Antifog property evaluating apparatus and antifog property evaluating method

There are provided an antifog property evaluating apparatus and an antifog property evaluating method capable of quantitatively and objectively evaluating an antifog property in a more realistic situation. The antifog property evaluating apparatus includes: fogging generation devices configured to generate the fogging of a surface of a sample; an object disposed at a position different from that of the sample; an imaging device configured to image the object via the sample; and an evaluation device configured to evaluate the antifog property of the sample on the basis of object images acquired by imaging the object.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and a method for evaluating antifog properties of window glasses, mirrors, or various lenses, for example.

2. Description of the Related Art

Evaluation on the antifog properties, which indicate tolerance to fogging, of window glasses, mirrors, or various lenses, for example, has been conducted in conventional techniques mainly by sensory tests by means of visual observation. Examples of such a sensory test include a breath antifog property test, a steam antifog property test, and a low-temperature antifog property test. In the breath antifog property test, a sample is breathed on to visually check the state of fogging in the sample. The antifog property of the sample is evaluated on a scale of about three to four levels on the basis of the presence or absence of fogging, the degree of blur in sight seen via transmission through the sample or reflection by the sample, etc. In the steam antifog property test, a sample is placed above hot water in a thermostatic bath to visually check the deposition state of water droplets on the sample. The antifog property of the sample is evaluated on a scale of about three to four levels on the basis of the presence or absence of the water droplets, the size of the water droplets, etc. In the low-temperature antifog property test, the presence or absence of fogging is evaluated on a scale of two levels when a sample cooled in a refrigerator or a freezer (for example, −20 to 5° C.) is brought back to a normal environment (for example, 20° C. and 65% RH). In these conventional sensory tests, however, evaluation greatly varies from person to person, and thus lacks in stability. Therefore, it has been difficult to evaluate the antifog property quantitatively and objectively.

In view of this, a method for objectively evaluating an antifog property by projecting an image of an object drawing a plurality of vertical lines or a grid on a sample in the above low-temperature antifog property test and measuring a condensation area (fogging area) on a surface of the sample on the basis of such vertical lines or grid, for example, has been proposed (see Patent Literature 1, for example). Also, a method for calculating an antifog property evaluation index on the basis of the degree of scattering of spot light projected on a sample to quantitatively and objectively evaluate the antifog property of the sample on the basis of the antifog property evaluation index has been proposed by the present applicants (see Patent Literature 2, for example).Patent Literature 1: Japanese Patent No. 3564085Patent Literature 2: Japanese Patent No. 5015183

SUMMARY OF THE INVENTION

In the evaluating method described in Patent Literature 1 above, however, the size of the condensation area can be evaluated quantitatively, but the degree of fogging, i.e., how much the generation of fogging has lowered the clearness (visibility) of sight seen through, for example, glass (via transmission or reflection) cannot be evaluated quantitatively and objectively. Therefore, in this method, sensory evaluation still needs to be conducted on the degree of fogging.

In the evaluating method described in Patent Literature 2 above, on the other hand, the antifog property evaluation index is calculated on the basis of the degree of scattering of spot light, thus allowing for the quantitative and objective evaluation of the antifog property taking the degree of fogging into account. In this method, however, since the antifog property is evaluated on the basis of the simplified phenomenon, the scattering of the spot light, it is difficult to have a mental image of the actual situation such as how a sight is seen through a car window or how a person's face shown on a bathroom mirror is seen, for example, from the evaluation result. Thus, there is a need for an evaluating method capable of quantitatively and objectively evaluating the antifog property in a more realistic situation.

The present invention has been made in view of the aforementioned problems. It is an object of the invention to provide an antifog property evaluating apparatus and an antifog property evaluating method capable of quantitatively and objectively evaluating an antifog property in a more realistic situation.

(1) An aspect of the present invention provides an antifog property evaluating apparatus including: a fogging generation device configured to generate fogging of a surface of a sample; an object disposed at a position different from that of the sample; an imaging device configured to image the object via the sample; and an evaluation device configured to evaluate an antifog property of the sample on the basis of an object image acquired by imaging the object.

(2) The antifog property evaluating apparatus described in (1) above may further include an image-adjusting lens optical system disposed between the sample and the object.

(3) The antifog property evaluating apparatus described in (1) or (2) above may further include a lighting device configured to illuminate the object with light from behind.

(4) The antifog property evaluating apparatus described in any one of (1) to (3) above may further include: a surface imaging lens optical system to be disposed between the sample and the imaging device; and a retracting device configured to retract the surface imaging lens optical system from an optical path.

(5) In the antifog property evaluating apparatus described in any one of (1) to (4) above, the evaluation device may derive an antifog property evaluation index of the sample on the basis of change in the object image when fogging is generated on the surface of the sample by the fogging generation device.

(6) In the antifog property evaluating apparatus described in (5) above, the evaluation device may derive the antifog property evaluation index on the basis of an area of a region where a pixel value is smaller than or equal to, or larger than or equal to, a predetermined threshold in the object image.

(7) In the antifog property evaluating apparatus described in (5) above, the evaluation device may derive the antifog property evaluation index on the basis of a rate of change in pixel values on a route set in the object image.

(8) In the antifog property evaluating apparatus described in (5) above, the evaluation device may derive the antifog property evaluation index on the basis of a difference or a ratio between pixel values at a first comparison point and a second comparison point in the object image.

(9) In the antifog property evaluating apparatus described in (5) above, the evaluation device may derive the antifog property evaluation index on the basis of a distance from a starting point to a goal point at which a pixel value first becomes larger than or equal to a predetermined threshold on a route set in the object image.

(10) In the antifog property evaluating apparatus described in (5) above, the evaluation device may derive the antifog property evaluation index on the basis of a compression ratio when the object image in an uncompressed state is compressed by a predetermined compression method or a file capacity after compression.

(11) In the antifog property evaluating apparatus described in (5) above, the evaluation device may derive the antifog property evaluation index on the basis of a histogram area of pixel values in the object image.

(12) Another aspect of the present invention provides an antifog property evaluating method including: a fogging generation step of generating fogging of a surface of a sample; an imaging step of imaging an object disposed at a position different from that of the sample via the sample; and an evaluation step of evaluating an antifog property of the sample on the basis of an object image acquired by imaging the object.

