Ph.D. Course in Digital Halftoning

Ph.D. Course in Ph.D. Course in

Digital HalftoningDigital Halftoning

Examples of Colorimetric Modeling Examples of Colorimetric Modeling MethodsMethods

Lars Bergman, Halmstad UniversityLars Bergman, Halmstad University

23-04-2223-04-22 Digital halftoning - Lars BergmanDigital halftoning - Lars Bergman 22

PapersPapers

A Critical Review of Spectral Models A Critical Review of Spectral Models Applied to Binary Color Printing Applied to Binary Color Printing

The Spectral Modeling of Large Format The Spectral Modeling of Large Format InkJet Printers InkJet Printers


ForwardForward RGB -> CMY(K)RGB -> CMY(K)

ReversedReversed How much CMY(K) for a given RGBHow much CMY(K) for a given RGB

– Predict the spectral output of the printerPredict the spectral output of the printer– Effective dot areaEffective dot area


Effective dot areaEffective dot area

Mechanical dot gainMechanical dot gain– Ink cover larger area on paper then Ink cover larger area on paper then

intendedintended Optical dot gainOptical dot gain

– Light spread in paper (and ink)Light spread in paper (and ink)


Typical machanical dot gain Typical machanical dot gain

for a desktop inkjet printerfor a desktop inkjet printer

A Critical Review of Spectral A Critical Review of Spectral Models Applied to Binary Models Applied to Binary Color PrintingColor Printing


ModelsModels

Regression basedRegression based Murray-Davis Neugebauer Yule-Nielsen Yule-Nielsen

modified Neugebauer

Cellular Neugebauer Yule-Nielsen with

spectral depending N-value

First principals modelsFirst principals models (Regressing the

Neugebauer Primarys)

(Expanded Murray-Davis Model)

The Propability model

Modeling paper spread function


Murray-DavisMurray-Davis


effective areaeffective area


NeugebauerNeugebauer



Yule-Nielsen

Trys to correct for the non linearity in Trys to correct for the non linearity in Murray-Davis modelMurray-Davis model

Recomended N=1.7 for offset printsRecomended N=1.7 for offset prints



Yule-Nielsen modified Neugebauer Combining Yule-Combining Yule-

Nielsen and Nielsen and NeugebauerNeugebauer

Yule-Nielsen is used Yule-Nielsen is used separate for each separate for each colorcolor


Cellular Neugebauer


Yule-Nielsen with spectral depending N-value

Spectral reflectance for primary

cyan ramp


The Propability model

Light path ProbabilitiesLight path Probabilities



Modeling paper spread function Convolution with LP filterConvolution with LP filter Can handle nonuniform Can handle nonuniform

screens/dotsscreens/dots Computational heavyComputational heavy


Quality meassure Quality meassure

Spectral fitnessSpectral fitness RMS Spectral errorRMS Spectral error

Tristimulus fitness Tristimulus fitness – Humanly correctHumanly correct– ICC profilesICC profiles

CIE CIE EE


Model performancesModel performances

The Spectral Modeling of The Spectral Modeling of Large Format InkJet Large Format InkJet Printers Printers


ScreeningScreening

Determing the number of colors (ink Determing the number of colors (ink combinations)combinations)


HP650CHP650C

HP650 use ”Scatter mode”

FM-based screening


TestdataTestdata

Primary ramp

CMYRGBK Ramp

Test target used to

characterize each color types

spectral absorptivity.


Meassured spectral rflectance

factor data of a cyan ramp


Linear model prediction for

50% cyan using Murray-Davis

model


Normalized reflectance factor

spectra for cyan ramp data




using Yule-Nielsen-model

N=1.7




using Yule-Nielsen-model

N=10


Linear model prediction for

50% cyan


Normalized absorbtion spectra

for cyan ramp data using

Kubelka-Munck transparent

model


Normalized absorptivities

based on eigenvector

analyses of eight possible

color types.


MethodMethod

1. Evaluate halftoning algorithm in order to determine the number of possible colortypes.

2. Hypothesize a color formation model3. Evaluate how well the hypothesized model

predict primary ramps4. Evaluate secondary and tertiaries ramps5. Quantify the mechanical dot gain


ExperimentsExperiments

Device driverDevice driver GCRGCR RegistrationRegistration Test target designTest target design Printer stabilityPrinter stability


Optimized Yule-Nielsen n value for CMYRGBK

The ENDThe END

Documents

Ph.D. Course in Digital Halftoning