An image based multi-angle measurementsetup

Aditya Sole

The Norwegian Colour and Visual Computing Laboratory, Norwegian University of Science and Technology

Gjøvik, Norwayaditya.sole@ntnu.no

http://www.ntnu.edu/colourlab

29th June, 2017

ICC Graphic Arts Experts’ Day, The Czech Academy of Sciences in Prague, June 29, 2017

1

Introduction

Appearanceofanobjectmaterial

sparadvertising.com

www.beautypackaging.co

m

WhatColor?Glossy/matte?Texture?Opaque/translucent?

MaterialAppearance

2

Introduction

Appearanceofanobjectmaterial

sparadvertising.com

www.beautypackaging.co

m

WhatColor?Glossy/matte?Texture?Opaque/translucent?

MaterialAppearance

Objectivedescription

Surfacereflectance,Specularmeasurement,texturepatterns,Opacity,etc.

PhysicalMeasurements

3

4

Non-diffuse, gonio-chromatic materials

www.scrangie.com

• Usedinpackagingindustry,carpaintindustry,banknotesetc.• Createdusing,

• Metallicinks,• Pearlescent,varnishcoatings,• Specialeffectpigments,• Holographicfoils.

• Producedesirableappearancebyshift/changeinperceivedcolour dependinguponillumination/viewinggeometry.

• Changeduetovaryingreflectionatdifferentviewingangles(basedonmaterialproperties).

5

• Multi-anglemeasurementinstrumentsavailableinthemarket,

• X-RiteMA98,BYC-MAC,etc,• Gonio-reflectometers atmetrology

institutes.

GONIO-MEASUREMENTS / MULTI-ANGLE MEASUREMENTS

Images taken from:K. Kehren, Optical Properties and Visual Appearance of Printed Special Effect Colors, PhD thesis, Technischen Universität Darmstadt, Darmstadt, Germany, April 2013.

Licensed under CC BY-NC-ND

Limitations:• Measurementsaretimeconsuming

(especiallyGonio-reflectometers),• Expensive.

6

Motivation

• Canweperformmulti-anglemeasurementsinafastandrelativelyin-expensiveway?

• Canthemeasurementsbedoneonlineduringthereproductionand/orimagequalityevaluationproceduresintheproductionline?

7

Image based multi-angle measurement setup1,2

• Animage-basedmulti-anglemethodformeasurementofhomogeneousflexibleobjectmaterial

• UsingpointlightsourceandaRGBcamera,

• Estimatetheincident(θi) andreflection(θr) anglesofacurvedsample.

cosθi =PL ⋅nPL

cosθr =PC ⋅nPC

dL

(dC))(

d

θLθS

θiθr (n)(P)

Camera

Light source

1. A.Sole;I.Farup;S.Tominaga,“Animage-basedmulti-directionalreflectancemeasurementsetupforflexibleobjects”,Proc.SPIE9398,Measuring,Modeling,andReproductionMaterialAppearance2015,93980J(March13,2015)

2. A.Sole,IFarup,STominaga,(2014)Animagebasedmulti-anglemethodforestimatingreflectiongeometriesofflexibleobjects,Proc.IS&T/SID22ndColorImagingConference,Boston,Arizona,USA,91-96.

8

Image based multi-angle measurement setup1,2

dL

(dC))(

d

θLθS

θiθr (n)(P)

Camera

Light source

1. A.Sole;I.Farup;S.Tominaga,“Animage-basedmulti-directionalreflectancemeasurementsetupforflexibleobjects”,Proc.SPIE9398,Measuring,Modeling,andReproductionMaterialAppearance2015,93980J(March13,2015)

2. A.Sole,IFarup,STominaga,(2014)Animagebasedmulti-anglemethodforestimatingreflectiongeometriesofflexibleobjects,Proc.IS&T/SID22ndColorImagingConference,Boston,Arizona,USA,91-96.