(13) In the antifog property evaluating method described in (12) above, an antifog property evaluation index of the sample is derived in the evaluation step on the basis of change in the object image when fogging is generated on the surface of the sample in the fogging generation step.

The antifog property evaluating apparatus and the antifog property evaluating method according to the present invention can provide an advantageous effect of an ability to quantitatively and objectively evaluate the antifog property in a more realistic situation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will now be described below with reference to the accompanying drawings.

An antifog property evaluating apparatus1according to an embodiment of the present invention will be described first.FIG. 1is a schematic diagram showing the antifog property evaluating apparatus1according to the present embodiment. As shown inFIG. 1, the antifog property evaluating apparatus1includes: a sample stage10on which a sample100is placed; a measuring chamber20configured to house the sample stage10; a steam spray device30connected to the inside of the measuring chamber20; an imaging device40disposed outside the measuring chamber20; a half mirror50disposed between the measuring chamber20and the imaging device40; a lighting device60disposed lateral to the half mirror50; an object70disposed between the lighting device60and the half mirror50; an image-adjusting lens optical system81disposed between the object70and the half mirror50; a surface imaging lens optical system82to be disposed between the half mirror50and the imaging device40; and a control device90configured to control the entire antifog property evaluating apparatus1.

The antifog property evaluating apparatus1according to the present embodiment generates the fogging of a surface101of the sample100by condensation and evaluates the antifog property of the sample100on the basis of an image acquired by imaging the object70via the fogged sample100(i.e., object image). In other words, the anti fog property evaluating apparatus1images light from the object70after being transmitted through the sample100or being reflected at the sample100, and evaluates the antifog property of the sample100on the basis of the resultant image of the object70.

The sample100is a window glass, a lens, or a mirror, for example, for which the antifog property is evaluated. The sample100has a plate shape cut out in an appropriate size. To accurately evaluate the antifog property of the sample100, the thickness of the sample100is preferred to be the same as the actual thickness. However, the thickness of the sample100is not limited thereto. In evaluating the antifog property of coating applied on a surface of a window glass, for example, an appropriate glass piece having a surface with the coating may be used as the sample100.

The sample stage10is a stand on which the sample100to be evaluated for its antifog property is placed. The sample stage10includes: a placement surface11on which the sample100is placed; a Peltier element12configured to cool the sample100; and a heat exchanger13configured to cool the heat generation side of the Peltier element12. A sample stage water circulator14configured to circulate cooling water is connected to the heat exchanger13.

In other words, the sample stage10is configured to cool the sample100to a temperature lower than or equal to the dew point in the ambient atmosphere and thereby generate condensation on the surface101of the sample100. A surface temperature sensor15is disposed on the surface101of the sample100placed on the sample stage10. On the basis of the detection result of the surface temperature sensor15, the control device90controls the sample stage10to reduce the surface temperature of the sample100to a predetermined temperature (for example, 5° C.).

In the present embodiment, the placement surface11of the sample stage10is formed as a mirror surface. Thus, when the sample100is made of a material that transmits light therethrough, such as a window glass or a lens, the object70reflected on the placement surface11is imaged via the transmission through the sample100. In this manner, even when the sample100transmits light therethrough, the object70can be imaged as with the sample100that reflects light, such as a mirror. In other words, there is no need to change the arrangement of the imaging device40, the object70, etc., depending on whether the sample100transmits light therethrough in the present embodiment. Therefore, the entire apparatus can have a simple and compact configuration.

In the present embodiment, the placement surface11is formed as a mirror surface by aluminum evaporation. However, a mirror may be disposed between the sample100and the sample stage10rather than forming the placement surface11as a mirror surface. Alternatively, the sample stage10may cool the sample100by a device other than the Peltier element12, for example, by direct cooling with the heat exchanger13.

The measuring chamber20is a thermo-hygrostat configured to house the sample100together with the sample stage10and keep the atmosphere around the sample100at a predetermined temperature and a predetermined humidity. The outer wall of the measuring chamber20has a jacket structure. A hot and cold water circulator21configured to circulate hot water or cold water at a predetermined temperature is connected to the outer wall of the measuring chamber20. A humidity regulator22configured to supply steam to regulate humidity in the measuring chamber20is connected to the measuring chamber20. An in-chamber temperature sensor23and an in-chamber humidity sensor24are disposed inside the measuring chamber20. On the basis of the detection results of the in-chamber temperature sensor23and the in-chamber humidity sensor24, the control device90controls the hot and cold water circulator21and the humidity regulator22, to keep the atmosphere in the measuring chamber20at a predetermined temperature and a predetermined humidity (for example, 20° C. and 50% RH).

An upper part of the measuring chamber20includes an observation window25made of glass having an appropriate antifog function. The imaging device40images the object70via the observation window25. Specifically, light from the object70passes through the observation window25and travels toward the sample100, and again passes through the observation window25and enters the imaging device40after being reflected at the placement surface11or the surface101of the sample100.

The antifog method in the observation window25is not limited to any particular method. For example, the glass may be heated by a heating wire heater, for example, or an antifog coating, for example, may be applied to a surface of the glass. Alternatively, the measuring chamber20may regulate its internal temperature by a device other than the hot and cold water circulator21.

The steam spray device30sprays steam to the surface101of the sample100in the measuring chamber20to forcibly generate the fogging of the surface101of the sample100. In other words, the surface101of the sample100in the present embodiment can be cooled to a temperature lower than or equal to the dew point to cause condensation naturally. Additionally, water droplets can be applied to the surface101of the sample100to forcibly generate fogging even when the surface101of the sample100has a temperature higher than the dew point. A nozzle31with its tip being directed toward the surface101of the sample100is disposed in the measuring chamber20. The steam spray device30sprays steam to the surface101of the sample100via the nozzle31.

The imaging device40images the object70via the sample100. The imaging device40is disposed at a position opposed to the surface101of the sample100with the observation window25and the half mirror50being interposed therebetween. As mentioned above, when the sample100is a window glass or a lens, the imaging device40images the object70reflected on the placement surface11behind the sample100via the transmission through the sample100. When the sample100reflects light, the imaging device40images the object70reflected on the surface101of the sample100. The imaging device40performs imaging in accordance with control made by the control device90. The imaged image is transmitted to and stored in the control device90.

The half mirror50is disposed between the imaging device40and the observation window25. The half mirror50reflects light from the object70toward the sample100and allows light reflected at the placement surface11or the surface101of the sample100to transmit therethrough to enter the imaging device40. In the present embodiment, the provision of the half mirror50increases flexibility in the arrangement of the imaging device40, the object70, and the image-adjusting lens optical system81, thereby allowing for the compact configuration of the entire apparatus.

The lighting device60illuminates the object70from behind. The lighting device60includes a light source such as a halogen lamp or an LED, for example. The lighting device60is disposed so as to project light toward the object70from a side opposite to the half mirror50. Additionally, a diffuser61configured to diffuse light is disposed in front of the lighting device60(between the lighting device60and the object70).

The object70is provided to form an appropriate figure in an image imaged by the imaging device40.FIGS. 2A to 2Dare schematic diagrams showing examples of the object70. In the present embodiment, while the details thereof will be described later, the antifog property of the sample100is evaluated on the basis of change in the object image imaged via the sample100due to the fogging of the surface101of the sample100. Thus, the object70may be any object capable of having appropriate change in pixel values (such as gray-scale levels, RGB values, or HSV values) in the object image imaged by the imaging device40.

As shown inFIGS. 2A and 2B, examples of the object70to be used may include an object in which a metal film72that transmits no light is formed on a surface of a transparent substrate71made of glass or resin, and an object in which the metal film72is interposed between two transparent substrates71. Since the object70is illuminated from behind in the present embodiment, the use of such an object70allows for the acquisition of a silhouette image with clear contrast.

In this case, the shape of the metal film72, i.e., the shape of the figure formed in the image imaged by the imaging device40is not limited to any particular shape. The shape may be circular or annular as shown inFIGS. 2A and 2B. Alternatively, the shape may have a polygonal, star, or any other shape including a variety of symbols. Furthermore, a plurality of metal films72may be formed on a single substrate71. In this case, each metal film72may have a different shape. Alternatively, an existing droplet standard sample used for the calibration of a contact angle meter may be utilized as the object70. Such a droplet standard sample allows for highly accurate evaluation of the antifog property due to the high shape accuracy of the metal film72.

Rather than forming the metal film72on the substrate71, a design, a symbol, a painting, or a picture, for example, may be printed on the substrate71as shown inFIGS. 2C and 2D, or an existing positive film, for example, may be used as the object70. In this case, the use of a gray-scaled picture or a color picture of a landscape or a person, for example, as the object70allows the evaluation of the antifog property to be performed under circumstances similar to the actual conditions.

While its diagrammatic illustration will be omitted, a flat plate, a solid, or a statue, for example, made of a material that transmits no light therethrough such as a metal or a resin, for example, may be directly used as the object70, rather than using the transparent substrate71.

Referring back toFIG. 1, the image-adjusting lens optical system81is configured to adjust the size of the object70reflected on the placement surface11or the surface101of the sample100and to adjust the amount of light incident on the imaging device40. The provision of the image-adjusting lens optical system81increases flexibility in the size and arrangement of the object70, thereby allowing for the compact and efficient configuration of the entire apparatus.

Moreover, since the object70, together with the image-adjusting lens optical system81, can be disposed so as to be appropriately spaced apart from the sample100, the sample100and the object70can be disposed separately within and outside the measuring chamber20, respectively. This can prevent the generation of condensation on a surface of the object70when generating condensation on the surface101of the sample100. Thus, influence due to the condensation generated on the surface of the object70can be eliminated.

Furthermore, the disposition of the image-adjusting lens optical system81between the object70and the sample100concentrates light from the object70, thereby preventing the image imaged by the imaging device40from being excessively darkened by the fogging of the surface101of the sample100. In other words, since there is no need to intensify light for irradiating the object70, the figure of the object70in a more natural state can be reflected on the placement surface11or the surface101of the sample100and can be imaged.

While the image-adjusting lens optical system81is constituted by two convex lenses81ain the present embodiment, the number of the convex lenses81athat constitute the image-adjusting lens optical system81is not limited thereto. Alternatively, the image-adjusting lens optical system81may be constituted by a combination of the convex lens81aand a concave lens. Alternatively, the size of the object70reflected on the placement surface11or the surface101of the sample100may be adjusted by providing a zoom mechanism in the image-adjusting lens optical system81or by providing a moving mechanism configured to move the image-adjusting lens optical system81or the object70to change their relative positions.

The surface imaging lens optical system82is configured to image the state of condensation on the surface101of the sample100by the imaging device40. As mentioned above, the antifog property evaluating apparatus1evaluates the antifog property of the sample100on the basis of images acquired by imaging the object70via the sample100. Thus, the focal length of the imaging device40basically corresponds to the position of the object70. Accordingly, in the present embodiment, the focal length is changed by inserting the surface imaging lens optical system82between the half mirror50and the imaging device40, thereby allowing both of the object70and the surface101of the sample100to be imaged by a single imaging device40.

The surface imaging lens optical system82is configured to include an appropriate convex lens82aand to be able to be retracted from an optical path by a retracting device83controlled by the control device90. More specifically, in the present embodiment, the surface imaging lens optical system82is retracted from the optical path when the object70is imaged to evaluate the antifog property. In contrast, the surface imaging lens optical system82is disposed on the optical path when the state of condensation on the surface101of the sample100is observed.

As with the image-adjusting lens optical system81, the configuration of the surface imaging lens optical system82can adopt various known configurations without being limited to any particular configuration. Alternatively, the surface imaging lens optical system82may be disposed between the measuring chamber20and the half mirror50or may be incorporated into the imaging device40. Alternatively, the retracting device83may be configured to move the surface imaging lens optical system82by hand.

The control device90is configured to control the entire antifog property evaluating apparatus1to execute evaluation on the antifog property of the sample100. The control device90is constituted by a computer including storage means such as a hard disk or a flash disk as well as a CPU, a ROM, and a RAM. The control device90is electrically connected to the components of the antifog property evaluating apparatus1. An input device (not shown) such as a keyboard and a mouse and a display device (not shown) such as a liquid crystal display are connected to the control device90. A user operates the antifog property evaluating apparatus1via such devices.

