Improvement of Visual Rendering

of Color and Texture

Fco M. Martínez-Verdú

Color & Vision Group: http://web.ua.es/en/gvc

University of Alicante (Spain)

verdu@ua.es

November 22nd, 2017, Paris, France

Supreme test of any visual rendering project: Simulated vs. real scenario: key elements for optimal success

Current challenges from gonio-apparent materials Multi-scale and hybrid approach

BRDF approach: models vs. empirical data & its PCA modeling

Ideal display technology for visual rendering Spatial resolution, HDR and color gamut

Progress from AKZNC-CSIC-UA collaboration

Conclusions

OUTLINE

3rd Annual Lighting Materials & Design Conference

Human Visual System (HVS) has evolved for survival

based on discrimination task;

Color & texture memory, or reproduction by preference, is

not accurate. This is the main advantage of visual rendering.

Visual validation of any rendering project: Haploscopic viewing of

rendered vs. real scenario

SUPREME TEST

3rd Annual Lighting Materials & Design Conference

Display technology features: Minimum pixel size: spatial resolution on screen (even projected)

HDR & sRGB color space model, or any derivation from them

Computational power continuously growing (bit depth, …) Local and integral control, both statically and dynamic

Complex mathematical models for materials implemented into

software

KEY ELEMENTS FOR SUCCESS

3rd Annual Lighting Materials & Design Conference

Color & Texture

Reflection & Transmission

Goniochromatism: BRDF

Sparkle & Graininess

GONIO-APPEARANCE OF MATERIALS

® Wikipedia

3rd Annual Lighting Materials & Design Conference

• Bottom – up:

• Many variables

• Impracticable

• Top – down:

• Feasible

• How?

CHALLENGES: MULTI-SCALE APPROACH

3rd Annual Lighting Materials & Design Conference

Color, Texture

Radiative

transfer theory

Particles

interaction

Light – Matter

interaction

particle models

Light sources tech.,

Pigments, dyes

Gloss, sparkle, etc.

Color differences

Visual appearance

Emission SPD(l)

Reflection r(l)

Transmission t(l)

Coefficients:

Absorption K

Scattering S

Substrate

Coloration

application

processes:

no. layers, etc.

Phys. + Chem.

Particles & Substrate:

Size, Shape, Thickness

Refraction index,

Extinction index,

Roughness, etc.

TH

EO

RE

TIC

AL

AP

PR

OA

CH

EX

PE

RIM

EN

TA

L A

PP

RO

AC

H

More examples

GONIO-APPEARANCE OF MATERIALS

3rd Annual Lighting Materials & Design Conference

More real examples

GONIO-APPEARANCE OF MATERIALS

3rd Annual Lighting Materials & Design Conference

Bi-Directional Reflectance Distribution Function (BRDF)

BDRF APPROACH

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direction of

illuminationGlossColor

Roughness

Artefacts

Texture

Sparkle

BRDF is a simplified BSSRDF

® Wikipedia

Theoretical vs. real models

BDRF MODELS

3rd Annual Lighting Materials & Design Conference

Gonio-spectrophometer (CSIC, Madrid) + PCA modeling

Principal Component Analysis (PCA)

400 measurement geometries

Flake – based parameters

OUR BRDF MODEL

3rd Annual Lighting Materials & Design Conference

θs

D(θflake)

θflake

θinc

θi

Rx(θinc,l)

Definition of θinc and θflake

Kirchner, E. and W. Cramer. 2012. Color Res. Appl. 37: 186-198.

PCA modeling results: dimensionality reduction

OUR BRDF MODEL

3rd Annual Lighting Materials & Design Conference

350 400 450 500 550 600 650 700 750 80010

-4

10-3

10-2

10-1

100

101

102

Wavelength/nm

BR

DF

/sr-

1

Lapis Sunligth

300 400 500 600 700 800-15

-10

-5

0

5

10

15

20

Wavelength/nm

A

Component #1: 90 % Component #2: 6.5 %

300 400 500 600 700 800-4

-2

0

2

4

6

Wavelength/nm

A

Component #3: 2.8 %

300 400 500 600 700 800-3

-2

-1

0

1

2

3

Wavelength/nm

A

Component #4: 0.6 %

300 400 500 600 700 800-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

Wavelength/nm

A

Math fingerprint

𝐵𝑅𝐷𝐹 𝜆, 𝑒𝑡𝑐. =

𝑖=1

4

𝑒𝑖 𝑒𝑡𝑐. · 𝐴𝑖 𝜆

PCA potential: spectral BRDF prediction for any geometry

A = H (eigenspectra)

OUR BRDF MODEL

3rd Annual Lighting Materials & Design Conference

θhigh

θhigh

θlow

θlow

θxθx

Rlow(l)

Rhigh(l)

Rx(θx,l)?

