WO2022067047A1

WO2022067047A1 - System and method for evaluation of optical defects of a glazing

Info

Publication number: WO2022067047A1
Application number: PCT/US2021/051968
Authority: WO
Inventors: Markus Walter POHLEN; Norihiro Kato
Original assignee: Carlex Glass America, Llc
Priority date: 2020-09-25
Filing date: 2021-09-24
Publication date: 2022-03-31

Abstract

A method of evaluating a glazing. The method comprises: projecting a test pattern on a specimen glazing; capturing an image of the test pattern reflected by the specimen glazing; determining or obtaining a pixel range of the image; moving the pixel range across the image for calculating a contrast of each set of pixels included in the pixel range; generating a local contrast image based on all calculated contrasts; and identifying defects in the specimen glazing based at least on the local contrast image.

Description

SYSTEM AND METHOD FOR EVALUATION OF OPTIC AL DE FECTS OF A GLAZI NG

Cross Reference to Related Application

[0001] This application claims priority to U.S. Provisional Patent Application No. 63/083,155 filed on September 25, 2020, entitled “SYSTEM AND METHOD FOR EVALUATION OF OPTICAL DEFECTS OF A GLAZING,” the content of which is incorporated by reference herein in its entirety.

Field of Technology

[0002] Th e present disclosure generally relates to a system and method for evaluating optical defects in a laminated glazing, and more particularly relates to a system, method, and non- transitory computer-readable medium for evaluating defects or surface irregularities, such as orange peel in a vehicle laminated glazing which may be used with, e.g., head-up display (HUD) systems, heatable, or infrared-ray reflecting (IRR) functions, etc.

Background

[0003] A laminated vehicle glazing, such as a windshield, may include a functional layer. In one example, a function layer may be used with a HUD system.

[0004] Automotive HUD systems generally include a projector that projects light onto a windshield of vehicle. This light is then reflected into the driver’s eyes and appears as a virtual image on the windshield at a comfortable viewing distance from the driver. In conventional HU D systems, the image source of the HUD projector may emit multiple rays of non-polarized or s- polarized light at different angles from a common origin. The non-polarized or s-polarized light that is reflected into the driver’s eyes from the inner and outer air interfaces of the windshield creates the virtual image and a ghost image, respectively, and results in a double image. The windshield generally comprises laminated safety glass made from two layers of glass that are bonded together with one or more layers of polyvinyl butyral (PVB). Most windshields are not simple flat structures but include slight curvatures in both the horizontal and vertical dimensions. The ghosting problem is illustrated in Fig. 1 for standard windshields 110 that have no wedge angle. The solid lines show the paths of light from an image source 102 (e.g, from a HUD projector), reflecting off the inner and outer windshield-air interlaces, respectively, into the driver's eye 108 to form the virtual image 104 and ghost image 106. The virtual and ghost images 104 and 106 do not entirely align to the driver’s eye 108; therefore, the overall image is blurred for the driver.

[0005] To eliminate this ghosting effect, the angular separation between the virtual and ghost images must be less than the angular resolution of the human eye, which is typically in a range about 0.1 to 0.5 mrad. A PVB interlayer with a small wedge angle is normally used to eliminate the ghost image for a driver at a defined location. The optimum wedge angle may be dependent on the location of the driver’s eyes, as well as the mounting angle, thickness, and curvature of the windshield. This use of a PVB interlayer with a smal l wedge angle may cause the virtual and ghost images to overlap to some extent, resulting in a sharper image. However, a wedge-shaped PVB interlayer is not adjustable and the images may be aligned only for drivers at a particular height. Moreover, adding a wedge to a windshield can increase cost and manufacturing complexity, and achievable wedge angles for practical devices are very limited.

[0006] One possible solution is to use a HUD projector which may emit P-polarized light and a functional layer which may reflect P-polarized light, rotate a polarization orientation from P- polarization to S-polarization, such as with a halfwave retarder film, or be a holographic film. The functional layer may be laminated into a windshield in an autoclaving process. However, such a functional layer may cause unacceptable defects such as wrinkles, orange peel, dimples/dents showing a strong local dot-like contrast, or other defects including an unacceptable film manufacturing direction, after the lamination. Even a small deviation in the HUD functional layer may result in a large and unacceptable HUD image deformation or blurriness,

[0007] In another example, a functional layer may provide infrared-ray reflection (1RR) which may be heatable to improve comfort for a driver or passenger of a vehicle. Where the functional layer is laminated into a vehicle glazing, such a functional layer may also face the problem of defects, such as wrinkles, orange peel, dimplcs'dents, or any other defects including unacceptable film manufacturing direction, after a lamination process. Such defects presented in the IRR functional layer may results in an unacceptable appearance of the glazing and may provide an undesirable reflective color shift or decrease in IRR function in an area around the defects.

[0008] Accordingly, there is a need to accurately evaluate the aforementioned defects such as wrinkles or orange peel which may be presented in a functional layer laminated into a windshield. Summary

[0009] Among other features, the present disclosure provides a method of evaluating a glazing, comprising: projecting a test pattern on a specimen glazing; capturing an image of the test pattern reflected by the specimen gl azing; determ ining or obtaining, by a processor of a computing device, a pixel range of the image; continuously moving the pixel range across the image for calculating a contrast of each set of pixels included in the pixel range; generating a local contrast image based on all calculated contrasts; identifying defects in the specimen glazing based at least on the local contrast image.

[0010] In one embodiment, the specimen glazing may comprise a first glass substrate, a second glass substrate, a first polymer interlayer between the first and second glass substrates, and a functional layer between the first and second glass substrates. The functional layer may have a reflectivity of at least 1% for a visible light wavelength. The functional film may include a polymer base film and a functional coating. The polymer base film may be made of polyethylene terephthalate or cellulose triacetate (TAC). The image may be captured by a camera, and the functional coating may be positioned between the camera and the polymer base film. Further, the polymer base film may have an index of refraction substantially the same as at least one of the first and second glass substrates, hi certain embodiments, the functional layer may be part of a head- up display system. The functional layer may reflect P-polarized light. The functional layer may include an infrared reflective layer. In addition, the functional layer may include a polarization rotator. The functional layer may include a liquid crystal layer. The functional layer may include a holographic layer. In another embodiment, the functional layer may include a functional coating. The specimen glazing may further comprise a second interlayer between the functional layer and the second glass substrate, wherein the second interlayer has a thickness of 0.1 mm or less. The image may be projected with P-polarized light, or projected with circular polarized light. The image may be projected at an angle within 10 degrees of the Brewster’s angle of at least one of the first glass substrate and the second glass substrate.

[0011] Additionally, the method may comprise setting a threshold local contrast value for identification of a defect; identifying the defects in the specimen glazing based at least on the threshold local contrast; calculating an average local contrast over a portion of the image of the specimen glazing; and evaluating the local contrast image to determine orange peel effects caused by the functional film. In one embodiment, the line pattern may include parallel lines, and the parallel lines may be vertically oriented in relation to the specimen glazing, hi another embodiment, the parallel lines may be horizontally oriented in relation to the specimen glazing. Moreover, the image may be more based on a reflection of the functional layer than ano ther surface. Determining the pixel range of the image may be performed by a processor of a computing device, in accordance with aspects of the present disclosure, hi certain embodiments, the local contrast image may include a color scale image.

[0012] The present disclosure further provides a method of evaluating a glazing. The method may comprise projecting a test pattern on a specimen glazing; capturing an image of the test pattern reflected by the specimen glazing; determining or obtaining a pixel range of the image; moving the pixel range across the image for calculating a contrast of each set of pixels included in the pixel range; generating a local contrast image based on all calculated contrasts; converting the local contrast image into a color scale image; and identifying defects in the specimen glazing based at least on the color scale image.

[0013] T he present disclosure also provides a system for evaluating a glazing. In one embodiment, the system comprises a display configured to project a test pattern on a specimen glazing and an image capturing device configured to capture an image of the test pattern reflected by the specimen glazing. The system also comprises a computing device including a processor configured to: determine a pixel range of the image or obtain a pre-determined pixel range of the image; continuously move the pixel range across the image for calculating a contrast of each set of pixels included in the pixel range; generate a local contrast image based on all calculated contrasts; and identify defects in the specimen glazing based at least on the local contrast image.

[0014] In addition, the present disclosure provides a non-transitory computer-readable medium comprising code that, when executed by a processor of a computing device, causes the processor to perform: obtaining an image of a test pattern projected on and reflected by a specimen glazing; determining a pixel range of the image or obtaining a pre-determined pixel range of the image; continuously moving tire pixel range across the image for calculating a contrast of each set of pixels included in the pixel range; generating a local contrast image based on all calculated contrasts; and identifying defects in the specimen glazing based at least on the local contrast image.

[0015] T he above simplified summary of example aspects serves to provide a basic understanding of the present disclosure. This summary is not an extensive overview of all contemplated aspects and is intended to nei ther identify key or critical elements of all aspects nor delineate the scope of any or all aspects of the present disclosure. Its sole purpose is to present one or more aspects in a simplified form as a prelude to the more detailed description o f the disclosure that follows. To the accomplishment of the foregoing, the one or more aspects of the present disclosure include the features described and exemplary pointed out in the claims.

Brief Description of the Drawings

[0016] The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more example aspects of the present disclosure and, together with the detailed description, serve to explain their principles and implementations.

[0017] Fig. 1 illustrates a HUD system projecting through a windshield with no wedge angle resulting in a double ghost image;

[0018] Fig. 2(a) illustrates non-polarized light passing through a polarizing filter;

[0019] Fig. 2(b) illustrates reflectance of polarized light (P-waves or S-waves) for soda-lime silicate glass;

[0020] Fig. 3(a) illustrates an example HUD system configured to project P-polarized light to a vehicle windshield for reducing or eliminating ghosting issue, according to an exemplary aspect:

[0021] Fig. 3(b) illustrates another example HUD system configured to project S-polarized light a vehicle windshield for reducing or eliminating ghosting issue, according to an exemplary aspect;

[0022] Figs. 4(a) and 4(b) illustrate images with and without orange peel, respectively;

[0023] Fig. 5 illustrates a system for evaluating a glazing, according to an exemplary aspect;

[0024] Fig. 6 illustrates an area where images may be displayed including a HUD area, according to an exemplary aspect;

[0025] Figs. 7(a), 7(b) and 7(c) illustrate three example parallel line patterns, according to an exemplary aspect;

[0026] Fig. 8 illustrates an example computing device for analyzing images, according to an exemplary aspect; [0027] Fig. 9 illustrates a captured image of a test patern reflected by a specimen glazing, according to an exemplary aspect;

[0028] Fig. 10 illustrates an example pixel range of an image for analysis, according to an exemplary aspect;

[0029] F ig. 1 1 illustrates an example combined contrast image, according to an exemplary aspect;

[0030] Fig. 12 illustrates an example color scale image after conversion, according to an exemplary aspect;

[0031] Figs. 13-15 illustrate measurements results of two samples, according to an exemplary aspect; and

[0032] Fig. 16 illustrates a method for evaluating a glazing, according to an exemplary aspect.

Detailed Description

[0033] Various aspects of invention will be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to promote a thorough understanding of one or more aspects of the invention. It may be evident in some or all instances, however, that any aspects described below can be practiced without adopting the specific design details described below.

[0034] An electromagnetic wave such as light consists of a coupled oscillating electric field and magnetic field which are always perpendicular to each other. By convention, the “polarization” of electromagnetic waves refers to the direction of the electric field. In linear polarization, the fields oscillate in a single direction. In circular or elliptical polarization, the fields rotate at a constant rate in a plane as the wave travels. The rotation may have two possible directions: if the fields rotate in a right hand direction with respect to the direction of wave travel, it is called right circular polarization; if the fields rotate in a left hand direction, it is called left circular polarization. Non- polarized light 202, such as that shown in Fig. 2(a), is generally composed of S-waves and P-waves. As shown, when the non-polarized light 202 is directed to a polarizing filter 204, one type of wave may be blocked. For example, in Fig. 2(a), the polarizing filter 204 shown may eliminate S-waves, allowing only P-waves 206 to pass through the filter 204. The P-waves 206 may then be reflected by a surface 208. For S-waves, the electric field is perpendicular to the plane of incidence (i.e., the plane in which a light ray travels before and after reflection or refraction). For P-waves 206, the electric field is parallel to the plane of incidence, as shown in Fig. 2(a). These polarized waves have different transmitance and reflectance in various materials such as inorganic glass. These properties were described by Fresnel’s equation, in which the values were determined by the refractive indices (i.e., how last light travels through the material). For example, the refractive index of soda lime silicate glass (e.g., defined by ISO 16293-1 : 2008) against air is approximately n = 1 .5 in visible light frequencies. Fig. 2(b) shows reflectance of polarized light to soda lime silicate glass, wherein P-wave light (Rp) has a low reflectance (close to zero) at an angle around 56 deg., known as Brewster’s angle. S-wave light (Rs) has a higher reflectance at the Brewster’s angle compared to P-wave light (Rp). An automotive windshield is usually set at 50-70 deg. to the vertical (or 20 - 40 deg. to the horizontal direction), where the P-waves have low reflection to the glass from an image source.

[0035] Referring to Fig. 3(a), according to aspects of the present disclosure, an example HUD system may be configured to project P-polarized light 310 to a vehicle windshield for reducing or eliminating a ghost image 312. An example automotive laminated glazing (e.g., vehicle windshield structure) may include an outer glass substrate 302, a polymer interlayer 304, a functional layer 306, which may include a reflective polarizing functional layer, and an inner glass substrate 308. The outer glass substrate 302 may have a surface S1 facing a vehicle exterior and surface S2 on an opposite side of the S I surface inside the laminated glazing. The inner glass substrate 308 may have surface S3 inside the laminated glazing and surface S4 as an external side of the glazing facing the inside of the vehicle. When P-polarized light (P-waves) 310 is projected onto the windshield, the projected image 310 may mostly reflect on the functional layer 306 (reflective functional layer). Where the functional layer 306 is a reflective functional layer, there may be more than one reflection to be captured; however, the reflections may not have equal intensity. Ghost images 312 having a smaller intensity than the image 314 may be possible. The functional layer 306 may have unevenness 307 in all or part of the functional layer 306 which may interfere with the image 314 for an observer. Fig. 3(a) shows an embodiment wherein the functional layer 306 may include a functional reflective film which directly reflects P-polarized light efficiently, In other embodiments, a reflective polarizing functional layer may include a quarter wavelength plate (retarder film) and a liquid-crystal based functional reflective film wherein the quarter wavelength plate may change polarization orientation of projected light from P -polarization to circular polarization and the liquid-crystal based reflection film may reflect such circular polarized light efficiently. In some other embodiments a functional layer 306 may be a reflective holographic layer. A holographic film may be used in a glazing to reflect a projected or displayed image.

[0036] Referring to Fig. 3(b), according to other aspects of the presen t disclosure, another example automotive laminated glazing (e.g., vehicle windshield structure) may include an outer glass substrate 302, a polymer interlayer 304, a functional layer 306, which may be a polarization rotation functional layer as shown in Fig. 3(b), and an inner glass substrate 308. The polarization rotation functional layer may be a half wavelength plate (retarder film) which may change polarization orientation from P-pol arization to S-polarization (polarization rotator). When P- polarized light is projected onto the windshield from surface S4, the projected image may mostly reflect on the surface SI after the P-polarized light has pass through a polarization rotation functional layer. Alternatively, as shown in Fig. 3(b), where S-polarized light 316 is projected onto the glazing from surface S4, the projected image 316 may mostly reflect on surface S4 to provide an image 314 to an observer. The functional layer 306 may have unevenness 307 in all or part of the functional layer 306 which may interfere with the image 314 for an observer. Where the functional layer 306 is a polarization rotation functional layer, there may be more than one reflection to be captured; however, the reflections may not have equal intensity. Ghost images 312 may have a smaller intensity than the image 314.

[0037] Referring to Figs. 4(a) and 4(b), for a HUD system implementing a functional layer 306, although the ghosting issue may be reduced or eliminated, the surface defects such as wrinkles, orange peel, dimple, dent, or any other defects including unacceptable film manufacturing direction in the vehicle windshield containing functional layer 306 may affect the image 314 quality where a functional layer 306 is a reflective functional layer or polarization rotation functional layer. Orange peel distortions may include waviness or surface irregularities in a film which may be at a millimeter scale and may cause distortion in a reflected HUD image. Where the functional layer 306 in a windshield is a reflective functional layer, the image quality may be affected relatively more significantly. The reflective functional layer may include, for example, a P-polarized light reflecting layer or a holographic layer. Fig. 4(a) illustrates defects in an image 314 observed compared to the original image in Fig. 4(b). Therefore, among other things, there is a need for detecting the defects which may affect optical quality of vehicle windshield by quantitatively evaluating the quality of the images reflected by the windshield, especially images reflected by the functional layer 306. The term HUD is used herein to refer to display systems, whether employed in the window of a vehicle such as an aircraft, watercraft, or land-craft (including motor vehicles such as automobiles, motorcycles, trucks as well as farming, construction, or industrial machines), in smaller scale systems such as goggle lenses or helmet visors, or in other diverse applications.

[0038] Referring to Fig. 5, according to aspects of the present disclosure, a system 500 for evaluating a glazing may include a specimen 502 (e.g., a laminated glazing such as an automotive windshield), a display (projector) 504, an image capturing device 508 for capturing images reflected off the specimen 502, and a computing device (not shown) for analyzing the captured images in order to detect any defects which may affect optical quality, in the specimen 502,

[0039] Display 504 may be configured to project polarized waves, such as P-waves, onto specimen 502. In one embodiment, display 504, absent a birefringence film, may be configured to control the polarized waves by using a polarizing plate 506. For example, polarized waves may be generated by directing light from display 504 through a polarizing plate or wire-grid polarizer 506, such that a specific polarized light may be passed or filtered. Further, the display 504 may be configured to project a non-polarized or circular light to evaluate defects, such as with a polarization rotation functional layer or a holographic layer. It should be appreciated that the distance from display 504 to specimen 502 may be determined based at least upon the resolution of image analysis and the focus length of the image capturing device 508. Specifically, if the distance is too short, details of the captured images may become less distinguishable. If the distance is too long, it may become impractical to tune the focus of the image capturing device 508 for capturing images. In one implementation, display (projector) 504 may be positioned with a distance to specimen 502 ranging from 150 mm to 1000 mm such that images display in an area of interest, and more preferably around 660 mm, without limitations. Although the area of interest in some disclosed embodiments may involve a HUD area 510 of a vehicle windshield 502, as showm in Fig. 6, system 500 may be applied to an overall vehicle windshield 502. The HUD area 510 is shown with a projected line patern in Fig. 6, but may be positioned in any desired place with any suitable shape on the windshield 502. Moreover, in an embodiment where a projector may be used instead of using a display 504, the distance from the projector to specimen 502 may differ depending upon the focal length of the projector. [0040] Image capturing device 508 of Fig. 5 (e.g., camera) may include at least one optical sensor. For example, a light receiving element, such as a complementary metal-oxide semiconductor (CMOS), a charged coupled device (CCD), or a position sensitive device (PSD) may be used.

[0041] Figs. 7(a). 7(b), and 7(c) show three example parallel line patterns with several frequencies (pitches) to be projected to specimen 502 (i.e., windshield) of Fig. 5. Either straight or curve lines may be applied. A frequency may be defined as the density of line pattern per observer angle. Suitable frequency of parallel lines may depend on size and o r kind of defects which may need to be identified. For example, without limitations, a frequency range of 2 to 60 line pairs (l.p.)/deg. may be used. In one embodiment, when a selected pattern is a parallel line pattern (either straight or curved lines), multiple independent parallel line patterns having a respective pre-determined frequency may be applied. For example, a first parallel line pattern having a first pre-determined frequency may be used for a calibration of reflective brightness, and then a second parallel line pattern having a second pre-determined frequency may be used for an evaluation of defects. The first pre-determined frequency for the calibration may be broader (smaller frequency (l.p./deg. ) ) than the second pre-determined frequency for evaluation of defects. For example, the 1^st frequency for the calibration may be 2 l.p./deg. As shown in Fig. 5, an example measurement set-up may yield Tan θ = a/ L, where a = length of virtual image area 512, and L = distance from the image capturing device 508 to the virtual image 512. Therefore, θ [deg.] = arctan (a/L) and line pattern frequency (l.p./θ) = Number of line pairs / θ [deg.].

[0042] In one embodiment, image capturing device 508 may be a digital single-lens reflex (SLR) camera. An example setting may include: camera (DMC-FZ1000 (Panasonic)); F-number (aperture); 8.0 (=f/8); exposure: ‘4 sec; ISO: 400; image pixel (HxW): 2592 x 3888 pixels; and resolution: 180 dpi. It should be noted that specific setting of image capturing device 508 may depend upon characteristics of specimen 502 and the device 508.

[0043] F-number may be set (eg., the largest number) to achieve optimal image quality/brightaess even in a single photo. Moreover, the range of exposure time may change depending on the ISO or ambient brightness so as the exposure compensation closed to zero or negative values.

[0044] It should be appreciated that images that arc too bright or too dark may lack sufficiently detailed information for subsequent image analysis. Focal point of image capturing device 508 may be adjusted accordingly and images of pattern with several frequencies may be obtained. In one embodiment, a shuter-timer may be used to prevent images from vibrating. Further, instead of using a SLR camera, an imaging photometer, such as LumiCam 2400 imaging photometer- colorimeter by Instrument Systems or ProMetric Y imaging photometer by Radiant Vision Systems, may be used.

[0045] Fig. 8 illustrates an example computing device 800 for analyzing images captured by device 508, in accordance with aspects of the application. Computing device 800 may include a processor 802 configured to couple with memory 804 and control and execute a plurality of modules or circuitry including communication circuitry 806, a pixel range seting module 808, a contrast calculation module 810, a contrast image combination module 812, and a conversion module 814.

[0046] The term “module” or “circuitry” as used herein refers to a real- world device, component, or arrangement of components implemented using hardware, such as by an application specific integrated circuit (ASIC) or field-programmable gate array (FPGA), for example, or as a combination of hardware and software, such as by a microprocessor system and a set of instructions stored in memory 804 to implement the module’s or circuitry’s functionality, which, while being executed, transform the microprocessor system into a special-purpose device. A module or circuitry may also be implemented as a combination of the two, with certain functions facilitated by hardware alone, and other functions facilitated by a combination of hardware and software. In certain implementations, at least a portion, and in some cases, ail, of a module or circuitry can be executed on the processor of a general purpose computer. Accordingly, each module or circuitry may be realized in a variety of suitable configurations and should not be limited to any example implementation exemplified herein.

[0047] Initially, processor 802 may be configured to control and execute communication circuitry 806 to obtain an image captured by device 508, as shown in Fig. 9. Next, a pixel range setting module 808 may be configured to determ ine and set parameters of a pixel range of the image to be calc ulated at once. In some embodiments, suitable parameters of pixel range of the image may be pre-determined and such parameters may be set (received) in the pixel range setting module 808. As shown in Fig. 10, a suitable pixel range of a local area 1002 may depend on the projected images. Such a pixel range 1002 may preferably be a rectangular area. When a selected display pattern is a parallel line pattern (either straight or curved lines), a width of a pixel range may be

generally parallel to the projected line patterns, and. the width of pixel range may be in a range of 1 to 10 pixels. The length of the pixel range may be perpendicular to the projected line patterns, and the length of the pixel range may be configured such that the pixel range length spans at least one line pair. Preferably, the length of the pixel range may be set to span 1.5 line pairs. In certain embodiments, the length of a pixel range may be 5 - 40 pixels. In this manner, the pixel range may include a local maximum and a local minimum of a line pair.

[0048] A contrast calculation module 810 may be configured by processor 802 to calculate a contrast for the set of pixels, where contrast are

the maximum and minimum values, relatively, of brightness which may be in a range of 0 to 255 where 0 indicates black and 255 indicates white. As discussed above, the contrast may be calibrated with data from the broadest line pattern (such as 2 l.p./deg.). Such a contrast calculation for a selected range of pixels may be continued to the next adjacent set of pixels. Once all pixels of the image are covered and scanned, a contrast image combination module 812 may be configured to combine all calculated contrasts into a single gray scale image, as shown in Fig. 11. An optional conversion module 814 may convert the image from gray scale to a color scale one and display information (i.e., maximum contrast) as shown in Fig. 12.