The control device90also includes control unit91and evaluation unit92as functional components implemented by the execution of programs stored, for example, in the hard disk by the CPU. The control unit91controls the sample stage10, the hot and cold water circulator21, the humidity regulator22, the steam spray device30, and the imaging device40, for example, to generate the fogging of the surface101of the sample100and executes the imaging of the object70via the sample100. The control unit91also controls the retracting device83and the imaging device40to execute the imaging of the surface101of the sample100. On the basis of the object images acquired by the control unit91, the evaluation unit92derives an antifog property evaluation index for evaluating the antifog property of the sample100by a predetermined method. An evaluation device including the evaluation unit92may be provided separately from the control device90.

The arrangement of the components of the above-described antifog property evaluating apparatus1is not limited to the one shown inFIG. 1. Different arrangements may be adopted. For example, the sample100may be disposed with the surface101facing a lateral side, and imaging may be performed by the imaging device40disposed on the lateral side. Alternatively, the sample100may be disposed with the surface101facing downward or in an oblique direction. The surface101of the sample100facing, for example, the lateral side allows for the evaluation of the antifog property while taking gravitational influence on condensation into account.

A procedure of evaluating an antifog property by the antifog property evaluating apparatus1will be described next. In the evaluation of the antifog property, the sample100is first placed on the placement surface11of the sample stage10. The sample100may be placed by hand or automatically by an appropriate conveyer, for example. Next, the control unit91of the control device90controls the hot and cold water circulator21and the humidity regulator22to keep the atmosphere in the measuring chamber20at a preset temperature and a preset humidity (atmosphere setting step).

If it is confirmed that the inside of the measuring chamber20is being kept at the preset temperature and humidity on the basis of the detection results of the in-chamber temperature sensor23and the in-chamber humidity sensor24, the control unit91controls the lighting device60and the imaging device40to image the object70via the sample100in order to acquire an object image when no fogging is present on the surface101of the sample100(imaging step before the generation of fogging). The acquired object image is stored in the storage means included in the control device90and displayed on the display device.

Next, the control unit91controls the sample stage10to cool the sample100to a temperature lower than or equal to the dew point in order to generate the fogging of the surface101(fogging generation step). At the same time, the control unit91also controls the imaging device40to image the object70via the sample100(imaging step after the generation of fogging). In the imaging step after the generation of fogging, the control unit91acquires an object image when fogging is present on the surface101of the sample100at predetermined intervals (for example, every second) in order to record time-varying change of the fogging. The acquired object images are stored in the storage means included in the control device90and displayed on the display device.

When fogging is generated on the surface101of the sample100by the steam spray device30, the control unit91controls the steam spray device30to spray steam to the surface of the sample100in the fogging generation step. In this case, steam may be sprayed after the surface101of the sample100is cooled to a predetermined temperature by the sample stage10.

Once the object images are stored in the storage means, the evaluation unit92of the control device90next derives the antifog property evaluation index on the basis of the stored object images (evaluation step). The derived antifog property evaluation index is stored in the storage means and displayed on the display device. The evaluation on the antifog property of the sample100is completed through the above procedure.

In the imaging step before the generation of fogging and the imaging step after the generation of fogging, the surface101of the sample100may be imaged together with the imaging of the object70via the sample100. In this case, the control unit91controls the retracting device83and the imaging device40at appropriate timing before and after the imaging of the object70to image the surface101of the sample100to acquire surface images. Intervals to acquire such surface images in the imaging step after the generation of fogging may be the same as, or different from, the intervals to acquire the object images. The observation of the condensation state on the surface101along with the evaluation of the antifog property allows for more multilateral evaluation.

Alternatively, only the imaging of the surface101of the sample100may be performed in the imaging step before the generation of fogging and the imaging step after the generation of fogging by performing the above-described procedure with the surface imaging lens optical system82being disposed in advance on the optical path. In this case, change in the state of the surface101of the sample100can be observed in detail, although the antifog property evaluation index cannot be derived.

A method for deriving the antifog property evaluation index will be described next in detail.FIG. 3Ais a schematic diagram showing one example of an object image200acquired when no fogging is present on the surface101of the sample100.FIG. 3Bis a schematic diagram showing one example of an object image201acquired when fogging is present on the surface101of the sample100. These figures schematically show examples when the object70shown inFIG. 2Ais imaged.

The image acquired by imaging the object70is a silhouette image as mentioned above. Specifically, the metal film72of the object70transmits no light from the lighting device60, and thus the metal film72is shown as a dark region200aor201athat is darker than its surrounding region. The transparent substrate71is shown as a light region200bor201bthat is lighter than the dark region200aor201a. When no fogging (condensation) is present on the surface101of the sample100, there is no scattering of light due to fogging. Therefore, even when the object70is imaged via the sample100, the shape of the metal film72in the object70is clearly shown as illustrated inFIG. 3A, resulting in the object image200with a substantially clear boundary (edge) between the dark region200aand the light region200b.

When fogging (condensation) is present on the surface101of the sample100, on the other hand, light scatters due to the fogging. Therefore, the shape of the metal film72in the object70is shown in a blurred manner as illustrated inFIG. 3B, resulting in the object image201with an unclear boundary (edge) between the dark region201aand the light region201b. Moreover, the light region201bin the object image201has reduced overall brightness as compared to the light region200bin the object image200due to the scattering of light.

In other words, the object image201acquired when fogging is present on the surface101of the sample100is different from the object image200acquired when no fogging is present on the surface101of the sample100. More specifically, pixel values (such as gray-scale levels, RGB values, or HSV values) of at least part of pixels in the object image201are different from the pixel values of the pixels at the same positions in the object image200as a result of the scattering of light due to fogging.

In the present embodiment, the antifog property of the sample100can be evaluated quantitatively and objectively by deriving the antifog property evaluation index that quantifies the degree of such change in the object image201from the object image200. Moreover, the degree of change in the object image201from the object image200represents the degree of change in the visibility of sight via the sample100(transmitted or reflected). Thus, the antifog property can be directly evaluated in a more realistic situation.

