WO2022064518A1

WO2022064518A1 - A method and system to quantify the impact of a tinted glazing on perceived brightness by a human eye

Info

Publication number: WO2022064518A1
Application number: PCT/IN2021/050925
Authority: WO
Inventors: Vinay NATRAJAN; Sreeja S
Original assignee: Saint-Gobain Glass France
Priority date: 2020-09-23
Filing date: 2021-09-21
Publication date: 2022-03-31

Abstract

A method and a system to quantify the impact of a tinted glazing on perceived brightness by a human eye are disclosed. The method quantifies glare as a function of photopic spectrum of the human eye and non-linear response of the human eye to brightness. The light that is perceived by the human eye through the glazing is a convolution of the transmission spectrum with the incident spectrum of daylight and the photopic response of the human eye. The method demonstrated that a blue-tinted glazing surprisingly recorded less perceived brightness (L*) to the human eye when compared to a neutral-tinted (both glazing having identical %VLT) disproving the widely known popular belief that two glazing having the same level of visible light transmission would have a similar effect on glare, thanks to the method that quantifies glare not as a function of intensity of incident light but as a function of photopic spectrum of the human eye and non-linear response of the human eye to brightness.

Description

A METHOD AND SYSTEM TO QUANTIFY THE IMPACT OF TINTED GLAZING ON PERCEIVED BRIGHTNESS BY A HUMAN EYE

Technical Field

The present invention generally relates to a glare measurement technique and a system specifically configured to quantify the perceived brightness by a human eye. More particularly, the present invention relates to a method and system to quantify the impact of tinted glazing on perceived brightness by the human eye.

Background

Energy efficiency and well-being are major challenges existing in the construction industry lately. Due to the growing interest in these aspects, discomfort glare indices are becoming more significant and are being increasingly used. On one hand, specialized glazing such as solar control glass, coated glass, tinted glazing and other glazing solutions that cut down heat and light have a large part to play in the future of construction, as external temperatures will continue to rise and so will the expectations of comfort. On the other hand, office building windows are optimized to maximize the amount of daylight and a large amount of glazing implies an increased risk of discomfort glare. Thus recommendations to reduce glare or limit discomfort glare from daylight is gaining a lot of traction.

With regard to visual comfort management, control models implemented in this kind of systems, widely aim to use indices such as Daylight Glare probability (DGP) and Unified Glare Rating (UGR). Thresholds of visual discomfort are predetermined in these indices so that glazing solutions not exceeding these thresholds can be identified and installed. Almost all existing recommendations to limit discomfort glare from daylight use Daylight Glare probability (DGP) as a reference index. However, the DGP metric takes into account only the intensity of the total light transmitted through the glazing and not the spectrum of light received by the eye. This is particularly a limitation when DGP is used to determine discomfort glare of glazing solutions that transmit identical intensities of the light source into the building. Therefore, DGP cannot quantify the difference in glare perception between the two glazings that exhibit same visible light transmission (VLT) but differ in their tint which contributes to the difference in glare perception when viewed by a person.

Referring to JP application JP2004061150 relates to a prediction method that uses Unified Glare Rating (UGR) to evaluate glare levels based on light intensity, position of light source and angle of light source. Reference is also made to Japanese applications JP2007292665 & JPS6447916; US publication number 2015/0035972 and PCT publication number WO2013150830, all of which relate to glare measurement devices and systems. However, all these inventions relate to luminance based evaluation of glare that use light intensity to calculate glare. They do not evaluate the difference in glare perceived due to the difference in the color of view or the spectrum of incoming light.

Anti-glare devices that adjust the intensity of the emitted light from an external light source into the human eye according to the information of the human eye are also known in the art. Referring to PCT publication number 2019/184917 provides one such device for controlling discomfort glare where the light adjusting member regulates the transmitted light intensity based on the pupil response of the eye which contracts or dilates based on the intensity. While the patent offers to reduce the intensity of light with the use of tinting filters in order to reduce discomfort glare, it fails to actively quantify glare.

Thus notwithstanding all the evaluation indices available for glare detection, there is still a need in the art to quantify glare as a function of light spectrum received by the human eye and not as just as a function of light intensity. A method that quantifies glare as a function of the light spectrum received by the eye will especially be useful when determining glare perception of glazings that have identical light intensities but different tint, as these glazing demonstrate identical DGP values, thanks to their identical visible light transmission (VLT). It is thus a purpose of this invention to propose a method and a system that make it possible to quantify a difference in perception of glare as a result of the tint of the glazing, details of which will become apparent to the skilled artisan once given the following disclosure.

The present invention uses an image processing device to scale the images of a tinted glazing based on the light spectrum received by the eye and response of the human eye to the light spectrum. Certain embodiments of this invention relate to a method that quantifies impact of glazing tint on perceived brightness or glare perception by the human eye while certain other embodiments of this invention relate to a system that is specifically configured to carry out the method outlined for quantifying perceived glare by the human eye.

Summary of the Invention

In one aspect of the present invention, a method to quantify the impact of a tinted glazing on perceived brightness by a human eye is disclosed. The method comprises the steps of: imaging a tinted glazing at multiple exposure levels of a view taken within a measurement zone fitted with the glazing; building a high dynamic range (HDR) image by merging all the images captured at various exposure levels; measuring luminance within the measurement zone at periodic intervals in a day; calibrating the HDR image with the measured luminance values; scaling the HDR image with respect to the photopic spectrum of the human eye and non-linear response of the human eye to brightness and calculating the perceived brightness of the colors in the HDR image by the human eye. The scaling of HDR image involves extraction of red, green and blue channels from the HDR image, decoupling the chromaticity from the luminance information in the image, and scaling them to match the human perception of brightness in daylight.

In another aspect of the present invention, a system for measuring the impact of tinted glazing on perceived brightness by a human eye is disclosed. The system comprises of an imaging device that captures images of a tinted glazing unit at multiple exposures of a view taken within a measurement zone fitted with the glazing units; a luminance meter to measure luminance within the measurement zone and an image processing device. The image processing device is configured to build a high dynamic range (HDR) image, calibrate the HDR image with luminance value and scale the HDR image with respect to the photopic spectrum of the human eye and non-linear response of the human eye to brightness.

Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

Brief Description of the Drawings

Embodiments are illustrated by way of example and are not limited to those shown in the accompanying figures.

FIG. 1 illustrates a flow chart of the steps involved in a method to quantify the impact of a tinted glazing on perceived brightness by a human eye, according to one embodiment of the present invention;

FIG. 2 illustrates a plot of the perceived brightness L* in the pixels of an image, according to an example embodiment of the present invention;

FIG. 3 illustrates block diagram of a system configured to carry out the method disclosed in the invention, according to another embodiment of the present invention;

FIG. 4A depicts the images processed and the corresponding perceived brightness plot of two clear glazing installed in measurement zone A and B;

FIG. 4B illustrates the plot of multiple datasets of perceived brightness (L*) of clear glazing installed in measurement zone A and B at periodic intervals of the day;

FIG. 5A depicts the images processed and the corresponding perceived brightness plot of blue tinted glazing and neutral tinted glazing installed in measurement zone A and B ; and

FIG. 5B illustrates the plot of multiple datasets of perceived brightness (L*) of blue tinted glazing and neutral tinted glazing installed in measurement zone A and B at periodic intervals of the day.

Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the invention.

Detailed Description

Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or similar parts. Embodiments disclosed herein are related to a method to quantify the impact of a tinted glazing on perceived brightness by a human eye and a system configured to carry out the steps of the below described method.