[0049] According to aspects of the present disclosure, as shown in Figs. 9-12, a measurement of a glazing for identifying defects, such as wrinkles or orange peel, which may be present in a functional layer, may focus on contrast loss of narrow lines/patterns of projected images reflected off the glazing (e.g., windshield 502) and/or the local displacement of the lines which is not measured as is, but is the local shift of the lines (i.e., narrower) which will result in lower contrast values after a contrast calculation.

[0050] Referring to Figs. 13- 15, two samples have been measured in accordance with the aspects disclosed above. In Fig. 13, for sample 1, a specimen was prepared as a laminated glazing of 300 x 300 mm flat soda-lime silicate glass substrates laminated with a PVB polymer interlayer together with a reflective polarizing functional layer between the glass substrates. A straight parallel line pattern, as P-waves, was displayed with a line pattern frequency of 10 l.p./deg. (length of pixel range was 30 pixels and width of pixel range was 1 pixel) to reflect on the specimen. Larger size defects may be detectable with a relatively broader frequency (i.e., relatively small value of the line pattern, frequency). In Fig. 14, the straight line pattern frequency for display was set to 40

l.p./deg. ( length of pixel range was 20 pixels and width of pixel range was 1 pixel) for the same specimen used in Fig. 13 (sample 1 ). As shown in Fig. 14, orange peel which was not observed in Fig. 13, can be detected using a relatively narrower frequency (i.e., relatively larger value of the line pattern frequency, such as 40 l.p./deg. compared to 10 l.p./deg.). Fig. 15 shows the measurement results of another specimen (sample 2) which is a full size windshield (about 1000 x 1500 mm) having a three-dimensional bent shape. The display used for sample 2 included a curved line pattern having a line pair frequency of 40 l.p./deg. ( length of pixel range was 20 pixels and width of pixel range was 1 pixel).

[0051] In accordance with another aspect of the present disclosure, to more easily isolate defects, a range of interest, of a glazing under evaluation for surface defects may be control led by tunin g a threshold for a maximum and/or minimum contrast values in a local contrast image, A range of interest may be controlled and selected by adjusting brightness and or contrast in the local contrast image to reveal details at different portions of the image.

[0052] Generally, display of any digital image requires that pixel values (0 - maximum) be allocated a brightness value on a display apparatus. This may be achieved by use of a look up table (LUT) and an example LUT may be a linear translation of pixel values to a display brightness. Based on an analysis of the image's histogram, a range of minimum and maximum (X) and a position of that range in the gray scale intensity space (Y) of the image may be adjusted. Increasing the value of Y may make the image darker, whereas decreasing the value of Y may make the image brighter, X may determine the range of pixel values that maybe incorporated into the display width. Increasing X may reduce display contrast, whereas decreasing X may increase the brightness interval between two consecutive pixel values. Different brightness and/or contrast values may yield details in the glazing under evaluation with different focuses to identify a range of defects.

[0053] Referring back to bigs. 8, 11, and 12, optional conversion module 814 may be configured to convert the image from gray scale to a color scale display- For example, a value of contrast of each pixel range may be in a range of 0 to 1 . Such a value range in a gray scale local contrast image may be assigned to any arbitrary color value and individuals with normal color sensitivity may more readily distinguish subtle differences in color compared to similar differences in gray scale. Use of specific color LUTs may convert a gray scale image into a variety of color maps that may depict quantitative and qualitative changes in the images that are otherwise difficult to discern. In one embodiment, color images contain three separate color intensities (red, green, blue or RGB) that are each stored in one byte with 256 intensity levels, with a total of 3 byte (24 bits) per pixel. A combination of RGB intensities may provide a large number of unique colors (2²⁴= 16.78 million) that may be used to more easily reveal subtle details in an image which indicate surface defects such as wrinkles or orange peel in a glazing that are difficult to detect by visual inspection.

[0054] As a conventional method for evaluating a glazing, modulation transfer function method (MTF) may be based on averaged quantification for an area of interest of the glazing. MTF requires a straight line pattern to be reflected off the specimen glazing, and therefore MTF can allow analysis only over a narrower area since the three-dimensional shape of each area in a curved vehicle windshield is different. That is, for to measure a larger area by MTF, it is difficult to prepare a complicated line pattern to be projected, which must provide a straight line pattern reflected off the glazing in each narrowed area in a windshield. Moreover, in MTF, only averaged quantified value of an area of interest can be obtained and it is difficult to detect localized defects,

[0055] In contrast, as disclosed herein, the present disclosure relates to a local contrast mapping method which calculates a contrast loss of a selected pixel range of an image at once and continues such calculation for all the pixels of the image to generate quantification and mapping of local distortions of a glazing. Among other things, the present disclosure also provides filtering distortion size by projecting a suitable line pair frequency, which may be selected for a identifying distortions of at least a particular size. The present disclosure may allow for the detection of an area of the glazing where the distortion level exceeds an upper limit which may be determined for each line pair frequency based on the HUD image deformation or blurriness.