The method for deriving the antifog property evaluation index can adopt various methods utilizing various known image processing methods and image analysis methods without being limited to any particular method. Note however that the antifog property evaluation index is derived in the present embodiment by any one of six methods to be described below: an area ratio method; a slope ratio method; a contrast ratio method; a distance ratio method; a compression ratio method; and a histogram method. In the following, each of these methods will be described taking, as an example, a case where the object images200and201shown inFIGS. 3A and 3Bare acquired as gray-scaled images with 256 levels of gray.

FIGS. 4A and 4Bare schematic diagrams showing a general concept of the area ratio method. In the area ratio method, the antifog property evaluation index is derived on the basis of areas S0and S1of regions A0and A1where pixel values P of pixels in the regions are smaller than or equal to a predetermined threshold Pta in the object images200and201before and after the generation of fogging. Specifically, the evaluation unit92of the control device90first derives the area S0of the region A0where the pixel values P (here, gray-scale levels) of the pixels in this region are smaller than or equal to the predetermined threshold Pta in the object image200acquired when no fogging is present on the sample100as shown inFIG. 4A.

Next, the evaluation unit92derives the area S1of the region A1where the pixel values P of the pixels are smaller than or equal to the predetermined threshold Pta in the object image201acquired when fogging is present on the sample100as shown inFIG. 4B. The evaluation unit92then derives a ratio S1/S0or S0/S1between the area S1and the area S0as the antifog property evaluation index.

The area S1becomes smaller than the area S0as the degree of light scattering due to the fogging of the sample100increases, because the dark region201ais illuminated to brighten it up (i.e., to raise the level of gray). When there is almost no light scattering due to fogging, on the other hand, the area S1has a value close to the area S0. Therefore, when the ratio S1/S0is derived as the antifog property evaluation index, the antifog property of the sample100becomes higher as the value of the antifog property evaluation index becomes larger (closer to 1), and the antifog property of the sample100becomes lower as the value of the antifog property evaluation index becomes smaller. When the ratio S0/S1is derived as the antifog property evaluation index, the opposite applies.

Note that the value of the area S1may be directly used as the antifog property evaluation index rather than obtaining the area ratio S1/S0or S0/S1. When the object images200and201are acquired as color images, the median value, average value, or weighted average value, for example, of an R (red) value, a G (green) value, and a B (blue) value or an H (hue) value, an S (saturation) value, and a V (value) value may be used as the pixel value P. Alternatively, any one of the R value, the G value, and the B value, or any one of the H value, the S value, and the V value may be used as the pixel value P.

Alternatively, the antifog property evaluation index may be derived on the basis of areas of regions where the pixel values P of their pixels are larger than or equal to the predetermined threshold Pta. In this case, as the degree of light scattering increases, the light region201bbecomes darker. Therefore, the area of the region where the pixel values P of its pixels are larger than or equal to the predetermined threshold Pta becomes smaller accordingly. Alternatively, the object images200and201may be transformed into binary images on the basis of the predetermined threshold Pta and the obtained images may be displayed on the display device, for example. This can visually show change in the areas of the regions A0and A1or change in their shapes.

FIGS. 5A and 5Bare schematic diagrams showing a general concept of the slope ratio method. In the slope ratio method, the antifog property evaluation index is derived on the basis of a rate of change in the pixel values P of pixels on a route R set in the object images200and201before and after the generation of fogging. Specifically, the evaluation unit92of the control device90first sets the route R in a horizontal direction (x direction) extending over the dark region200aand the light region200bin the object image200acquired when no fogging is present on the sample100as shown inFIG. 5A. The evaluation unit92then obtains the pixel values P of pixels on the route R to derive an average slope angle θ0as a rate of change in the pixel value P at a boundary B.

Next, the evaluation unit92sets the same route R as the object image200in the object image201acquired when fogging is present on the sample100as shown inFIG. 5B. The evaluation unit92obtains the pixel values P of pixels on the route R to derive an average slope angle θ1as a rate of change in the pixel value Pin the boundary B. The evaluation unit92then derives a ratio θ1/θ0or θ0/θ1between the average slope angle θ1and the average slope angle θ0as the antifog property evaluation index.

In this example, since the object image200has high contrast, the pixel value P on the route R in the object image200suddenly changes at the boundary B from a substantially constant state at the maximum value (255) to a substantially constant state at an approximately minimum value (0). Thus, the average slope angle θ0is approximately 90°. On the route R in the object image201, on the other hand, as the degree of light scattering due to the fogging of the sample100increases, the light region201bbecomes darker and a width W of the boundary B increases. Since the pixel value P gradually changes within such a width W, the average slope angle θ1becomes smaller accordingly. When there is almost no light scattering due to fogging, the average slope angle θ1has a value close to the average slope angle θ0.

Therefore, when the ratio θ1/θ0is derived as the antifog property evaluation index, the antifog property of the sample100becomes higher as the value of the antifog property evaluation index becomes larger (closer to 1), and the antifog property of the sample100becomes lower as the value of the antifog property evaluation index becomes smaller. When the ratio θ0/θ1is derived as the antifog property evaluation index, the opposite applies.

As with the case of the area ratio method, the value of the average slope angle θ1may be directly used as the antifog property evaluation index. When the object images200and201are acquired as color images, the median value, average value, or weighted average value, for example, of the R value, the G value, and the B value or the H value, the S value, and the V value may be used as the pixel value P. Alternatively, any one of the R value, the G value, and the B value, or any one of the H value, the S value, and the V value may be used as the pixel value P.

Without being limited to any particular position, the position of the route R can be set anywhere as long as the route R crosses the boundary B where the pixel value P changes. Also, the direction of the route R may be any direction without being limited to the x direction. For the pixel values P to be obtained, only the pixel values P of the pixels on the route R may be obtained, or the average value, for example, of the pixel values P of a pixel on the route R and its adjacent pixel may be obtained. Alternatively, a plurality of routes R may be set, and the antifog property evaluation index may be derived on the basis of the average value of the average slope angles θ0in the routes R and the average value of the average slope angles θ1in the routes R.

FIGS. 6A and 6Bare schematic diagrams showing a general concept of the contrast ratio method. In the contrast ratio method, the antifog property evaluation index is derived on the basis of differences ΔP0and ΔP1between pixel values P at a first comparison point La and a second comparison point Lb set in the object images200and201before and after the generation of fogging. Specifically, the evaluation unit92of the control device90first sets the first comparison point La in the dark region200aand sets the second comparison point Lb in the light region200bin the object image200acquired when no fogging is present on the sample100as shown inFIG. 6A. Thereafter, the evaluation unit92obtains a pixel value Pa0at the first comparison point La and a pixel value Pb0at the second comparison point Lb. The evaluation unit92then derives the difference ΔP0(=Pb0−Pa0) therebetween.

Next, in the object image201acquired when fogging is present on the sample100, the evaluation unit92sets the first comparison point La and the second comparison point Lb at the same positions as the object image200as shown inFIG. 6B. Thereafter, the evaluation unit92obtains a pixel value Pa1at the first comparison point La and a pixel value Pb1at the second comparison point Lb. The evaluation unit92then derives the difference ΔP1(=Pb1−Pa1) therebetween. The evaluation unit92then derives a ratio ΔP1/ΔP0or ΔP0/ΔP1between the difference ΔP1and the difference ΔP0as the antifog property evaluation index.

In this example, since the object image200has high contrast as mentioned above, the pixel value Pa0at the first comparison point La has an approximately minimum value (0) and the pixel value Pb0at the second comparison point Lb has an approximately maximum value (255) in the object image200. Therefore, the difference ΔP0has an approximately maximum value (255). In the object image201, on the other hand, as the degree of light scattering due to the fogging of the sample100increases, the light region201bbecomes darker and thus the pixel value Pb1at the second comparison point Lb decreases. In the object image201, as the degree of light scattering due to the fogging of the sample100increases, the dark region201abecomes lighter and thus the pixel value Pa1at the first comparison point La increases. Therefore, the difference ΔP1becomes much smaller accordingly. This fact is very unique discovery. Therefore, the difference ΔP1becomes smaller accordingly. When there is almost no light scattering due to fogging, the difference ΔP1has a value close to the difference ΔP0.

Therefore, when the ratio ΔP1/ΔP0is derived as the antifog property evaluation index, the antifog property of the sample100becomes higher as the value of the antifog property evaluation index becomes larger (closer to 1), and the antifog property of the sample100becomes lower as the value of the antifog property evaluation index becomes smaller. When the ratio ΔP0/ΔP1is derived as the antifog property evaluation index, the opposite applies.

As with the cases of the above-described methods, the value of the difference ΔP1may be directly used as the antifog property evaluation index. When the object images200and201are acquired as color images, the median value, average value, or weighted average value, for example, of the R value, the G value, and the B value or the H value, the S value, and the V value may be used as the pixel value P. Alternatively, any one of the R value, the G value, and the B value, or any one of the H value, the S value, and the V value may be used as the pixel value P.

Without being limited to any particular positions, the first comparison point La and the second comparison point Lb can be set at appropriate positions in accordance with, for example, the configuration of the object70. For the pixel values P to be obtained, only the pixel values P of the pixels at the first comparison point La and the second comparison point Lb may be obtained, or the average values, for example, of the pixel values P of the pixels at the first comparison point La and the second comparison point Lb and their adjacent pixels may be obtained. Alternatively, a pixel having the minimum pixel value P may be used as the first comparison point La and a pixel having the maximum pixel value P may be used as the second comparison point Lb in the entire image or on a predetermined route in the image, for example, rather than fixing the positions of the first comparison point La and the second comparison point Lb.

Alternatively, a plurality of first comparison points La and a plurality of second comparison points Lb may beset, and the anti fog property evaluation index may be derived on the basis of the average value of the plurality of differences ΔP0and the average value of the plurality of differences ΔP1. Alternatively, the antifog property evaluation index may be derived on the basis of not the differences ΔP0and ΔP1but a ratio Pb0/Pa0or Pa0/Pb0between the pixel value Pa0and the pixel value Pb0and a ratio Pb1/Pa1or Pa1/Pb1between the pixel value Pa1and the pixel value Pb1.

FIGS. 7A and 7Bare schematic diagrams showing a general concept of the distance ratio method. In the distance ratio method, the antifog property evaluation index is derived on the basis of distances D0and D1from a starting point Ls to goal points Lg0and Lg1at which the pixel value P becomes larger than or equal to a predetermined threshold Ptd for the first time on a route R set in the object images200and201before and after the generation of fogging. Specifically, the evaluation unit92of the control device90first sets the starting point Ls in the dark region200ain the object image200acquired when no fogging is present on the sample100as shown inFIG. 7A. The evaluation unit92then sets the route R in a horizontal direction (x direction) from the starting point Ls. Thereafter, the evaluation unit92obtains, sequentially from the starting point Ls, the pixel values P of the pixels on the route R. The evaluation unit92sets, as the goal point Lg0, a point (pixel) at which the pixel value P becomes larger than or equal to the predetermined threshold Ptd for the first time. Thereafter, the evaluation unit92derives the distance D0from the starting point Ls to the goal point Lg0.

Next, in the object image201acquired when fogging is present on the sample100, the evaluation unit92sets the starting point Ls at the same position as the object image200and sets the same route R as the object image200as shown inFIG. 7B. Thereafter, the evaluation unit92obtains, sequentially from the starting point Ls, the pixel values P of the pixels on the route R. The evaluation unit92sets, as the goal point Lg1, a point at which the pixel value P becomes larger than or equal to the predetermined threshold Ptd for the first time. The evaluation unit92then derives the distance D1from the starting point Ls to the goal point Lg1. Finally, the evaluation unit92derives a ratio D1/D0or D0/D1between the distance D0and the distance D1as the antifog property evaluation index.

As the degree of light scattering due to the fogging of the sample100increases, an area around the dark region201abecomes darker (i.e., the level of gray is lowered). Therefore, the distance D1becomes larger than the distance D0accordingly. When there is almost no light scattering due to fogging, on the other hand, the distance D1has a value close to the distance D0. Therefore, when the ratio D1/D0is derived as the antifog property evaluation index, the antifog property of the sample100becomes higher as the value of the antifog property evaluation index becomes smaller (closer to 1), and the antifog property of the sample100becomes lower as the value of the antifog property evaluation index becomes larger. When the ratio D0/D1is derived as the antifog property evaluation index, the opposite applies.