9

Image based multi-angle measurement setup1,2

dL

(dC))(

d

θLθS

θi

θr(n)(P)Camera

Light source

1. A.Sole;I.Farup;S.Tominaga,“Animage-basedmulti-directionalreflectancemeasurementsetupforflexibleobjects”,Proc.SPIE9398,Measuring,Modeling,andReproductionMaterialAppearance2015,93980J(March13,2015)

2. A.Sole,IFarup,STominaga,(2014)Animagebasedmulti-anglemethodforestimatingreflectiongeometriesofflexibleobjects,Proc.IS&T/SID22ndColorImagingConference,Boston,Arizona,USA,91-96.

10

Image based multi-angle measurement setup1,2

dL

(dC))(

d

θL θS

θi

θr

(n)

(P)

Camera

Light source

1. A.Sole;I.Farup;S.Tominaga,“Animage-basedmulti-directionalreflectancemeasurementsetupforflexibleobjects”,Proc.SPIE9398,Measuring,Modeling,andReproductionMaterialAppearance2015,93980J(March13,2015)

2. A.Sole,IFarup,STominaga,(2014)Animagebasedmulti-anglemethodforestimatingreflectiongeometriesofflexibleobjects,Proc.IS&T/SID22ndColorImagingConference,Boston,Arizona,USA,91-96.

11

Sample measurement• Assumingmeasurementsample

tobehomogeneousandopaquewemeasurewith:

• 10illuminationdirections,• Spectralon tileasreference

tiletoestimatelinearRGBcameraresponseoftheincidentlight,

• NikonD200DSLRcamera,• Tungstenpointlightsource,• Printedpackagingsheetas

sample

A.Sole,I.Farup,andP.Nussbaum,“Evaluatinganimagebasedmulti-anglemeasurementsetupusingdifferentreflectionmodels”,inMaterialAppearance,vol.2017,no.8,pp.101-107,ProceedingsIS&TElectronicImaging,2017

Munsell White

Red

Cyan

Pantone 10309C

Magenta

Pantone 10213C

Pantone 10153C

Spectralon tile

12

Surface reflectance using a reflection model• Forexample:

• Phong reflectionPhong reflectionmodelisanempiricalmodelwithtwosurfacereflectioncomponents,diffusereflectionofroughsurfacesandspecularreflectionofshinysurfaces

• Cook-TorrancemodelCTmodelisaphysicalmodelthatdescribestheintensityandspectralcompositionofthelightreflectedfromtheobject/material.

• IsotropicWardmodelWardmodelisaphenomenologicalmodeldevelopedwiththeaimtofitmeasuredreflectancedatawithasimpleempiricalformula.Itrepresentsbothisotropicandanisotropicreflectionand usesagaussian distributionforthespecularpeaks.

Comparing with Gonio/Multiangle spectrophotometers

Image taken from:K. Kehren, Optical Properties and Visual Appearance of Printed Special Effect Colors, PhD thesis, Technischen Universität Darmstadt, Darmstadt, Germany, April 2013.

Licensed under CC BY-NC-ND

CameraSetup– RGB Multi-angle/GoniospectrophotometerSetup– Spectral400– 700nm

Image taken from:http://www.ebay.com/gds/Nikon-D200-Vs-Nikon-D-Series-D300-

/10000000177709780/g.html

13

CameraMeasurement

RGB

Multi-angle/Goniospectrophotometer

Spectralreflectance400nm........700nm

XYZ=XYZreflectance,RGB=Illuminantindependentcameraresponseofthesamplematerial,

XYZ

𝑋 =#𝐶𝑟 𝜆 𝑅𝑒(𝜆)+,,

-,,

𝑌 =#𝐶𝑔 𝜆 𝑅𝑒(𝜆)+,,

-,,

𝑍 =#𝐶𝑏 𝜆 𝑅𝑒(𝜆)+,,

-,,

XYZRe(𝜆)=spectralreflectance,𝑪3(𝑪𝒓 𝝀 𝑪𝒈 𝝀 𝑪𝒃 𝝀 )=transformedcolour matchingfunctionsusingcamerasensitivityfunctionsand2○ (�̅�,𝑦<,𝑧̅)colour matchingfunctions.