“Measurement zone” as used herein in this invention is defined as a closed target area fitted with a single, south-east-oriented glazing exposed to the natural sky that allows a pre-determined amount of light and heat from the external environment to the inside of the target area. The target area simulated an idealistic/extreme case where the interior surfaces are entirely white. The “perception of brightness by the human eye” / “glare perception by the human eye” as described herein are interchangeably used to refer to the loss of visual performance or discomfort produced by an intensity of light in the visual field greater than the intensity of light to which the human eyes are adapted.

When light through a glazing is being viewed by a person, a combination of physical, physiological and cognitive factors come into play viz., the spectrum of the light source incident upon the glazing; the material properties of the glazing determining the transmission spectrum through the glazing; and the response by the human eye to the transmitted light. It is the combination of these factors that influence how the human eye perceives the transmitted light. These factors also contribute to the human perception of brightness or glare of light observed through the glazing. Thus in the context of glare perception by the human eye, it is necessary to capture and quantify the effect of the photopic response of the human eye on the light perceived by it.

The spectral distribution of light that passes through a glazing that has no tint differs considerably from when the light that passes through a glazing that has a tint either from the glass composition or coating materials provided on the surface of the glass. As a result of which two tinted glazing although having a similar total visible transmission would bring light of different spectral content to the human eye and thus may change his or her visual performance or perceived glare. Glare is produced by brightness within the field of vision that is sufficiently greater than the luminance to which the eyes are adapted so as to cause annoyance, discomfort, or loss in visual performance and visibility. Discomfort glare is the sensation of annoyance or pain that is felt in the presence of bright light and relates greatly to the spectral contents of the light source.

Contrary to popular belief that two glazing having the same level of visible light transmission would have a similar effect on glare, the method described in the present invention yielded surprising results, with a blue tinted glazing recording less average perceived brightness (L*) to the human eye when compared to that of a neutral tinted glazing, in spite of both the glazing having the same level of visible light transmission. The above finding was further corroborated by a survey conducted by the inventors among 192 respondents comprising of architects, designers, and engineers.

If popular glare indices such as Daylight Glare probability (DGP) were to be used to determine the discomfort glare associated with differently tinted glazings that have a similar total visible transmission, then their DGP values would also be similar as the calculation only takes into account the intensities of the incoming light from the two differently tinted glazing. That is why inventors of the present invention have derived a methodology to calculate the glare associated with differently tinted glazings having the same total visible transmission using two factors viz., photopic spectrum of the human eye and non-linear response of the human eye to brightness.

The inventors set out by choosing two glazing for a comparative study to understand the impact of tint on glare perception by the human eye: a blue- tinted substrate and a neutral-tinted substrate. The two sample substrates had equal total visible light transmission % (VLT) of ~ 38%. A double glazing unit (DGU) comprising the blue-tinted substrate and a DGU comprising the neutral-tinted substrate were installed in the separate measurement zones A, B, respectively and images of the glazing were acquired simultaneously over a period of 3 months to measure DGP using an HDR imaging technique. The measurements were carried out through various times of the day, cloud cover and different months of the year.

FIG. 1 illustrates a flowchart depicting a method 500 to quantify the impact of tint of the glazing on perceived brightness by a human eye. The method 500 comprises of the following steps:

Step 510: camera images were acquired simultaneously in measurement zones A and B fitted with the blue-tinted glazing and neutral-tinted glazing at multiple exposure levels over a period of 3 months through various times of the day, cloud cover and different months of the year. The workings of a camera mimic the human eye in several ways, yet it does not do so entirely. One of the similarities of a camera to a human eyeball is the anatomy: lens-like cornea and the film-like retina. The variable aperture/shutter speed mimics the iris in controlling the amount of light falling on the image sensor. By using a Fish-eye lens which has a field of view of 180°, the field of vision of a human eye which ranges from 160° -180° can be approximately mimicked.

According to one embodiment of the method of the present invention, the images were captured using a shutter speed ranging between 4 to 1/1800 seconds at Fl l aperture and a sensor sensitivity at ISO 100. It should be noted that the method can be used to determine the glare perception by the human eye of any tinted glazing or non-tinted (clear) glazing and the above mentioned comparative study using a blue-tinted substrate and a neutral-tinted substrate having similar VLT has been demonstrated only as an example to aid in understanding the teachings of the present invention and not in any manner to limit the scope of the present invention.

According to yet another embodiment of the present invention, the tinted glazing referenced herein may comprise a glazing substrate provided with a solar-control coating that cuts down heat transfer from the external environment and allows pre-determined level of visible light transmission inside the measurement zone. According to still another embodiment of the present invention, the tinted glazing referenced herein may comprise a glazing substrate that exhibits a tint as a result of the glass composition used for its manufacture. Step 520: images of the blue-tinted glazing and neutral-tinted glazing captured at multiple exposures are merged together using conventional tools or platforms to build a high dynamic range (HDR) image. In one embodiment, the images obtained in step 510 are manually stitched together for building an HDR image. Alternatively, the step can be performed automatically as will be outlined in the later part while outlining a system 600 configured to carry out the method steps of the present invention.

Step 530: luminance levels inside the measurement zones A and B fitted with the blue-tinted glazing and neutral-tinted glazing are measured over a period of 3 months through various times of the day, cloud cover and different months of the year. The luminance levels inside the measurement zone fitted with the blue-tinted glazing was found to be identical with the luminance levels measured inside the measurement zone fitted with the neutral-tinted glazing. This is owing to the two glazings having a similar %VLT. Therefore, when DGP was determined for the two glazings, their DGP values were also found to be similar. As described earlier, the DGP metric is a function of the luminance of the light source, which implies that it takes into the increase in the amount of light in the field of vision. Since the %VLT of the two glazings are equal to -38%, the amount of light entering the measurement zone is the same in both cases. This is why the DGP was observed to be equal for both the glazings.

The HDR imaging technique for DGP utilizes the similarities between the human eye and a camera in terms of the view of the image captured and the variation in the scene luminance captured in the HDR image. While this method is effective in estimating the DGP which is a function of the total luminance, it does not account for the wavelength based differences in perception of brightness by the human eye.

Step 540: HDR image obtained is then calibrated with the luminance vales measured in step 530. In one embodiment, the calibration is done manually. Alternatively, the calibration can be done automatically as will be outlined in the later part while outlining a system 600 configured to carry out the method steps of the present invention. Step 550: In order to accurately quantify how the human eye perceives the difference in brightness between the neutral and blue-tinted glazing, it is necessary to scale the HDR images with respect to the photopic spectrum of the human eye. According to one embodiment of the present invention, this is done by extracting the Red, Green, and Blue (RGB) channels from the HDR images. This step reads the HDR images and extracts the R G and B values into separate matrices and normalizes them to a scale of 0-100. Scaling the HRD image will help in determining the perceived brightness of the colors in the image of the view through the measurement zones A and B. The RGB axes are based on three actual colors which can be used in combination to produce a large range of colors.

Step 560: R G B axes are converted to X Y Z coordinates, respectively by decoupling the chromaticity from the luminance in the HDR image using linear transformations. This process converts R G B coordinates to the X Y Z coordinates corresponding to the extracted R G B values. The axes of X Y Z were chosen so that Y represented the luminance, and X and Z the range of colors having the corresponding luminance values in the Y data set.

Step 570: scaling of X Y Z values obtained in step 560 to match the human eye perception of brightness in daylight including the non-linear response of the eye at high and low stimuli is done. In this step, the X Y Z values are scaled based on a typical color value for sunlight, which is (0.95047, 1.0, 1.08883), called illuminant D65 (with a CCT = 6500 K). A luminance level is selected to represent white (like the white point of a display) and then the absolute tri-stimulus values are normalized to that point. Conditional statements are used in the algorithm to cover the non-linear response of the eye at high and low stimuli.

Step 580: scaled values of X Y Z are then used for calculating L*, a* and b* values that represent accurately the perceptual distance between colors and their corresponding perceived brightness. This provides the color distribution in the HRD images of the view and the corresponding brightness perceived of the colors by the human eye. The perceived brightness L*, the color distribution in the HDR image i.e., redness-greenness dimension a* and yellowness-blueness dimension b* are calculated using previously established relationships according to multiple specific embodiments of the present invention. The Experimentally determined multiplication factors from literature are used in the equations to make the physical distance between colors and their corresponding brightnesses match with the perceptual distance between them as well.

A sample plot of the perceived brightness L* in the pixels of an image is shown in FIG. 2, according to an example embodiment. The plot shows the average perceived brightness of the colors in each row of pixels. The perceived brightness is given for each color in the images of the facades. The brightest spot can be seen to have a L* value of 1 and the least bright spot can be seen to have a L* value of 0.

FIG. 3 illustrates a block diagram of a system 600 specifically configured to carry out the method steps outlined in the present invention, according to an example embodiment of the present invention. The system 600 comprises of an imaging device 610, a luminance measuring meter 620 and an image processing device 630. The first major component of the system 600, the imaging device 610 according to an example embodiment of the present invention is a camera fitted with a Fish-eye lens having a field of view of 1800, the field of vision of a human eye which ranges from 1600 -1800. In another embodiment, a DSLR camera fitted with 180° Field of View fish eye lens can be employed. The shutter speed ranging between 4 to 1/1800 seconds at Fl l aperture and a sensor sensitivity at ISO 100 is controlled manually to obtain images of the measurement zone fitted with the tinted glazing for over a period of 3 months through various times of the day, cloud cover and different months of the year.

The CMOS sensor of the camera mimics the human eye in the way that it has 3 bands of sub-pixels responding to 3 wavelength bands in the visible spectrum, i.e. Blue, Green, and Red. However, there is a key aspect that is considerably different from the human eye, possibly due to material or fabrication constraints of the image sensor in the camera.

The second major component of the system 600 is the luminance measuring unit 620 that captures the luminance inside the target area of the measurement zone fitted with the glazing. The third major component of the system 600 is the image processing device 630 which in turn comprises of an image pick up unit 631 that receives the images captured by the imaging device 610; an image composition unit 632 and perceived glare calculator unit 633. The image composition unit 632 is configured to receive the images from the image pick up unit 631 and further receive the luminance values from the luminance measurement unit 620. The image composition unit 632 is comprised of a HDR image builder, a luminance calibration unit and an image generator.

The HDR image builder stitches all the images received by the image composition unit 632 to generate a HDR image which is picked up by the luminance calibration unit in order to calibrate the HDR image with all the luminance values measured over the period. The image generator presents the calibrated HDR image, which is then picked up by the perceived glare calculator unit 633. The glare calculator unit 633 in turn is comprised of R G B channel extraction unit, normalization unit, decoupling unit and photopic spectrum response scaling unit for carrying out respectively the steps described in steps 550 - 580.

In one embodiment of the present invention, the system 600 comprises the above mention three major components. In few other embodiments, as the one described in FIG. 3, the system 600 further comprises of a display unit 640 that displays the perceived brightness of the image to the eye L* and the color distribution of the image through a* and b* values. Alternatively, system 600 may be configured without a display unit.

Although the system for carrying out the method described in the present invention has been explained by way of the illustrated system 600 comprised of the above said units/ components, the scope of the present invention is in no manner limited by said system 600. The described system 600 is merely used for the purposes of teaching the present invention. Any alternations or modification to the unit/components described above are well within the scope of the present invention as long as the unit/components carry out steps that arrive at the method described herein.

Examples Comparative Example 1

Perceived Brightness by The Human Eye of Identical Clear Glazing:

In order to validate the method to quantify the perceived brightness by the human eye, a comparison between the images acquired from 2 measurement zones A, B installed with identical clear glazing were done. The images processed and the corresponding perceived brightness plot are shown in FIG. 4A. The perceived brightness plots of both the images mostly overlap indicating that the perceived brightness of the images of the views through the two identical clear glazing is the same, as it should be. Further data comparing multiple datasets of average perceived brightness from the two measurement zones A, B with identical glazing are shown in FIG. 4B, where the values are almost equal in all cases. Thus the method is validated and can be used to quantify and compare the perceived brightness of views through different glazing.

Example 1

Comparison of Perceived Brightness of Blue-Tinted Glazing & Neutral-Tinted Glazing:

To quantify the difference in perceived brightness between the blue-tinted glazing and the neutral-tinted glazing, the images acquired of the views when the two glazing were installed in the measurement zones A and B were processed using the above-described steps. Two sample datasets of the processed images and the comparison plot of the perceived brightness are shown in FIG. 5A. And the combined plot of comparison of average perceived brightness through both the glazing is shown in FIG. 5B.

The results show that the perceived brightness of colors in the image of blue-tinted glazing is lower than that in the image of neutral- tinted glazing. This can be explained to be the result of three factors: the daylight spectrum, transmission spectra of the glasses and the photopic spectrum of the human eye. Even though the blue-tinted glazing and neutral-tinted glazing had equal %VLT of -38%, the blue-tinted glazing has a transmission spectrum with the lesser transmission in the yellow-green wavelengths, and higher transmission in the blue wavelength region; whereas the vice-versa is true for the neutral-tinted glazing. The light that is perceived by the human eye through the glazing is a convolution of the transmission spectrum with the incident spectrum of daylight and the photopic response of the human eye. The peak response of the human eye is at 555 nm (green-yellow wavelength region), with the lowest sensitivity for blue wavelengths. Moreover, a survey of daylight spectra in tropical climates shows that the daylight spectra shows attenuation of blue-wavelength light, with a higher fraction of light reaching the surface being in the green- yellow wavelengths. Given the above-described factors, i.e., the spectrum of daylight observed in luminous tropical climates, the transmission spectra of the tinted glazing and the response of the human eye, the light observed through blue-tinted glazing is perceived as less bright than that observed through neutral- tinted glazing.

Industrial Applicability

The method described herein can be used to quantify perceived brightness of the human eye by any glazing of the type including monolithic, DGU, TGU, clear or tinted or coated glazing. However, particularly the method is useful while determining glare perception of glazing that have same %VLT, for which the widely used glare indices DGP are similar.

Note that not all of the activities described above in the general description or the examples are required, that a portion of a specific activity may not be required, and that one or more further activities may be performed in addition to those described. Still further, the order in which activities are listed is not necessarily the order in which they are performed.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any feature(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature of any or all the claims.

The specification and illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The specification and illustrations are not intended to serve as an exhaustive and comprehensive description of all of the elements and features of apparatus and systems that use the structures or methods described herein. Certain features, that are for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in a sub combination. Further, reference to values stated in ranges includes each and every value within that range. Many other embodiments may be apparent to skilled artisans only after reading this specification. Other embodiments may be used and derived from the disclosure, such that a structural substitution, logical substitution, or another change may be made without departing from the scope of the disclosure. Accordingly, the disclosure is to be regarded as illustrative rather than restrictive.

The description in combination with the figures is provided to assist in understanding the teachings disclosed herein, is provided to assist in describing the teachings, and should not be interpreted as a limitation on the scope or applicability of the teachings. However, other teachings can certainly be used in this application.

As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a method, article, or apparatus that comprises a list of features is not necessarily limited only to those features but may include other features not expressly listed or inherent to such method, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive-or and not to an exclusive-or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

Also, the use of "a" or "an" is employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural, or vice versa, unless it is clear that it is meant otherwise. For example, when a single item is described herein, more than one item may be used in place of a single item. Similarly, where more than one item is described herein, a single item may be substituted for that more than one item.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples are illustrative only and not intended to be limiting. To the extent that certain details regarding specific materials and processing acts are not described, such details may include conventional approaches, which may be found in reference books and other sources within the manufacturing arts.

While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.

List of Elements

TITLE: A METHOD AND SYSTEM TO QUANTIFY THE IMPACT OF TINTED GLAZING ON PERCEIVED BRINGTHNESS BY A HUMAN EYE

500 Method

510 Step

520 Step

530 Step

540 Step

550 Step

560 Step

570 Step

580 Step

600 System

610 Imaging device

620 Luminance Measuring Unit

630 Image Processing Unit

631 Image Pick Up Unit

632 Image Composition Unit

633 Perceived Glare Calculator

640 Display Unit

Claims

We claim,

1) A method to quantify the impact of a tinted glazing on perceived brightness by a human eye comprising the steps of: imaging a tinted glazing at multiple exposure levels of a view taken within a measurement zone fitted with the glazing; building a high dynamic range (HDR) image by merging all the images captured at various exposure levels; measuring luminance within the measurement zone at periodic intervals in a day; calibrating the HDR image with the measured luminance values; scaling the HDR image with respect to the photopic spectrum of the human eye and non-linear response of the human eye to brightness; and calculating the perceived brightness of the colors in the HDR image by the human eye, wherein scaling of HDR image involves extraction of red, green and blue channels from the HDR image, decoupling the chromaticity from the luminance information in the image, and scaling them to match the human perception of brightness in daylight. ) The method as claimed in claim 1, wherein the step of scaling HDR image with respect to the photopic spectrum of the human eye and non-linear response of the human eye to brightness comprises: converting the extracted red, green and blue values to XYZ coordinates by decoupling the chromaticity from the luminance information in the image using a linear transformation matrix; and calculating L* (perceived brightness), a* (redness-greenness) and b* (yellowness-blueness) values from the XYZ coordinates, wherein Y in the XYZ coordinates represents the luminance value, X and Z represent the range of colors at a given luminance value. ) The method as claimed in claim 2, wherein a* and b* values are used for determining the color distribution in the HDR image and L* values are used for determining the perceived brightness of the colors. ) The method as claimed in claim 1 or claim 2, wherein the perceived brightness of the colors in the HDR image by the human eye is calculated by averaging the value of L* for every row of pixels, wherein the brightest spot has an L* value of 1 and the least bright spot have an L* value of 0. ) The method as claimed in claim 1, wherein the multiple exposure levels for image capturing are obtained using a shutter speed ranging between 4 to 1/1800 seconds at Fl l aperture and sensor sensitivity at ISO 100. ) The method as claimed in claim 1, wherein the tint in the glazing is obtained as a result of a coating technique or is obtained from the composition of the glass used for making the glazing. ) The method as claimed in claim 1, wherein the tinted glazing may comprise a solar-control coating that cuts down heat transfer from the external environment and allows pre-determined level of visible light transmission inside the measurement zone. ) A system for measuring the impact of tinted glazing on perceived brightness by a human eye, the system comprising: an imaging device that captures images of a tinted glazing unit at multiple exposures of a view taken within a measurement zone fitted with the glazing units; a luminance meter to measure luminance within the measurement zone; and an image processing device configured to: build a high dynamic range (HDR) image by merging images captured by the imaging device; automatically calibrate the HDR image with the luminance value; scale the HDR image with respect to the photopic spectrum of the human eye and non-linear response of the human eye to brightness; and calculate the perceived brightness of the colors in the HDR image by the human eye, wherein scaling of HDR image involves extraction of red, green, and blue channels from the HDR image, decoupling the chromaticity from the luminance information in the image, and scaling them to match the human perception of brightness in daylight. ) The system as claimed in claim 8, wherein the imaging device is a DSLR camera fitted with 180° Field of View fish eye lens. 0) The system as claimed in claim 8, wherein the processing device is further configured to display the value of the perceived brightness of the colors in the HDR image by the human eye.

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