[0056] Fig. 16 illustrates a method 1600 for evaluating a glazing, according to aspects of the present disclosure. Method 1600 may comprise projecting ( 1602) a test pattern on a specimen glazing and capturing (1604) an image of the test pattern reflected by the specimen glazing. A processor of a computing device (e.g., computing device 800 of Fig. 8) may be configured to determine (1606) a pixel range of the image or use (1606) a pre-determined pixel range and continuously mo ve ( 1608) the pixel range across the entire image for calculating a con trast of each set of pixels included in the pixel range. As a result, a local contrast image (e.g., a gray scale image) may be generated (1610) by the processor of the computing device based on all calculated contrasts and then optionally converted (1612) into a color scale image. Method 1600 may further include identifying (1614) defects in the specimen glazing based at least on the local contrast and/or color scale image. Method 1600 may also include quantifying (1616) the average distortion for the area of interest (e.g., full HUD area) in the specimen glazing based at least on the gray scale and/or color scale image.

[0057] In one embodiment, referring back to Fig. 3(a), a specimen glazing may comprise a first glass substrate 302. a second glass substrate 308, a polymer interlayer 304 between the first and second glass substrates, and a functional layer 306 between the first and second glass substrates. The functional layer 306 may have a reflectivity of at least 1 % for a visible light wavelength at an angle less than 10 degree. Preferably, the functional layer 306 may have a reflectivity of at least 1 %. More preferably, the functional layer 306 may have a reflectivity of at least 5 %,

[0058] The functional layer 306 may comprise a functional film. In one embodiment, the functional film may include a polymer base film and a functional coating, and the polymer base film may be made of polyethylene terephthalate (PET), cellulose triacetate (TAC), polycarbonate, polymethyl methacrylate, polyimide, or any suitable polymer film. PET or TAC may be preferable. The image of the test pattern reflected by the specimen glazing may be captured by a camera, and the functional coating may be positioned between the camera and the polymer base film.

[0059] In another embodiment, the polymer base film of the functional film may have an index of refraction substantially the same as at least one of the first and second glass substrates 302, 308 such that reflection at an interface between the polymer base film and the glass may be reduced or eliminated,

[0060] The functional layer 306 may be part of a HUD system. In one embodiment, the functional layer 306 may be reflective, such as a reflective coating or film specific to a particular polarization of light, such as P-polarized light. In some embodiments, the functional coating or film may include multiple dielectric layers or be liquid crystal based. A liquid crystal coating or film layer may include an oriented liquid crystal, such as a cholestatic liquid crystal, a twisted nematic liquid crystal, or a nematic liquid crystal. In further embodiments, the functional layer 306 may have a function of changing a polarization of light (polarization rotator) to a particular polarization, such as from P-polarized light to S-polarized light. In one embodiment, the functional layer 306 may include an infrared reflective layer or an otherwise functional layer. A functional layer 306 may include a holographic layer. [0061] In one embodiment, the specimen glazing may further comprise an interlayer between the functional layer 306 and the second glass substrate 308, wherein the interlayer has a thickness of 0,1 mm or less.

[00621 In some particular embodiments, the image of the test pattern may be projected as P- polarized light, or by circular polarized light, depending upon specific system implementation. In one embodiment, the image may be projected at an angle within 10 degrees of the Brewster’s angle ( for P-polarized light) of the first glass substrate 302 or the second glass substrate 308.

[0063] Method 1600 of Fig. 16 may further comprise setting, by the processor of the computing device 800 of Fig. 8, a threshold local contrast value for identification of a defect; and identifying the defects in the specimen glazing based on the threshold local contrast. Method 1600 may further comprise calculating an average local contrast over a portion of the image of the specimen glazing,

[0064] Method 1600 may further comprise evaluating the local contrast image to determine orange peel effects caused by the functional layer.

[0065] In one embodiment, the test pattern may comprise a line pattern including parallel lines. In some embodiments, the parallel lines may be arbitrarily oriented including vertically or horizontally oriented in relation to the specimen glazing. Horizontal or vertical orientation may be preferable to reduce complexity of processing to calculate local contrast from the captured images. More preferably, the parallel lines to be projected may be curved. Curvature of the parallel lines may depend on a curvature of the specimen glazing 502 of Fig. 5 (e.g., vehicle windshield having three-dimensional shape) so that straight line patterns will be reflected off the glazing 502, In some embodiments, the image may be more based on a refl ecti on of the functional layer than a refl ection of other surfaces or interfaces of the specimen glazing 502 structure such that a reflective image to be analyzed may relay information about a functional layer 306 laminated in the glazing 502.

[0066] The above description of the disclosure is provided to enable a person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the common principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. For example, the description above may apply to a laminated glazing a well as a single glass substrate. [0067] Furthermore, although elements of the described aspects and/or embodiments may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. Additionally, all or a portion of any aspect and or embodiment may be utilized with all or a portion of any other aspect and/or embodiment, unless stated otherwise. Thus, the disclosure is not to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

Claims:

1 . A method of evaluating a glazing, the method comprising: projecting a test pattern on a specimen glazing; capturing an image of the test pattern reflected by the specimen glazing; determining or obtaining a pixel range of the image; moving the pixel range across the image for calculating a contrast of each set of pixels included in the pixel range; generating a local contrast image based on all calculated contrasts: and identifying defects in the specimen glazing based at least on the local contrast image.

2. The method according to claim 1 , wherein the specimen glazing comprises a first glass substrate, a second glass substrate, a first polymer interlayer between the first and second glass substrates, and a functional layer between the first and second glass substrates.

3. The method according to claim 2, wherein the functional layer has a reflectivity of at least 1 % for a visible light wavelength.

4. The method according to claim 2 or 3, wherein the functional layer comprises a functional film.

5. The method according to claim 4, wherein the functional film includes a polymer base film and a functional coating.

6. The method according to claim 5. wherein the polymer base film is made of polyethylene terephthalate or cellulose triacetate (TAC).

7. The method according to claim 5 or 6, wherein the image is captured by a camera, wherein the functional coating is positioned between the camera and the polymer base film.

8. The method according to any of claims 5 to 7, wherein the polymer base film has an index of refraction substantially the same as at least one of the first and second glass substrates.

9. The method according to any of claims 2 to 8, wherein the functional layer is part of a head- up display system.

10. The method according to any of claims 2 to 9, wherein the functional layer reflects P- polarized light.

11 . The method according to any of claims 2 to 10, wherein the functional layer includes an infrared reflective layer.

12. The method according to any of claims 2 to 9, wherein the functional layer is a polarization rotator.

13. The method according to claim 12, wherein the functional layer includes a liquid crystal layer.

14. The method according to any of claims 2 to 10, wherein the functional layer includes a holographic layer.

15. The method according to any of claims 2 to 3 or 9 to 13, wherein the functional layer includes a functional coating.

16. The method according to any of claims 2 to 15, wherein the specimen glazing further comprises a second interlayer between the functional layer and the second glass substrate, wherein the second interlayer has a thickness of 0.1 mm or less.

17. The method according to any of claims 1 to 16, wherein the image is projected with P- polarized light.

18. The method according to any of claims 1 to 16, wherein the image is projected with circular polarized light.

19. The method according to any of claims 2 to 18, wherein the image is projected at an angle within 10 degrees of the Brewster’s angle of at least one of the first glass substrate and the second glass substrate.

20. The method according to any of claims 1 to 19, further comprising: setting a threshold local contrast value for identification of a defect; and identifying the defects in the specimen glazing based least on the threshold local contrast.

21. The method according to any of claims 1 to 20, further comprising calculating an average local contrast over a portion of the image of the specimen glazing.

22. The method according to any of claims 4 to 14 or 16 to 21, further comprisi ng evaluating the local contrast image to determine orange peel effects caused by the functional film.

23. The method according to any of claims 1 to 22, wherein the test pattern comprises a line pattern.

24. The method according to claim 23, wherein the line pattern includes parallel lines.

25. The method according to claim 24, wherein the parallel lines are vertically oriented in relation to the specimen glazing.

26. The method according to claim 24, wherein the parallel lines are horizontally oriented in relation to the specimen glazing.

27. The method according to any of claims 2 to 26, wherein the image is more based on a reflection of the functional layer than any other surface of the specimen glazing.

28. The method according to any of claims 1 to 27, wherein determining the pixel range of the image is performed by a processor of a computing device.

29. The method according to any of claims 1 to 28, wherein the local contrast image is a color scale image.

30. A method of evaluating a glazi ng, the method comprising: projecting a test pattern on a specimen glazing; capturing an image of the test pattern reflected by the specimen glazing; determining or obtaining a pixel range of the image; moving the pixel range across the image for calcula ting a contrast of each set of pixels included in the pixel range; generating a local contrast image based on all calculated contrasts; converting the local contrast image into a color scale image; and identifying defects in the specimen glazing based at least on the color scale image.

31. A system for evaluating a glazing, the system comprising: a display configured to project a test pattern on a specimen glazing; an image capturing device configured to capture an image of the test pattern reflected by the specimen glazing; and a computing device including a processor configured to: determine a pixel range of the image or obtain a pre-determined pixel range of the image; move the pixel range across the image for calcula ting a contrast of each set of pixels included in the pixel range; generate a local contrast image based on all calculated contrasts; and identify defects in the specimen glazing based at least on the color scale image.

32. A non-transitory computer-readable medium comprising code that, when executed by a processor of a computing device, causes the processor to perform: obtaining an image of a test pattern projected on and reflected by a specimen glazing; determining a pixel range of the image or obtaining a pre-determined pixel range of the image; moving the pixel range across the image for calculating a contrast of each set of pixels included in the pixel range;

generating a local contrast image based on all calculated contrasts; and identifying defects in the specimen glazing based at least on the color scale image.