∎ ∎ ∎∎ ∎ ∎∎ ∎ ∎

14

Comparing with Gonio-spectrophotometers

𝑀3

Transformation Matrix (𝑀3) and transformed colourmatching functions (𝐶@)

𝑀3 = 𝑎𝑟𝑔minE

𝐶 − 𝑅𝑀 G

C=31x3matrix(CIE2○ colour matchingfunctions),

R=31x3matrix(camerasensitivityfunctions(𝑟 𝜆 , 𝑔(𝜆),b(𝜆)),

𝑀3=3x3transformationmatrix,

𝐶@=31x3matrix(transformedcolour matchingfunctions),

𝐶@ = 𝑅𝑀3

15

A.Sole,I.Farup,andS.Tominaga,“Imagebasedreflectancemeasurementbasedoncameraspectralsensitivities,”inMeasuring,ModelingandReproducingMaterialAppearance2016(M.V.O.Segovia,P.Urban,andF.H.Imai,eds.),vol.2016,no.9,pp.1– 8,Proceedings IS&TElectronicImaging,2016.

XYZ_Y value of Cyan sample

16

Munsell White

Red

Cyan

Pantone 10309C

Magenta

Pantone 10213C

Pantone 10153C

Spectralon tile

Sample

A.Sole,I.Farup,andP.Nussbaum,“Evaluatinganimagebasedmulti-anglemeasurementsetupusingdifferentreflectionmodels”,inMaterialAppearance,vol.2017,no.8,pp.101-107,ProceedingsIS&TElectronicImaging,2017

17

• Measurement data divided into training and test data set

• Training set: 5°, 15°, 20°, 25°

and 30°

• Training of Cook-Torrance and Isotropic Ward model

Training of the reflection models

A.Sole,I.Farup,andP.Nussbaum,“Evaluatinganimagebasedmulti-anglemeasurementsetupusingdifferentreflectionmodels”,inMaterialAppearance,vol.2017,no.8,pp.101-107,ProceedingsIS&TElectronicImaging,2017

18

Cyan sample𝐻𝑖𝑠𝑡𝑜𝑔𝑟𝑎𝑚𝐶𝑦𝑎𝑛𝑆𝑎𝑚𝑝𝑙𝑒𝐶𝑇𝑎𝑛𝑑𝑊𝑎𝑟𝑑𝑚𝑜𝑑𝑒𝑙

ResultMunsell White

Red

Cyan

Pantone 10309C

Magenta

Pantone 10213C

Pantone 10153C

Spectralon tile

• CYANsamplemeasuredusingtele-spectro-radiometerØ 𝐼𝑛𝑐𝑖𝑑𝑒𝑛𝑡𝑑𝑖𝑟𝑒𝑐𝑡𝑖𝑜𝑛(𝜃Y) = 40°, 𝑉𝑖𝑒𝑤𝑖𝑛𝑔𝑑𝑖𝑟𝑒𝑐𝑡𝑖𝑜𝑛𝑠(𝜃_) = −10°, 0°, 10°, 𝑎𝑛𝑑30°

• TrainedCTandWardmodelsusedtoestimatetheCIEYvalueatthesesameincidentandviewingdirections

Physical measurements using radiometer

CYANsample

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• For the sample materials used in this paper

Ø Satisfactory performance of both the reflections models for the given set of sample materials

Ø Directionalreflectionpropertiesofthematerialcanbeestimateddirectlyinthecolorimetricspace,

Ø Ward model estimates CIE Y values well for the measurements made with the tele-spectro-radiometer

20

Conclusion

21

Future work

• To evaluate the setup, perform sample measurements with the setup and compare with gonio-spectrophotometer measurements.

• Implement the method on highly specular and gonio-chromatic samples.

• Use the setup to measure specular materials along with more complex BRDF reflection models.

Thank you foryour attention

Contact information:AdityaS.SoleE-mail:aditya.sole@ntnu.noWeb:www.ntnu.edu/colourlab

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IlluminationandViewingangles