Fast Spectral Reflectance & BRDF Measurements of ...

October 7-9, 2014 Le Westin Montreal, Canada

Fast Spectral Reflectance & BRDF Measurements of Cosmetic Foundations and their Components P. BOHER*, T. LEROUX*, L. CAVÉ*, L. BLAIN**, V. BOULIER**, (*) ELDIM, 1185 rue d’Epron, 14200 Hérouville St Clair, France (**) SENSIENT COSMETIC Technologies, 7-9 rue de l'industrie, 95310 Saint Ouen l'Aumône, France

Pigment & Color Science Forum

Slide #1

Agenda

I.

Introduction

II. ELDIM Multispectral viewing angle instrument 1.

Optical Setup

2.

Reflective toolkit

3.

Spectral reflection & spectral BRDF

III. Experimental results 1.

Diffusion powders

2.

Foundations creams

IV. Computations 1.

Color of foundation creams under various illuminations

V. Conclusions


Slide #2

Part I: Introduction Appearance of human skin with or without cosmetic foundation is generally judged by eyes. Even if in human color vision, the transformation of reflected light from the spectra to trichromatic signals results in the loss of most of the spectral features, the knowledge of the spectral reflectance of this type of object is much more informative than a simple color analysis. Moreover, the diffusion properties and their spectral and angular dependence are key parameters to understand the different aspects (color, glossiness, luminosity...) of a complex object such as a human face. In addition the spectral dependence allows prediction of the aspect of any surface under any type of illumination.


Slide #3

Part I: Introduction Most general means to characterize the reflection properties of a surface is by use of the bi-directional reflection distribution function (BRDF). The BRDF of a surface is the ratio of reflected radiance to incident irradiance at a particular wavelength: 𝑑𝐿𝑟 (𝜃𝑖 , 𝜃𝑟 , 𝜑𝑟 , 𝜆) 𝐵𝐵𝐵𝐵(𝜃𝑖 , 𝜃𝑟 , 𝜑𝑟 , 𝜆) = 𝑑𝐸𝑖 (𝜃𝑖 , 𝜆)

For one isotropic surface 4 different parameters:    

Incidence angle ϴi Reflection angle ϴr Reflection angle φi Wavelength λ Light reflection geometry Pigment & Color Science Forum

Slide #4

Part I: Introduction Traditionally, BRDF measurements were taken for a specific lighting and viewing direction at a time using conventional goniometer. Unfortunately, using such a device to densely measure the BRDF is very time consuming.


Slide #5

Part I: Introduction The purpose of the present talk is to introduce the use of Fourier optics instruments to measure spectral BRDF within reasonable measurement times. ELDIM has introduced the use of Fourier optics instrument for the characterization of the viewing angle of displays in 1993. The principle is based on an optical Fourier transform (OFT): a specific optic is designed in order to convert angular field map into a planar one. This Fourier plane is reimaged by a CCD detector in order to measure all the angles simultaneously


Slide #6

Part II: Measurement technique

EZContrast XL88MS features:  Angular aperture ±88°  Spot size up to 2mm  31 wavelengths from 400 to 700nm  Polarization analysis at each λ


Slide #7

Part II: Measurement technique Fourier Plane

Field Lens

Polarizers & Waveplates

display

Array Sensor

Iris Relay Lens Polarizer filter

Band pass filters

Fourier Lens

Angular aperture & spot size are controlled independently Multispectral measurement is made with 31 band pass filters Pigment & Color Science Forum

Slide #8

Part II: Measurement technique 70.00

60.00

Transmittance (%)

50.00

40.00

30.00

20.00

10.00

0.00 350

400

450

500

550 Wavelength (nm)

600

650

700

750

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 band-pass width 3. Luminance and color can be computed Pigment & Color Science Forum

Slide #9


Fourier optics

Full Fourier Field lens plane

Field iris Beam Splitter Fourier plane

Sample CCD Imaging lens illumination lens Illumination Fourier plane

Beam splitter and additional optics are used for illumination: Integration sphere for full diffused illumination Optical fiber for collimated beam illumination Pigment & Color Science Forum

Slide #10


CCD camera Band pass filters Optical fiber Additional optics Fourier optics Sample

Power supply Xenon lamp


Slide #11


Common specifications Field

Incidence angle Azimuth angle

Measuring area

Maximum diameter

Working distance Spectral specs Measurement time

Full resolution Half resolution

Accuracy

Wave resolution (nm) Angle resolution (deg) Radiance (W/Str/m2/nm) Chromaticity error

EZContrast MS88

EZContrast MS80

EZLiteN

±88° 0-360°

±80° 0-360°

±60° 0-360°

2mm

2mm

2mm

1mm

3.7mm

4.5mm

10nm 31 band pass filters

20nm 16 filters

< 6mn