Optical measurement device

Abstract

To provide an optical measurement device capable of capturing a reflection-free sharp image by the use of imaging information on other light sources even in a situation in which reflected light of one light source causes reflection onto an object to be measured.SOLUTION: An optical measurement device comprises: a second light source 12 which irradiates an object X to be measured, receiving first irradiation light L1 that a first source 11 emits, with predetermined second irradiation light L2; an imaging part 20 which images a first state in which the object X to be measured is not irradiated with the second irradiation light L2 and a second state in which the object is irradiated with the second irradiation light L2; and a control part 30 which performs image processing with imaging information captured by the imaging part 20. The control part 30 computes and outputs difference information between first imaging information captured in the first state and second imaging information captured in the second state.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a light measurement device that provides a desired image to a person to be measured by using a plurality of light sources. [Background technology]

[0002] As a technique for capturing an image using a plurality of light sources, for example, the techniques shown in Patent Documents 1 to 3 are disclosed. The technique shown in Patent Document 1 includes a plurality of light source units that irradiate light from different directions, an image reading unit that obtains a plurality of read images by reading the read object irradiated with light from a plurality of directions, a gloss detection means that executes a gloss detection process to detect the presence or absence of gloss by comparing an average value of the luminance value for each region into which the read image is divided with a threshold value previously set for each region, a luminance correction means that executes a luminance correction for one read image so that the luminance value of the white background portion becomes a maximum value when it is determined that there is no gloss, and executes a luminance correction for the plurality of read images so that the luminance value of the white background portion becomes a maximum value when it is determined that there is gloss, and an image synthesis means that synthesizes regions that are predetermined to have a small change in image level due to specular reflection light for the plurality of read images that have been subjected to the luminance correction, and generates a corrected read image corresponding to the read object.

[0003] The technology disclosed in Patent Document 2 includes a light output unit that outputs light including a first wavelength and a second wavelength different from the first wavelength, a light receiving element that receives reflected light, an intensity acquisition unit that acquires a first intensity of first reflected light of the first light including the first wavelength and not including the second wavelength, a second intensity of second reflected light of second light including the second wavelength and not including the first wavelength, and a third intensity of third reflected light of third light including the first wavelength and the second wavelength, an intensity calculation unit that calculates a complementary first intensity from the difference between the third intensity and the second intensity and calculates a complementary second intensity from the difference between the third intensity and the first intensity, and a biometric information detection unit that determines biometric information of an object using the complementary first intensity and the complementary second intensity.

[0004] In addition, a technology for acquiring information on a subject by measuring a change in the polarization state of measurement light from the subject is disclosed in Patent Document 3. In the technology shown in Patent Document 3, a light measurement device is composed of a polarized irradiation unit that irradiates the subject with irradiation light with controlled polarization, and a polarization imaging unit that images the polarization state of the measurement light generated by scattering, reflecting, absorbing, etc. of the irradiation light by the subject, calculates all or a part of the Stokes parameters of the measurement light, and measures the change in the polarization component generated between the irradiation light and the measurement light by the subject, and since the subject is irradiated with irradiation light with a controlled polarization state, it is possible to acquire subject information that is difficult to measure when natural light, i.e., non-polarized irradiation light, is irradiated to the subject, and it is also possible to suppress noise and contrast reduction that occur when measuring polarization by irradiating the subject with irradiation light with an unstable polarization state. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-7034 A [Patent Document 2] JP 2016-29351 A [Patent Document 3] JP 2022-164561 A Summary of the Invention [Problem to be solved by the invention]

[0006] Here, for example, in remote monitoring, the scale of an analog instrument is imaged and the image is read by a monitor in a remote location. However, there are cases where light is reflected on the scale cover of the analog instrument, making it impossible to read the scale or pointer inside the cover in the image.

[0007] There is a problem in that no effective technology capable of solving such problems, including the above-mentioned conventional technology, has been developed.

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide a light measurement device that can capture a clear image without reflections by using imaging information from other light sources, even in a situation where reflections from one light source occur on the object to be measured. [Means for solving the problem]

[0009] The light measurement device of the present invention includes a second light source that irradiates a predetermined second irradiation light onto a measurement object receiving a first irradiation light emitted by a first light source, an imaging means that images a first state in which the second irradiation light is not irradiated onto the measurement object, and a second state in which the second irradiation light is irradiated onto the measurement object, and an image processing means that performs image processing on the imaging information captured by the imaging means, and the image processing means calculates and outputs difference information between the first imaging information captured in the first state and the second imaging information captured in the second state.

[0010] In this way, in the light measurement device according to the present invention, a predetermined second irradiation light is irradiated from a second light source onto a measurement object receiving a first irradiation light emitted from a first light source, an imaging means images each of a first state in which the second irradiation light is not irradiated onto the measurement object, and a second state in which the measurement object is irradiated with the second irradiation light, and an image processing means performs image processing on the imaging information captured by the imaging means, and the image processing means calculates and outputs difference information between the first imaging information captured in the first state and the second imaging information captured in the second state. Therefore, even in a case in which light from a first light source such as sunlight is reflected on the measurement object, it is possible to obtain imaging information of a state in which only the second irradiation light from the second light source is irradiated by calculating the difference between the imaging information captured in that state (first state) and the imaging information captured in a state in which the second irradiation light from the second light source is irradiated, thereby achieving the effect of outputting a clear image without reflections. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing a configuration of a light measurement device according to a first embodiment. [Diagram 2] FIG. 13 is a diagram showing an example of an image obtained when an object to be measured is captured in a state where a reflection is present; [Diagram 3] 13 is a diagram showing an example of an image captured when the measurement object is not illuminated with a second light source. FIG. [Figure 4] 4 is a diagram showing an example of an output image when a difference between the image in FIG. 2 and the image in FIG. 3 is obtained by image processing. FIG. [Diagram 5] 5 is a diagram showing an example of an arrangement condition of a second light source in the light measurement device according to the first embodiment. FIG. [Figure 6] 5 is a diagram showing an example of an arrangement condition of a second light source and an imaging unit in the light measurement device according to the first embodiment. FIG. [Figure 7] This is a diagram of the experimental setup to investigate the effect of polarization change due to scattering on PPPI (Polarization - Probe Polarization - Imaging). [Figure 8] FIG. 8 is a diagram showing the surface structures of the two pieces of ground glass used in the experiment of FIG. 7. [Figure 9] This is an image of the degree of polarization obtained in the experiment of Figure 7. [Figure 10] FIG. 8 is a schematic diagram of PPPI near the subject when the glass plate in the experiment in FIG. 7 is replaced with a wave plate. [Figure 11] This is an image of the degree of polarization obtained in the experiment of Figure 10. [Figure 12] FIG. 8 is a schematic diagram of PPPI near the subject when the glass plate in the experiment of FIG. 7 is replaced with a patterned waveplate. [Figure 13] 13 is an image of the degree of polarization obtained in the experiment of FIG. 12. [Figure 14] FIG. 13 is a diagram showing an experimental optical system for verifying whether PPPI can be used to reduce external light reflections and capture images of instrument characters with emphasis. [Figure 15] This is a photo of the exterior of the instrument with external light reflected. [Figure 16] FIG. 1 is a diagram showing the principle of using polarized illumination in PPPI measurement to reduce instrument glare. [Figure 17]13A and 13B are luminance images obtained before and after reducing external light reflection using a light measurement device according to a second embodiment. [Figure 18] FIG. 18 is a diagram showing the result of converting the image in FIG. 17 into a DoP image. [Figure 19] FIG. 13 is a diagram showing the results of observing the surface structure of the character portion and the dial portion of an instrument using a laser microscope. [Figure 20] FIG. 13 is a diagram showing the results of measuring the degree of polarization and the degree of circular polarization of the central part of an instrument image obtained by illuminating the instrument with polarized light at wavelengths of 532 nm and 980 nm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (First embodiment of the present invention) The light measurement device according to the present embodiment will be described with reference to Figures 1 to 6. The light measurement device according to the present embodiment can reduce reflections and obtain clear imaging information even in a situation where light from a first light source is reflected by an imaging target and reflected on the imaging target when imaging the imaging target.

[0013] Fig. 1 is a diagram showing the configuration of a light measurement device according to this embodiment. In Fig. 1, the light measurement device 1 includes a second light source 12 that irradiates a measurement object X in a state where a first irradiation light L1 from a first light source 11 is irradiated with a second irradiation light L2 having a predetermined optical characteristic, an imaging unit 20 that captures images of a first state in which the second light source 12 does not irradiate the measurement object X with the second irradiation light L2 and a second state in which the second light source 12 irradiates the measurement object X, a control unit 30 that controls the second light source 12 and the imaging unit 20, and a display unit 40 that displays imaging information captured by the imaging unit 20.

[0014] In this embodiment, the first irradiation light L1 of the first light source 11 corresponds to, for example, sunlight from the sun outdoors, or illumination light from a fluorescent lamp or the like indoors. The measurement object X is, for example, one whose surface is mirror-finished and has a high reflectance of the first irradiation light L1, and specifically corresponds to the scale display of an analog instrument, the display of an analog clock, and the like.

[0015] When the imaging unit 20 images the measurement object X while the first irradiation light L1 is irradiated onto the measurement object X, the first irradiation light L1 reflected from the measurement object X may be reflected depending on the position of the sun or lighting, which is the first light source 11, and the imaging angle (imaging direction) of the imaging unit 20, making it impossible to recognize the imaged content. In particular, when monitoring an analog instrument remotely, the imaging information captured by the imaging unit 20 is recognized by an AI or the like, but the first irradiation light L1 is reflected by the mirror-finished cover of the analog instrument, and the first irradiation light L1 is reflected. As a result, the dial, pointer, etc. inside the cover become difficult to see, and a situation occurs in which image recognition is impossible. In this embodiment, such a problem is solved by performing the following processing.

[0016] The second light source 12 is a light source that irradiates the measurement object X with second irradiation light L2 having optical characteristics different from the first irradiation light L1 of the first light source 11, and the imaging unit 20 is an imaging element that images the measurement object X. The control unit 30 controls the operations of the second light source 12 and the imaging unit 20, and in an environment in which the measurement object X is irradiated with the first irradiation light L1, turns the driving of the second light source 12 ON / OFF (ON is the second state, and OFF is the first state), and images the measurement object X by the imaging unit 20 in response to the ON / OFF. The captured image is subjected to image processing by the control unit 30 and displayed on a display unit 40 such as a display.

[0017] 2 to 4 are diagrams showing examples of captured images, in which FIG. 2 is a diagram showing an example of an image when the measurement object X is imaged in a second state in which the second irradiation light L2 is irradiated with a state in which the first irradiation light L1 is reflected, FIG. 3 is a diagram showing an example of an image when the measurement object X is imaged in a first state in which the second irradiation light L2 is not irradiated with a state in which the first irradiation light L1 is reflected, and FIG. 4 is a diagram showing an example of an output image when the difference between the image in FIG. 2 and the image in FIG. 3 is obtained by image processing.

[0018] In the image of Fig. 2, the measurement object X is irradiated with the first irradiation light L1, and a reflection region R is generated by this first irradiation light L1. In this state, the image is captured by the imaging unit 20 in a second state in which the second irradiation light L2 is further irradiated by the second light source 12. In Fig. 2, the reflected light of the first irradiation light L1 is represented by hatching at 135°, and the reflected light of the second irradiation light L2 is represented by hatching at 45°. The reflection region R makes it very difficult to read the scale of the instrument.

[0019] The image in Fig. 3 is an image captured by the imaging unit 20 when the control unit 30 turns off the second light source 12 and transitions from the second state in Fig. 2 to the first state, in which the measurement object X is irradiated with the first irradiation light L1 and a reflection region R is generated by this first irradiation light L1. As in the case of Fig. 2, the reflected light of the first irradiation light L1 is represented by hatching at 135°.