?

?

PCA + flake-based parameter BRDF model: performance

OUR BRDF MODEL

3rd Annual Lighting Materials & Design Conference

Increasing spatial resolution (pixel reduction) never will be enough

The same for the HDR, i.e., Lwhite vs. Lblack en cd/m2 (> 105)

And, even with this, the next frontier will be to use multi-primary

displays to reproduce faithfully gonio-apparent materials

OLED, QD, etc.?

IDEAL DISPLAY TECH. FOR RENDERING

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Main purpose: visual validation of color & sparkle rendering

spectral BRDF data measured from Madrid: PCA modeling + isoline concept

color calibration of advanced displays (LCD, OLED, and QD)

evaluation of color reproduction of some gonio-apparent samples

AZKNC – CSIC – UA COLLABORATION

3rd Annual Lighting Materials & Design Conference

Merck Colorstream® under:Philips QDsRGB

Main purpose: visual validation of color & sparkle rendering using a

directional lighting booth and calibrated display of plane gonio-

apparent samples

Blender implementation of the byko-spectra effect cabinet

Real lighting set-up and environment into cabinet from the observer viewing position

Psychophysical test (Likert 5-scaling) for many observers (firstly, by diffuse

lighting)

AZKNC – CSIC – UA COLLABORATION

3rd Annual Lighting Materials & Design Conference

Score Description

0 No / Hardly any difference

1 Small, negligible difference

2 Difference visible but still acceptable

3 Difference visible, doubtful match

4 Difference clearly visible, not correct match

5 Large difference, very bad match

Visual validation of color & sparkle rendering using a directional

lighting booth and calibrated display of plane gonio-apparent

samples

AZKNC – CSIC – UA COLLABORATION

3rd Annual Lighting Materials & Design Conference

Visual rendering has still an are of improvement for increasing of

the optimal photorealistic reproduction of visual appearance of

gonio-apparent materials combining multi-scale hybrid knowledge

from science, engineering and design.

Computational power, with new advances in display technologies

(HDR, QD, etc.), even in multi-primary approach, can be provided

interesting and feasible solutions at short term.

CONCLUSIONS

3rd Annual Lighting Materials & Design Conference

This research initiative is indirectly supported by the European Union and

Spanish Ministry of Economy and Competitiveness under the grant DPI2015-

65814-R with European Regional Development Funds (ERDF) support.

This research is also done within the EMRP 16NRM08 Project

BiRD “Bidirectional Reflectance Definitions”.

The EMPIR initiative is jointly funded by the EMRP

participating countries within EURAMET

and the European Union.

ACKNOWLEDGEMENTS

3rd Annual Lighting Materials & Design Conference

ACKNOWLEDGEMENTS

3rd Annual Lighting Materials & Design Conference

Ferrero, A., et al. (2013): “Spectral BRDF-based determination of proper geometries to

characterize color shift of special effect coatings”. JOSA A, 30(2), 206-214.

Ferrero, A., et al. (2015): “Global color estimation of special-effect coatings from measurements

by commercially available portable multiangle spectrophotometers”. JOSA A, 32(1), 1-11.

Kirchner, E., et al. (2015): “Fast and accurate 3D Rendering of automotive coatings”. Color

Imaging Conference, 23, 154-160.

Kirchner, E., et al. (2017): “Improving color reproduction accuracy of a mobile liquid crystal

display”. JOSA A, 34(1), 101-110.

Kirchner, E., et al. (2017): “Improving color reproduction accuracy of a OLED-based display”.

Color Res. Appl. (accepted, on press: 10.1002/col.22148).

Huraibat, K., et al. (2017): “Spectral and color characterization of a quantum dots display for

gonio-apparent colors”. Color Imaging Conference, 25, 177-181.

REFERENCES

3rd Annual Lighting Materials & Design Conference

Improvement of Visual Rendering

of Color and Texture

Fco M. Martínez-Verdú

Color & Vision Group: http://web.ua.es/en/gvc

University of Alicante (Spain)

verdu@ua.es

November 22nd, 2017, Paris, France