As with the cases of the above-described methods, the value of the distance D1may be directly used as the antifog property evaluation index. When the object images200and201are acquired as color images, the median value, average value, or weighted average value, for example, of the R value, the G value, and the B value or the H value, the S value, and the V value may be used as the pixel value P. Alternatively, any one of the R value, the G value, and the B value, or any one of the H value, the S value, and the V value may be used as the pixel value P.

Without being limited to any particular position, the starting point Ls can be set at an appropriate position in accordance with, for example, the configuration of the object70. Also, the direction of the route R may be any direction without being limited to the x direction. For the pixel values P to be obtained, only the pixel values P of the pixels on the route R may be obtained, or the average value, for example, of the pixel values P of a pixel on the route R and its adjacent pixel may be obtained. Alternatively, a plurality of starting points Ls or a plurality of routes R may be set, and the antifog property evaluation index may be derived on the basis of the average value of the plurality of distances D0and the average value of the plurality of distances D1.

FIGS. 8A and 8Bare schematic diagrams showing a general concept of the compression ratio method. In the compression ratio method, the antifog property evaluation index is derived on the basis of compress ion ratios Cr0and Cr1when uncompressed object images2000and201obefore and after the generation of fogging are compressed by a predetermined image compression method. Specifically, the evaluation unit92of the control device90first compresses the uncompressed (for example, a RAW format or a BMP format) object image2000acquired when no fogging is present on the sample100by the predetermined image compression method to generate the object image200in a JPEG format, for example, as shown inFIG. 8A. The evaluation unit92then obtains a file capacity C0oof the object image2000and a file capacity C0of the object image200to derive a compression ratio Cr0(=C0/C0o).

Next, the evaluation unit92compresses the uncompressed object image201oacquired when fogging is present on the sample100by the same image compression method as with the object image2000to generate the object image201in the same format as the object image200as shown inFIG. 8B. The evaluation unit92then obtains a file capacity C1oof the object image201oand a file capacity C1of the object image201to derive a compression ratio Cr1(=C1/C1o). Finally, the evaluation unit92derives a ratio Cr1/Cr0or Cr0/Cr1between the compression ratio Cr1and the compression ratio Cr0as the antifog property evaluation index.

In this example, since the object image has high contrast as mentioned above, the object image200is similar to a substantially binary image. Thus, the compression ratio Cr0has a high value. In the object image201, on the other hand, as the degree of light scattering due to the fogging of the sample100increases, the degree of change in the level of gray, i.e., the pixel value P increases. Thus, the compression ratio Cr1has a lower value accordingly. When there is almost no light scattering due to fogging, the compression ratio Cr1has a value close to the compression ratio Cr0.

Therefore, when the ratio Cr1/Cr0is derived as the antifog property evaluation index, the antifog property of the sample100becomes higher as the value of the antifog property evaluation index becomes larger (closer to 1), and the antifog property of the sample100becomes lower as the value of the antifog property evaluation index becomes smaller. When the ratio Cr0/Cr1is derived as the antifog property evaluation index, the opposite applies.

Note that the antifog property evaluation index may be derived using not the compression ratios Cr0and Cr1but the compressed file capacities C0and C1. Alternatively, the value of the compression ratio Cr1or the values of the compressed file capacities C0and C1may be directly used as the antifog property evaluation index as with the cases of the above-described methods. Moreover, the image format of the uncompressed object images2000and201oand the image format of the compressed object images200and201may adopt various known image formats without being limited to any particular image format. Also, the image compression method is not limited to any particular method. For example, the antifog property evaluation index may be derived on the basis of the compression ratios Cr0and Cr1when the object images200oand201oare compressed in a ZIP format.

If the object70having a complicated configuration as shown inFIGS. 2C and 2Dis used, for example, the degree of change in the pixel value P may decrease as the degree of light scattering due to fogging increases. As a result, the compression ratio Cr1may be lower than the compression ratio Cr0. Therefore, it is preferred in the compression ratio method to check the relationship between the value of the antifog property evaluation index and the antifog property beforehand depending on the object70to be used.

FIGS. 9A and 9Bare schematic diagrams showing a general concept of the histogram method. In the histogram method, the antifog property evaluation index is derived based on histogram areas Sh0and Sh1of pixel values P in the object images200and201before and after the generation of fogging. Specifically, the evaluation unit92of the control device90first generates a histogram, wherein the longitudinal axis thereof represents appearance frequency F and the horizontal axis thereof represents the pixel value P, about the object image200acquired when no fogging is present on the sample100as shown inFIG. 9A. The evaluation unit92then derives the area Sh0of the generated histogram.

Next, the evaluation unit92generates, as with the object image200, a histogram, wherein the longitudinal axis thereof represents the appearance frequency F and the horizontal axis thereof represents the pixel value P, about the object image201acquired when fogging is present on the sample100as shown inFIG. 9B. The evaluation unit92then derives the area Sh1of the generated histogram. Thereafter, the evaluation unit92derives a ratio Sh1/Sh0or Sh0/Sh1between the area Sh1and the area Sh0as the antifog property evaluation index.

In this example, since the object image200has high contrast as mentioned above, the appearance frequencies F of the pixel values P in the object image200are concentrated around values in the vicinity of the minimum value (0) and the maximum value (255), resulting in the small histogram area Sh0. In the object image201, on the other hand, as the degree of light scattering due to the fogging of the sample100increases, the appearance frequencies F of the intermediate pixel values P increase, resulting in the large histogram area Sh1. When there is almost no light scattering due to fogging, on the other hand, the area Sh1has a value close to the area Sh0.

Therefore, when the ratio Sh1/Sh0is derived as the antifog property evaluation index, the antifog property of the sample100becomes higher as the value of the antifog property evaluation index becomes smaller (closer to 1), and the antifog property of the sample100becomes lower as the value of the antifog property evaluation index becomes larger inversely with the above-described methods. When the ratio Sh0/Sh1is derived as the antifog property evaluation index, the opposite applies.

As with the cases of the above-described methods, the value of the area Sh1may be directly used as the antifog property evaluation index. When the object images200and201are acquired as color images, the median value, average value, or weighted average value, for example, of the R value, the G value, and the B value or the H value, the S value, and the V value may be used as the pixel value P. Alternatively, any one of the R value, the G value, and the B value, or any one of the H value, the S value, and the V value may be used as the pixel value P. When the object70having a complicated configuration as shown inFIG. 2Dis used, in particular, a more appropriate antifog property evaluation index may be derived by limiting the histogram to any one of the R value, the G value, and the B value, or any one of the H value, the S value, and the V value.

