Council for Optical Radiation Measurements (CORM) 2016 Annual Technical Conference May 15 18, 2016, Gaithersburg, MD

Council for Optical Radiation Measurements (CORM) 2016 Annual Technical Conference May 15 18, 2016, Gaithersburg, MD Multispectral measurements of emissive and reflective properties of displays: Application to outdoor performances and physico-realistic ray tracing simulations Pierre BOHER, ELDIM, 1185 rue d Epron, 14200 Hérouville St Clair, France Email: pboher@eldim.fr Tel : 33 2 31 94 76 00 Slide #1

Outline 1. Introduction: Purpose of the study 2. Experimental technique a) Emissive properties b) Reflective properties i. Collimated beam spectral BRDF ii. Full diffused spectral reflectance 3. Experimental results a) Reflective properties of a metallic surface b) LCD with variable top polarizer c) OLED display 3. Ray-tracing simulations 4. Conclusions Slide #2

Introduction Slide #3

Part I: Introduction All displays used outdoor suffer from parasitic reflections that affect their contrast and luminance properties. This is always the case for mobile applications like phone cell displays or tablet displays. For automotive applications it can be critical since parasitic illumination can have a direct impact of the security Purpose of the paper is to quantify these imperfections to be able to: Compare displays efficiently Realize physico-realistic display simulations Slide #4

Part I: Introduction Specular included Specular excluded Standard way to measure display under external illumination: hemispherical reflection with or without specular (IDMS section 11.3) Main drawbacks: Fixed illumination conditions (spectral content and geometry). Fixed detection geometry Additional specular source possible but with increasing complexity Strategy of the study: Make Spectral and normalized measurements of the reflective properties Measure full diffused and collimated beam illumination independently Slide #5

Part I: Introduction The Emissive Properties E(θ e, φ e, GL): Color or luminance for each pixel (θ e, φ e ) direction of emitted beam GL grey level of the pixel The spectral reflectance R(θ r φ r, λ) using full diffused illumination (θ r, φ r ) direction of reflected beam λ wavelength dependence The BRDF (θ I, φ I, θ e, φ e, λ) using collimated illumination: (θ I, φ I ) direction of incidence beam (θ e, φ e ) direction of reflected beam λ wavelength dependence Mandatory for simulation of color images Mandatory for simulation under any illumination conditions Slide #6

Experimental techniques Slide #7

Part II: Experimental techniques Angular aperture & spot size are controlled independently Multispectral measurement with 31 band-pass filters Slide #8

Part II: Experimental techniques Transmittance (%) 70.00 60.00 50.00 40.00 30.00 20.00 10.00 0.00 350 400 450 500 550 600 650 700 750 Wavelength (nm) 400nm 410nm 420nm 430nm 442nm 450nm 458nm 467nm 480nm 488nm 500nm 510nm 520nm 532nm 540nm 550nm 568nm 580nm 589nm 600nm 610nm 620nm 632nm 640nm 647nm 650nm 656nm 671nm 676nm 690nm 694nm Principle : 1. 31 band pass filter measurements from 400 to 700nm 2. 10nm wavelength resolution 3. ±88 incidence & 2mm spot size 4. Luminance and color can be computed Slide #9

Part II: Experimental techniques Collimated or full diffused illuminations can be applied Multispectral measurement is made with 31 band pass filters Slide #10

Part II: Experimental techniques Full diffused reflectance measurement The spectral reflectance is full diffused illumination is given by dlr ( θr, ϕr, λ) R ( θr, ϕr, λ) = dl ( θ, ϕ, λ) (θ r,φ r ) is the polar coordinates of the detection direction dl r and dl w are the radiance measured on sample and Spectralon R White is the reflection coefficient of the Spectralon Parasitic reflections are corrected using a light trap White r r z dω r Incident beam θ r Reflected beam φφ r y x Measured directly by the instrument Slide #11

Part II: Experimental techniques Collimated beam spectral BRDF measurement The spectral BRDF is collimated beam illumination is given by dlr ( θr, ϕr, λ) BRDF ( θi, ϕi, θr, ϕr, λ) = de ( θ, ϕ, λ) dl r is the radiance diffused by the sample de i is the irradiance of the sample i i i Incident beam dω i BRDF( θ, ϕ, θ, ϕ, λ) = i i r r R 2πStr white φφ i θ i z ( θ, λ) L θ r r dω r i, θr, ϕr, Reflected beam λ)cosθ dω L White is the radiance measured on spectralon and R White its reflection coefficient r dl r White ( θ, ϕ, λ) i r ( θ, ϕ r r φφ r y x Measured directly by the instrument Slide #12

Calibration of the BRDF measurements 10.00 10 20 30 40 50 60 70 75 80 1.00 BRDF (sr-1) 0.10 Spectralon is not Lambertian at high incidence angles 0.01-90 -60-30 0 30 60 90 Angle (deg) Measurements on the white Spectralon sample For different incidence angles and versus the detection angle in the incidence plane Slide #13

Part II: Experimental techniques CCD camera Band pass filters Optical fiber Additional optics Fourier optics Sample Power supply Xenon lamp Setup for BRDF measurements May 16 th, 2016 Slide #14

Experimental results Slide #15

Part III: Anisotropic metallic surface Brushed copper sample with transparent layer protection Slide #16

Part III: Anisotropic metallic surface Purple Zone Reflectance pattern vs wavelength Yellow Zone Spectral reflectance in full diffused illumination of Cu sample Protection layer has not the same thickness Slide #17

Part III: Anisotropic metallic surface Purple Zone BRDF pattern versus wavelength BDRF is modulated by the interference fringes Yellow Zone BRDF measurements of Cu sample for incidence 30 along azimuth 0 Slide #18

Part III: Anisotropic metallic surface Standard Fourier plane is geometrically distorted (1) Normal Fourier Plane BRDF Fourier Plane XX = θθ RR ccccccφφ RR YY = θθ RR ssssssφφ RR XX = θθ NN ccccccφφ NN YY = θθ NN ssssssφφ NN (1) L. Simonot, G. Obein, Geometrical considerations in analyzing isotropic or anisotropic surface reflections, Applied Optics, Vol. 46, N 14, 2615 (2007) Slide #19

Part III: Anisotropic metallic surface Standard Fourier Space BDRF space emphasize the brushing direction BRDF Space BRDF measurements on purple zone of Cu sample for incidence 30 along azimuth 0 and wavelength 600nm Slide #20

Part III: Anisotropic metallic surface Purple Zone Interference fringes Modulate the BRDF patterns Yellow Zone BRDF measurements of Cu sample in the BRDF space for incidence 30 along azimuth 90 Slide #21

Part III: Anisotropic metallic surface 0.5 Ray emission lamp 0.4 Emission (a.u) 0.3 0.2 0.1 0 380 480 580 680 780 Wavelength (nm) 0.33 0.545 Color coordinates in the u v 1976 CIE system 0.32 0.31 u' 0.3 0.54 v' 0.535 0.29 Yellow Purple Yellow Purple 0.28 0 20 40 60 80 Incidence angle (deg) Color simulation of Cu sample using full diffused reflectance Slide #22 0.53 0 20 40 60 80 Incidence angle (deg)

Part III: LCD with variable top polarizer A demo LCD display with four different regions where the top polarizer has been replaced by a different polarizers films o Anti Glare 30 (AR30) o Anti Glare 380 (AR380) o Anti Glare Low Reflection (AGLR) o Anti Glare Anti Reflection (AGAR) Slide #23

Part III: LCD with variable top polarizer Intrinsic emissive properties AG30 AG380 Better contrast due to lower black state AGLR AGAR Luminance contrast for the four top polarizers Slide #24

Part III: LCD with variable top polarizer AG30 AG380 Much lower reflectance AGLR AGAR Full diffused spectral reflectance at 600nm for the 4 top polarizers Slide #25

Part III: LCD with variable top polarizer 500cd/m 2 Luminance contrast at normal incidence versus full diffused luminance for the four top polarizers: illuminant D65 Slide #26

Part III: LCD with variable top polarizer AG30 & AG380 comparable AG30 AG380 AGAR Best solution AGLR AGAR Luminance contrast with 500cd/m 2 full diffused illumination for the four top polarizers: isolevel = 10, illuminant D65 Slide #27

Part III: LCD with variable top polarizer AG30 AG380 Along horizontal azimuth AGLR AGAR BRDF measured at 600nm with collimated beam illumination at 25 for the four top polarizers: isolevel at 0.1, logarithmic scale Slide #28

Part III: LCD with variable top polarizer AG380 much glossier than AG30 BRDF measured at 600nm along horizontal azimuth with collimated beam illumination at 25 for the four top polarizers Slide #29

Part III: LCD with variable top polarizer AG380 & AG30 have now different performances Luminance contrast versus illuminance computed for the four top polarizers at specular position and 20 of incidence: Collimated beam illumination at 25, illuminant D65 Slide #30

Part III: OLED display Standard Fourier Space BRDF Space BRDF measured at 689nm on curved OLED TV for an incident beam 40 incidence and different azimuths Slide #31

Ray tracing simulations Slide #32

Part IV: Ray tracing simulations Proposal for integration in the Information Display Measurement Standard (ICDM) EXR file formats for saving all emissive or reflective properties of a display (www.openxr.com) Emissive viewing angle behavior is measured & stored as : Parts : Data input value (From 0 to 255) as Layers : R, G & B pixels Channels : Per X, Y & Z or per wavelength values versus angle Reflective BRDF behavior is measured & stored as Layers : Input angles Channels : Per wavelength output values versus angle Slide #33

Part IV: Ray tracing simulations Viewing angle emissive properties of a display in one file Slide #34

Part IV: Ray tracing simulations Ocean light simulator Floor illumination in building General purpose light simulation software Building with solar control coated glass Perfume bottles Car render based on measured paint and glass optical data See http://www.eclat-digital.com/ for details Slide #35

Part IV: Ray tracing simulations Software features for display simulation Available Emissive properties Use directly measured viewing angle properties Interpolation for any grey level value on each sub-pixel Simulation of any high resolution color image Capacity to introduce some in-homogeneities Reflective properties Use directly measured spectral BRDF properties Interpolation for any incidence angle for isotropic surfaces Interpolation for any incidence & azimuth angle for anisotropic surfaces (in-progress) Polarization properties (in the future) Use of measured polarization state of the light emitted by the display Use of polarization dependence of the spectral BRDF in progress Slide #36

Part IV: Ray tracing simulations Without reflection Simulation of Samsung curved LCD display Slide #37

Part IV: Ray tracing simulations With diffusing reflection properties 1000 100 Diffusing Glossy BRDF (str-1) 10 1 0.1 Simulation of Samsung curved LCD display 0.01 20 25 30 35 40 Angle (deg) BRDF at 30 and 550nm Slide #38

Part IV: Ray tracing simulations With glossy reflection properties 1000 100 Diffusing Glossy BRDF (str-1) 10 1 0.1 Simulation of Samsung curved LCD display 0.01 20 25 30 35 40 Angle (deg) BRDF at 30 and 550nm May 16 th, 2016 CORM Annual Technical Conference, Gaithersburg Slide #39

Conclusions Slide #40

Conclusions EZContrast-MS allows different types of multispectral measurement for the full viewing angle o o o Emissive properties : spectral radiance, color & luminance Spectral reflectance for full diffused illumination Spectral BRDF for collimated beam illumination Computations: o o o o Computation of luminance contrast under any illumination conditions Computation of color gamut under any illumination conditions Simultaneous full diffused and collimated illuminations possible Computations for all the illumination conditions found in standards possible! Physico-realistic rendering of any display possible o o Need to measure grey level dependence of intrinsic emission Reflective properties of any ambient lighting can be taken into account Slide #41

Thanks for your attention ELECTRONICS FOR DISPLAYS AND IMAGING DEVICES 1185, rue d EPRON 14200 Hérouville Saint-Clair France Phone : +33 2 31 94 76 00 Fax : +33 2 31 940 950 E-mail : eldim@eldim.fr Slide #42