational expressions along with determination of whether the luminances of a selected pixel in the infrared images A to C satisfy the specific relations, whereby it is possible to detect whether the pixel is of silicone or of skin. Therefore, it is possible to determine whether a disguising mask is worn with higher accuracy.
      Moreover, in the disguising mask detecting devices 1 to 3 in the above-described embodiments, the filters 123 A to 123 D that are bandpass filters transmitting light in the wavelength ranges are used. This is not restrictive and other filters may be used. Images in desired wavelength ranges may be obtained by, for example, using a cutoff filter cutting off all infrared light in order to obtain a visible light image or combining multiple filters in order to obtain images in multiple different wavelength ranges in the infrared band (for example, combining a cutoff filter cutting off light of 1160 nm or shorter and a cutoff filter cutting off light of 1172 nm or longer in order to obtain an image in a wavelength range of 1166±5 nm).
      Moreover, the above-described embodiments are described using a case of installing the disguising mask detecting devices 1 to 3 in an immigration area. The place where the disguising mask detecting devices 1 to 3 are installed is not restricted to this. The bottom line is, the disguising mask detecting device 1 can be installed to detect a disguising mask where a disguising mask has to be detected. For example, the disguising mask detecting devices 1 to 3 may be installed for use near, evidently, a departure gate in an immigration area or at an entrance to a company or large-scale leisure facility.
      Moreover, in the above-described embodiments, the disguising mask detecting devices 1 to 3 detect a silicone disguising mask. The present disclosure can be used for detecting a disguising mask made of some other material. In such a case, it is necessary to acquire multiple images in wavelength ranges in which the spectrum of luminance of reflected light is largely different between the disguising mask material and human skin.
      For example, a resin mask exhibits high luminance in a wavelength range of 1480 to 1580 nm while human skin exhibits low luminance in this wavelength range. Moreover, a synthetic rubber mask exhibits extremely lower luminance in a wavelength range of 1480 to 1580 nm than human skin. Therefore, taking into account such difference between the skin and other material, it is possible to detect a resin or synthetic rubber mask.
      Moreover, it is possible to apply operation programs defining the operation of the disguising mask detecting devices 1 to 3 according to the above-described embodiments to an existing personal computer, information terminal device, or the like to allow the personal computer or the like to function as the disguising mask detecting devices 1 to 3 according to the present disclosure.
      Moreover, such programs are distributed by any method and, for example, may be saved and distributed on a non-transitory computer-readable recording medium such as a compact disk read only memory (CD-ROM), digital versatile disk (DVD), magneto-optical disk (MO), and memory card or distributed via a communication network such as the Internet.
      The foregoing describes some example embodiments for explanatory purposes. Although the foregoing discussion has presented specific embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention is defined only by the included claims, along with the full range of equivalents to which such claims are entitled.
      The above-described embodiments are entirely or partly, but not exclusively, described as in the following Supplementary Notes.

Supplementary Note 1

      A detecting device, comprising:

an image acquirer acquiring images in multiple different wavelength ranges of reflected light of light emitted at a person; and

a determiner determining whether luminances of a face region in the images acquired by the image acquirer satisfy specific relations different from relations exhibited by skin.

an image acquirer acquiring images in multiple different wavelength ranges of reflected light of light emitted at a person; and

a determiner determining whether luminances of a face region in the images acquired by the image acquirer satisfy specific relations different from relations exhibited by skin.

Supplementary Note 2

      The detecting device according to Supplementary Note 1, wherein

the determiner determines that the person is wearing a disguise when the specific relations are satisfied.

the determiner determines that the person is wearing a disguise when the specific relations are satisfied.

Supplementary Note 3

      The detecting device according to Supplementary Note 1 or 2, wherein

the image acquirer acquires multiple images in different wavelength ranges within an infrared band, and

the determiner determines that the specific relations are satisfied when a waveform presented by distribution of the luminances of the face region in the images is concave.

the image acquirer acquires multiple images in different wavelength ranges within an infrared band, and

the determiner determines that the specific relations are satisfied when a waveform presented by distribution of the luminances of the face region in the images is concave.

Supplementary Note 4

      The detecting device according to any one of Supplementary Notes 1 to 3, wherein

the image acquirer acquires images in wavelength ranges around 1166 nm, around 1190 nm, and around 1214 nm separately, and

the determiner determines that the specific relations are satisfied when the luminance of the face region in the image in the wavelength range around 1190 nm is lower than the luminances of the face region in the images in the wavelength ranges around 1166 nm and around 1214 nm by a given rate.

the image acquirer acquires images in wavelength ranges around 1166 nm, around 1190 nm, and around 1214 nm separately, and

the determiner determines that the specific relations are satisfied when the luminance of the face region in the image in the wavelength range around 1190 nm is lower than the luminances of the face region in the images in the wavelength ranges around 1166 nm and around 1214 nm by a given rate.

Supplementary Note 5

      The detecting device according to any one of Supplementary Notes 1 to 3, wherein

the image acquirer acquires images in wavelength ranges around 1166 nm, around 1190 nm, and around 1214 nm, and

the determiner determines that the specific relations are satisfied when the luminance of the face region in the image in the wavelength range around 1190 nm is lower than the luminances of the face region in the images in the wavelength ranges around 1166 nm and around 1214 nm by a given rate and the luminance within the face region in the image in the wavelength range around 1214 nm is higher than the luminance of the face region in the image in the wavelength range around 1166 nm by a given rate.

the image acquirer acquires images in wavelength ranges around 1166 nm, around 1190 nm, and around 1214 nm, and

the determiner determines that the specific relations are satisfied when the luminance of the face region in the image in the wavelength range around 1190 nm is lower than the luminances of the face region in the images in the wavelength ranges around 1166 nm and around 1214 nm by a given rate and the luminance within the face region in the image in the wavelength range around 1214 nm is higher than the luminance of the face region in the image in the wavelength range around 1166 nm by a given rate.

Supplementary Note 6

      The detecting device according to any one of Supplementary Notes 1 to 5, comprising:

a face detector detecting a face region of the person from the images acquired by the image acquirer,

wherein the determiner determines whether the luminances of the face region detected by the face detector satisfy the specific relations.

a face detector detecting a face region of the person from the images acquired by the image acquirer,

wherein the determiner determines whether the luminances of the face region detected by the face detector satisfy the specific relations.

Supplementary Note 7

      The detecting device according to Supplementary Note 6, wherein

the face detector detects a characteristic region from the face region, and

the determiner determines whether the luminances of the characteristic region in the images detected by the face detector satisfy specific relations.

the face detector detects a characteristic region from the face region, and

the determiner determines whether the luminances of the characteristic region in the images detected by the face detector satisfy specific relations.

Supplementary Note 8

      The detecting device according to Supplementary Note 7, wherein

the face detector detects at least one of a forehead region, right cheek region, and left cheek region as the characteristic region.

the face detector detects at least one of a forehead region, right cheek region, and left cheek region as the characteristic region.

Supplementary Note 9

      The detecting device according to any one of Supplementary Notes 1 to 8, wherein

the image acquirer acquires the images in multiple different wavelength ranges by splitting reflected light of the light emitted at the person.

the image acquirer acquires the images in multiple different wavelength ranges by splitting reflected light of the light emitted at the person.

Supplementary Note 10

      The detecting device according to any one of Supplementary Notes 1 to 8, wherein

the image acquirer comprises:

multiple image capturers provided at different positions for each of the specific wavelength ranges and capturing images in corresponding wavelength ranges; and

an image corrector acquiring images in which the images captured by the multiple image capturers are corrected as if the person was photographed at one and the same point.

the image acquirer comprises:

multiple image capturers provided at different positions for each of the specific wavelength ranges and capturing images in corresponding wavelength ranges; and

an image corrector acquiring images in which the images captured by the multiple image capturers are corrected as if the person was photographed at one and the same point.

Supplementary Note 11

      The detecting device according to any one of Supplementary Notes 1 to 10, wherein

the determiner further comprises a notifier giving notice of the specific relations being satisfied when determined so.

the determiner further comprises a notifier giving notice of the specific relations being satisfied when determined so.

Supplementary Note 12

      The detecting device according to any one of Supplementary Notes 1 to 11, wherein

the light emitted at the person is infrared light emitted from a halogen light source.

the light emitted at the person is infrared light emitted from a halogen light source.

Supplementary Note 13

      The detecting device according to Supplementary Note 2, wherein

the disguise is a disguise with a silicone disguising mask.

the disguise is a disguise with a silicone disguising mask.

Supplementary Note 14

      A detecting method, comprising:

an image acquisition step of acquiring images in multiple different wavelength ranges of reflected light of light emitted at a person; and

a determination step of determining whether luminances of a face region in the images acquired in the image acquisition step satisfy specific relations different from relations exhibited by skin.

an image acquisition step of acquiring images in multiple different wavelength ranges of reflected light of light emitted at a person; and

a determination step of determining whether luminances of a face region in the images acquired in the image acquisition step satisfy specific relations different from relations exhibited by skin.

Supplementary Note 15

      A non-transitory recording medium saving a program that allows a computer to function as:

a determiner determining whether luminances of a face region in images of a person captured in multiple different wavelength ranges satisfy specific relations different from relations exhibited by skin.

a determiner determining whether luminances of a face region in images of a person captured in multiple different wavelength ranges satisfy specific relations different from relations exhibited by skin.

INDUSTRIAL APPLICABILITY

      The present disclosure is preferably used for determining whether a person entering a country is disguising in an immigration area.

REFERENCE SIGNS LIST

1, 2, 3, 1′ Disguising mask detecting device

11 Light source

12, 18 (18A to 18D) Camera

121 Lens

122 Beam splitter

123 (123A to 123D) Filter

124 (124A to 124D) CMOS

13 Speaker

14 Liquid crystal monitor

15 Operator

16 External storage

17 Controller

171 Imaging controller

172 Face detector

173 Determiner

174 Notifier

175 Image corrector