[0020] The image in FIG. 4 is a difference image between the image in FIG. 3 and the image in FIG. 2 extracted by the control unit 30 through image processing. Since it is a difference between the image in FIG. 3 and the image in FIG. 2, the reflected light (135° hatching) of the first irradiation light L1 and the reflection area R common to FIG. 2 and FIG. 3 are eliminated, and only the image represented by the reflected light (45° hatching) of the second irradiation light L2 is extracted. As shown in FIG. 4, by eliminating the reflection area R, it is possible to obtain a clear image by the reflected light of the second irradiation light L2. Note that the result of actually obtaining the image in FIG. 4 from the image in FIG. 2 using the light measurement device 1 according to this embodiment is shown in FIG. 17 in the second embodiment described later. It is clear from the image in FIG. 17 that the reflection due to external light is reduced and the character part of the instrument can be read.

[0021] In the device configuration of Fig. 1, if the imaging angle of the imaging unit 20 satisfies the total reflection condition of the second irradiation light L2, the second irradiation light L2 will be totally reflected by a cover of an analog instrument or the like, and an image as shown in Fig. 4 will not be obtained. Therefore, as shown in Fig. 5, it is desirable that the second light source 12 irradiates the second irradiation light L2 at an angle at which the second irradiation light L2 is not totally reflected by the surface of the measurement object X. In other words, it is desirable that the second light source 12 is disposed so that the second irradiation light L2 is irradiated at an angle at which the angle α between the normal vector of the surface of the measurement object X and the second irradiation light L2 is less than the critical angle.

[0022] Furthermore, if the second irradiation light L2 is reflected by the cover of an analog instrument or the like and the reflected light is directly incident on the imaging unit 20, the second irradiation light L2 will be reflected in the image of the imaging unit 20. Therefore, as shown in Fig. 6, it is desirable to arrange the imaging direction of the imaging unit 20 and the optical path of the reflected light of the second irradiation light L2 in a different position. That is, it is desirable to arrange the second light source 12 and the imaging unit 20 so that the angle a between the normal vector of the surface of the measurement object X and the second irradiation light L2 and the angle b between the normal vector of the surface of the measurement object X and the axis that is the imaging direction are a ≠ b.

[0023] In this manner, in the light measurement device according to the present embodiment, the second light source 12 irradiates the measurement object X receiving the first irradiation light L1 emitted by the first light source 11 with a predetermined second irradiation light L2, the image capturing unit 20 captures images of the measurement object X in a first state in which the measurement object X is not irradiated with the second irradiation light L2, and in a second state in which the measurement object X is irradiated with the second irradiation light L2, and the control unit 30 performs image processing on the imaging information captured by the imaging unit 20, and calculates and outputs a difference image between the image captured in the first state and the image captured in the second state. Therefore, even in a case in which the light of the first light source 11, such as sunlight, is reflected on the measurement object X, it is possible to obtain imaging information of a state in which only the light of the second light source 12 is irradiated by calculating the difference between the imaging information captured in that state (first state) and the imaging information captured in a state in which the second irradiation light L2 of the second light source 12 is irradiated (second state), and a clear image without reflections can be output.

[0024] Furthermore, by positioning the second light source 11 so that it does not satisfy the total reflection condition with respect to the measurement object X, or by positioning the second irradiation light L2 so that the reflected light is not directly received by the projection unit 20, a clear image without reflections caused by the first light source 11 can be reliably obtained.

[0025] (Second embodiment of the present invention) The light measurement device 1 according to this embodiment will be described with reference to Fig. 7 to Fig. 20. In the light measurement device 1 according to this embodiment, the second irradiation light L2 of the second light source 12 is irradiation light with controlled polarization, and an imaging unit 20 captures an image of the polarization state of the measurement light generated by irradiating the measurement object X with the second irradiation light L2. Note that descriptions of this embodiment that overlap with those of the first embodiment will be omitted.

[0026] After being irradiated to a material, the polarization of the electromagnetic waves reflected, scattered, and transmitted through it contains information such as the surface shape and anisotropy of the material, and by capturing a polarized image of the irradiated object, information such as surface scratches and residual stress can be visualized non-contact and non-destructively. For this reason, interest in polarization imaging has been increasing in recent years, and as shown in Patent Document 3 above, a technology called Polarization-probe polarization-imaging (PPPI) (Reference 1: M. Sakamoto et.al., Sci. Rep. 12, 15268 (2022).) that captures the spatial distribution of polarization under polarized illumination is known. Unlike general polarization imaging methods under unpolarized illumination, this method can be affected by the effects of many elements of the Mueller matrix, making it possible to visualize a lot of subject information such as anisotropy and optical rotation. Furthermore, by using polarization separation by a polarization diffraction grating for polarization imaging, polarization imaging can be performed with a high extinction ratio even in the infrared region. In a previous study, PPPI was demonstrated from the visible range to the near infrared range, and it was shown that it is possible to visualize the anisotropy of a birefringent medium under circularly polarized illumination. The light measurement device according to this embodiment uses this PPPI to reduce the effect of glare caused by the first irradiation light L1 from the first light source 11.

[0027] First, the following investigation was carried out on the effects of differences in the polarization state and wavelength of polarized illumination on polarization exploration type polarimetry for subjects with light scattering.

[0028] (Light Scattering PPPI) Light scatterers can be broadly divided into Rayleigh scattering, when the particle size is small compared to the wavelength of the irradiated light, Mie scattering, when the particle size is large, and diffractive scattering. Of these, Rayleigh scattering and Mie scattering can be factors that can change polarization in isotropic media. First, in order to investigate the effect of polarization changes due to scattering on PPPI, two pieces of frosted glass (grid number), a glass plate, and a mirror were arranged in series as shown in Figure 7, and PPPI was performed.

[0029] The light source used was LEDs with three wavelengths, 532 nm, 980 nm, and 1550 nm. The polarization of the irradiated light was converted to 90° linear polarization (90LP) or right circular polarization (RCP) using a polarizer and a quarter-wave plate, and then irradiated onto the subject. The angle of incidence of the light with respect to the surface normal vector of the ground glass was 15°, and a polarization imaging device was installed in the surface normal direction of the ground glass. The polarization imaging device used a polarization camera using a polarization diffraction grating as shown in Reference 1. Figures 8(A) and 8(B) show the surface structures of two pieces of ground glass observed with a laser microscope. From these results, it can be seen that the ground glass surface has a mixture of large uneven structures on the order of several tens of μm and fine uneven structures on the order of several tens of nm, and that this is a sample in which all of Rayleigh scattering, Mie scattering, and diffractive scattering can occur simultaneously. Images of the degree of polarization (DoP) obtained as a result of PPPI are shown in Figures 9(A) and 9(B). Figure 9(A) shows the results when 90LP is irradiated, and Figure 9(B) shows the results when RCP is irradiated. It can be seen that the decrease in polarization degree is greater when RCP is irradiated than when 90LP is irradiated, and the decrease in polarization degree is smaller as the wavelength of the irradiated light becomes longer. Since the decrease in DoP is mitigated as the wavelength becomes longer, it can be inferred that the effect of Rayleigh scattering, in which the scattering strength is inversely proportional to the fourth power of the wavelength, contributes greatly to depolarization.

[0030] (PPPI of anisotropic medium hidden behind light scatterers) From the above experimental results, it is expected that the effect of light scattering can be suppressed by using long wavelength light for polarized illumination, and therefore it is possible to visualize anisotropy hidden behind scattering bodies by selecting the appropriate wavelength. Therefore, the glass plate in Fig. 7 was replaced with a wave plate or a patterned wave plate (q-plate: QP) and PPPI was performed again. Figure 10 shows a schematic diagram of the vicinity of the subject in PPPI when a wave plate is inserted between the frosted glass and the mirror, and Figs. 11(A) and (B) show DoP images obtained by the measurement in Fig. 10. Fig. 11(A) shows the case where 90LP was irradiated, and Fig. 11(B) shows the case where RCP was irradiated. It can be seen that the DoP is reduced more than the results in Fig. 9 for the glass plate. This phenomenon is believed to be due to the following mechanism.

[0031] First, the light incident on the ground glass is converted into scattered light with wave vectors in various directions by the ground glass. The scattered light then passes through a wave plate and is converted into a different polarization state for each wave vector component. This results in a complex spatial distribution of polarization. In polarization measurement in imaging, when different polarization states are simultaneously imaged within a single pixel, this leads to a decrease in the degree of polarization. This is thought to be the result of the decrease in the degree of polarization. In addition, by comparing Figures 11(A) and 11(B), it can be confirmed that the decrease in the degree of polarization is more significant for RCP than for 90LP, as in the case of an isotropic medium placed behind the ground glass as in Figure 9.

[0032] Next, PPPI was performed with the anisotropic medium as a patterned wave plate, QP. Figure 12 shows a schematic diagram of the vicinity of the subject in PPPI when a patterned wave plate is inserted between the ground glass and the mirror, and Figures 13(A) and (B) show images of DoP, azimuth angle, and ellipticity angle obtained in the measurement of Figure 12, respectively. Figure 13(A) shows the case where 90LP was irradiated, and Figure 13(B) shows the case where RCP was irradiated. As in the case of the wave plate in Figures 10 and 11, a large decrease in DoP is observed compared to the result of the glass plate in Figure 9. In addition, when 90deg linearly polarized light was irradiated, a fan-shaped polarization distribution was observed. This can be interpreted as follows.

[0033] First, because QP has a radial optical axis distribution, when irradiated with 90LP, there are regions where the light is converted to elliptically polarized light and regions where the light remains almost unchanged from linear polarization (the polarization becomes more elliptical at positions where the optical axis of QP and the polarization azimuth angle form 45 deg.). From the results of Figures 11(A) and (B), it is considered that the polarization degradation occurs more significantly in regions where the light is converted to a polarization state closer to circular polarization.

[0034] When irradiating with RCP, the light is converted into elliptically polarized light with the same ellipticity angle regardless of the distribution of the optical axis of the QP, so no spatial distribution is observed in the decrease in the degree of polarization. In addition, in the image captured at the azimuth angle reflecting the optical axis distribution of the QP, it can be seen that a clear azimuth angle distribution can be imaged even through a strong light scattering plate when irradiated with RCP, where the optical axis direction is reflected in the polarization azimuth angle with high sensitivity even with a slight effect of birefringence, at a long wavelength where the effect of light scattering is reduced. From the above results, it is expected that the anisotropic structure of a subject hidden behind a light scattering body can be visualized more clearly by selecting long wavelength and circularly polarized illumination.

[0035] (PPPI of instruments with reflections (surface microstructure)) Taking advantage of the feature of PPPI measurement that uses polarized irradiation, we explain below the method and demonstration of reducing the reflection of external light, and also verify whether PPPI is possible to capture emphasized images of the characters. Figure 14 shows the outline of the experimental optical system. A solar simulator was used as the light source for the reflection of external light (corresponding to the first light source 11). To generate external light (corresponding to the first irradiation light L1), white light emitted from the solar simulator was irradiated onto the box, creating a situation in which the image of the box was reflected onto the cover glass of the instrument (corresponding to the measurement target X). Figure 15 is a photograph of the appearance of the instrument with external light reflected. It can be seen that the strong white external light makes it impossible to read the characters on the instrument.

[0036] First, the principle of using polarized light illumination for PPPI measurement to reduce reflected light on instruments is shown in Figure 16. When an instrument with reflection is imaged using PPPI, an image is obtained in which (i) the image of the instrument caused by external ambient light (first illumination light L1), (ii) the image of the external light (first illumination light L1) reflected on the cover glass surface, and (iii) the image of the instrument caused by polarized light illumination (second illumination light L2) are superimposed. Here, if the polarized light illumination (second illumination light L2) of PPPI is blocked, the image obtained is a superposition of (i) and (ii). Therefore, if the images obtained with polarized light illumination (second illumination light L2) (corresponding to the second state) and without it (corresponding to the first state) are subtracted from each other, only the instrument image caused by polarized light illumination (second illumination light L2) (iii) remains, and the reflection of external light can be eliminated.

[0037] FIG. 17 shows the luminance images obtained before and after reducing the reflection of external light by the light measurement device 1 according to this embodiment. As explained in the first embodiment, the reflection of external light is reduced, and the character part of the instrument can be read. Furthermore, the result of conversion to a DoP image is shown in FIG. 18. It can be seen that the contrast between the character part and the dial part is improved compared to the luminance image in FIG. 17. In order to consider the reason for this, the result of observing the surface structure of the character part and the dial part of the instrument using a laser microscope is shown in FIG. 19. It can be seen that the character part has a rougher surface structure than the dial part, and is more strongly affected by light scattering. As mentioned above, the effect of light scattering causes a decrease in DoP, so it can be said that the difference in the intensity of light scattering due to the difference in surface structure contributed to the improvement of the contrast between the character part and the dial part in the DoP image. From the above, the method of differential processing of images with and without polarized light irradiation can be said to be an excellent method of reducing the reflection of external light, since it is possible to observe only the polarization change of the irradiated polarized light regardless of the observation position.

[0038] Furthermore, we investigated the difference in DoP images depending on the wavelength. We measured the DoP and degree of circular polarization (DoCP) images of the center of the instrument for each of the images of the instrument irradiated with polarized light at wavelengths of 532 nm and 980 nm. The results are shown in Figure 20. As in the results of Figure 18, the DoP of the instrument text area tends to be low and the DoP of the text area tends to be high at both wavelengths, and a similar trend can be seen for DoCP. Unlike the experiment using ground glass, in this case, a short wavelength (532 nm), where the effect of light scattering is more pronounced, tends to be advantageous in terms of high contrast imaging, but it can be seen that DoCP can obtain relatively high contrast images even with 980 nm irradiation. This is thought to be due to the fact that DoCP detects a pseudo degree of polarization that includes a change from circular polarization (decrease in ellipticity). What is possible with DoCP in visualization using the degree of polarization is that snapshots are possible without the need for LCR in the PPPI system, which is very advantageous for social implementation.

[0039] In addition, the wavelength of the polarized light irradiation of the PPPI in this embodiment is desirably set in the range of 355 nm to 1550 nm, taking into consideration the past production results of the polarizing diffraction grating and the corresponding wavelength of the liquid crystal retarder. [Explanation of symbols]

[0040] L1 1st irradiation light L2 2nd irradiation light R Reflection area X Measurement object 1. Light measuring device 11 1st light source 12 Second light source 20 Imaging unit 30 Control section 40 Display section

Claims

1. a second light source that irradiates a predetermined second irradiation light onto a measurement object receiving the first irradiation light emitted by the first light source; an imaging unit that images a first state in which the object to be measured is not irradiated with the second irradiation light and a second state in which the object to be measured is irradiated with the second irradiation light; image processing means for performing image processing using image information captured by the imaging means; The light measurement device, characterized in that the image processing means calculates and outputs difference information between first imaging information captured in the first state and second imaging information captured in the second state.

2. 2. The light measurement device according to claim 1, the second irradiation light emitted by the second light source is irradiation light whose polarization is controlled, The optical measurement device, wherein the imaging means images a polarization state of measurement light generated when the second irradiation light is irradiated onto the measurement object.

3. 3. The light measurement device according to claim 2, The light measurement device according to claim 1, wherein the second illumination light emitted by the second light source is circularly polarized light.

4. 4. The light measurement device according to claim 2, A light measuring device characterized in that the second irradiation light emitted by the second light source has a wavelength of 355 nm to 1550 nm.

5. 2. The light measurement device according to claim 1, the object to be measured is an instrument having at least a scale portion and a mirror-finished cover placed on the surface of the scale portion, The light measurement device according to claim 1, wherein the second illumination light emitted from the second light source is irradiated at an angle at which the second illumination light is not totally reflected by the surface of the cover.

6. 6. The light measurement device according to claim 5, a second light source and an imaging means arranged so that an angle of reflection of the second illumination light reflected by the cover is different from an imaging angle at which the imaging means images the instrument.

Images