The evaluation unit92of the control device90derives the antifog property evaluation index using any one of the above-described methods. A user may select which one of these methods to use by hand, or the evaluation unit92may determine which one of the methods to use in accordance with, for example, the type of the object70or the configuration of the acquired object image200.

As described above, the antifog property evaluating apparatus1according to the present embodiment includes: the fogging generation device (the sample stage10and the steam spray device30) configured to generate the fogging of the surface101of the sample100; the object70disposed at a position different from that of the sample100; the imaging device40configured to image the object70via the sample100; and the evaluation device (the evaluation unit92of the control device90) configured to evaluate the antifog property of the sample100on the basis of the object images200and201acquired by imaging the object70.

Such a configuration allows for the imaging of the object70via the sample100under circumstances similar to the actual use conditions of the sample100such as when an outside view is seen through a car window or when a face reflected on a mirror is seen, for example, and allows for evaluation on the antifog property of the sample100on the basis of the resultant object images200and201. Thus, the antifog property can be evaluated quantitatively and objectively in a more realistic situation.

The antifog property evaluating apparatus1also includes the image-adjusting lens optical system81disposed between the sample100and the object70. This allows an image of the object70with an appropriate size to be imaged in a more natural state.

The antifog property evaluating apparatus1also includes the lighting device60configured to illuminate the object70from behind. This allows for the acquisition of the high-contrast object images200and201, and thus the evaluation of the antifog property based on the object images200and201can be performed with high accuracy.

The antifog property evaluating apparatus1also includes the surface imaging lens optical system82to be disposed between the sample100and the imaging device40and the retracting device83configured to retract the surface imaging lens optical system82from the optical path. This allows for the imaging of the state of the surface101of the sample100by the imaging device40. Thus, the antifog property can be evaluated in a more multilateral way.

The evaluation device (the evaluation unit92of the control device90) derives the anti fog property evaluation index of the sample100on the basis of change in the object image201acquired when fogging is generated on the surface of the sample100by the fogging generation device (the sample stage10and the steam spray device30). This allows for the evaluation of the antifog property based on the degree of change in the visibility of sight via the sample100. Thus, the antifog property can be directly evaluated in a more realistic situation.

The evaluation device (the evaluation unit92of the control device90) derives the antifog property evaluation index on the basis of the areas S0and S1of the regions A0and A1where the pixel values P are smaller than or equal to, or larger than or equal to, the predetermined threshold Pta in the object images200and201. Thus, the quantitative and objective evaluation of the antifog property based on the antifog property evaluation index can be performed in a simple and highly accurate manner.

The evaluation device (the evaluation unit92of the control device90) derives the antifog property evaluation index on the basis of the rates of change (the average slope angles θ0and θ1) in the pixel values P on the route R set in the object images200and201. The quantitative and objective evaluation of the antifog property based on the antifog property evaluation index can be performed in a simple and highly accurate manner also in this case.

The evaluation device (the evaluation unit92of the control device90) derives the antifog property evaluation index on basis of the differences ΔP0and ΔP1or ratios between the pixel values P at the first comparison point La and the second comparison point Lb set in the object images200and201. The quantitative and objective evaluation of the antifog property based on the antifog property evaluation index can be performed in a simple and highly accurate manner also in this case.

The evaluation device (the evaluation unit92of the control device90) derives the antifog property evaluation index on the basis of the distances D0and D1from the starting point Ls to the goal points Lg0and Lg1at which the pixel value P becomes larger than or equal to the predetermined threshold Ptd for the first time on the route R set in the object images200and201. The quantitative and objective evaluation of the antifog property based on the antifog property evaluation index can be performed in a simple and highly accurate manner also in this case.

The evaluation device (the evaluation unit92of the control device90) derives the antifog property evaluation index on the basis of the compression ratios Cr0and Cr1when the uncompressed object images2000and201oare compressed by a predetermined image compression method or the compressed file capacities C0and C1. The quantitative and objective evaluation of the antifog property based on the antifog property evaluation index can be performed in a simple and highly accurate manner also in this case.

The evaluation device (the evaluation unit92of the control device90) derives the antifog property evaluation index on the basis of the histogram areas Sh0and Sh1of the pixel values P in the object images200and201. The quantitative and objective evaluation of the antifog property based on the antifog property evaluation index can be performed in a simple and highly accurate manner also in this case.

The antifog property evaluating method according to the present embodiment includes: the fogging generation step of generating the fogging of the surface of the sample100; the imaging step of imaging the object70disposed at the position different from that of the sample100via the sample100; and the evaluation step of evaluating the antifog property of the sample100on the basis of the object images200and201acquired by imaging the object70.

Such a configuration allows for the imaging of the object70via the sample100under circumstances similar to the actual use conditions of the sample100and allows for evaluation on the antifog property of the sample100based on the resultant object images200and201. Thus, the antifog property can be evaluated quantitatively and objectively in a more realistic situation.

In the evaluation step, the antifog property evaluation index of the sample100is derived on the basis of change in the object images200and201when fogging is generated on the surface of the sample100in the fogging generation step. This allows for the evaluation of the antifog property based on the degree of change in the visibility of sight via the sample100. Thus, the antifog property can be directly evaluated in a more realistic situation.

While the embodiments of the present invention have been described above, it is to be understood that the antifog property evaluating apparatus and the antifog property evaluating method according to the present invention are not limited to the above-described embodiments and various modifications thereof may be made without departing from the scope of the present invention. Moreover, the functions and effects described in the aforementioned embodiments are merely the recitation of the most preferred functions and effects that can be obtained by the present invention. Functions and effects of the present invention are not limited thereto.

The antifog property evaluating apparatus and the antifog property evaluating method according to the present invention can be utilized for evaluation on the antifog properties of various materials that transmit or reflect light or evaluation on the antifog properties of coating agents to be applied onto the surfaces of various materials.

The entire disclosure of Japanese Patent Application No. 2015-216697 filed Nov. 4, 2015 including specification, claims, drawings, and summary are incorporated herein by reference in its entirety.