An Evaluation of the An Evaluation of the Current State of Current State of

Digital PhotographyDigital Photography

Charles Dickinson Charles Dickinson

Advisor: Jeff PelzAdvisor: Jeff Pelz

Main ObjectiveMain Objective

Gain a better Gain a better understanding of the state understanding of the state of digital photographyof digital photography

OverviewOverview

IntroductionIntroduction ExperimentalExperimental ResultsResults ConclusionsConclusions ReviewReview

IntroductionIntroduction

GoalGoal: Evaluate digital : Evaluate digital photography from digital photography from digital camera input to printer camera input to printer outputoutput

MetricsMetrics: MTF and subjective : MTF and subjective evaluationevaluation

Questions to be Questions to be AnsweredAnswered

Obtain a model for digital Obtain a model for digital photographyphotography

What is gained by upgrading a What is gained by upgrading a camera / printer in a digital camera / printer in a digital photographic system?photographic system?

What are the effects of interline What are the effects of interline vs. frame transfer?vs. frame transfer?

ExperimentalExperimental

Kodak DC120, DC260, Kodak DC120, DC260, DCS315, DCS460DCS315, DCS460

Epson Stylus 800, Kodak 8670Epson Stylus 800, Kodak 8670 Photoshop, IDL, Image Photoshop, IDL, Image

Analyzer, ImlabAnalyzer, Imlab

Digital Camera Digital Camera CharacterizationCharacterization

Adopted slanted knife edge Adopted slanted knife edge methodmethod

Software: PIMA Image Analyzer Software: PIMA Image Analyzer plug-in, ISO 12233plug-in, ISO 12233

Image AnalyzerImage Analyzer

Calculates MTF given a slanted Calculates MTF given a slanted knife edgeknife edge

Easy to use, robust edge angle, Easy to use, robust edge angle, predicts MTF up to 4 times Nyquist predicts MTF up to 4 times Nyquist frequencyfrequency11

1.)1.)Benchmarking of the ISO 12233 Slanted-edge Spatial Frequency Response Plug-inBenchmarking of the ISO 12233 Slanted-edge Spatial Frequency Response Plug-in , Don , Don

William, IS&T’s 1998 PICS Conference, pp 133-136William, IS&T’s 1998 PICS Conference, pp 133-136

ProcedureProcedure

Image target in upright positionImage target in upright position Convert image to Lab space and Convert image to Lab space and

remove a and b channels in remove a and b channels in PhotoshopPhotoshop

IDL program takes rectangle within IDL program takes rectangle within reflectance targets and averages reflectance targets and averages values (Digital Count, dc)values (Digital Count, dc)

Target Image (DC260)Target Image (DC260)

ProcedureProcedure

Input dc values into Excel, plot vs. Input dc values into Excel, plot vs. known reflectancesknown reflectances

Fit trendline and calculate Fit trendline and calculate reflectances for 256 dc’sreflectances for 256 dc’s

In Photoshop, select ROI, use In Photoshop, select ROI, use Image analyzer ‘filter’Image analyzer ‘filter’

Image analyzer calls for ‘OECF’Image analyzer calls for ‘OECF’

Printer CharacterizationPrinter Characterization

IDL creates sine patterns, print IDL creates sine patterns, print in Photoshopin Photoshop

Examine under Examine under microdensitometer with Imlabmicrodensitometer with Imlab

Determine MTF with histogram Determine MTF with histogram of sine patternof sine pattern

Sine HistogramsSine Histograms

ReflectanceReflectance

# pixels# pixels

idealideal realreal

ReflectanceReflectance

# pixels# pixelsmaxmax maxmaxminmin minmin

Modulation = (Rmax - Rmin) / (Rmax + Rmin)Modulation = (Rmax - Rmin) / (Rmax + Rmin)

Subjective EvaluationSubjective Evaluation

Four questions: sharpness, color Four questions: sharpness, color preference, color reproduction, overall preference, color reproduction, overall qualityquality

1-10 rating1-10 rating Image with DC120 and DCS460 printed Image with DC120 and DCS460 printed

on dye-sub and inkjet, traditional on dye-sub and inkjet, traditional photographphotograph

5 x 7 inch prints5 x 7 inch prints

Subjective ImageSubjective Image

Camera ResultsCamera Results

Camera DiscussionCamera Discussion

DCS460 performs best, DC120 DCS460 performs best, DC120 worstworst

DC260 has edge enhancementDC260 has edge enhancement DCS315 performed worse than DCS315 performed worse than

DC260DC260

Printer ResultsPrinter Results

Printer DiscussionPrinter Discussion Inkjet performs better than dye-subInkjet performs better than dye-sub Due to binary nature of inkjetDue to binary nature of inkjet

Subjective ResultsSubjective Results:: Overall Overall

Subjective ResultsSubjective Results::SharpnessSharpness

Subjective ResultsSubjective Results: : Color Color PreferencePreference

Subjective ResultsSubjective Results:: Color Color ReproductionReproduction

Subjective Results Subjective Results DiscussionDiscussion

DCS460, inkjet combination did the DCS460, inkjet combination did the best for sharpness, color, but 460, best for sharpness, color, but 460, dye-sub system did better overalldye-sub system did better overall

Photograph didn’t perform best in Photograph didn’t perform best in any categoryany category

For DC120, inkjet and dye-sub For DC120, inkjet and dye-sub perform about the sameperform about the same

System ResultsSystem Results

System Results System Results DiscussionDiscussion

DC260/inkjet system performed DC260/inkjet system performed the bestthe best

For DC120, DCS315: printer For DC120, DCS315: printer makes small change in MTFmakes small change in MTF

For DC260, DCS460: printer For DC260, DCS460: printer makes large change in MTFmakes large change in MTF

ConclusionsConclusions Interline vs. frame transfer comparison Interline vs. frame transfer comparison

can’t be done with DC260, DCS315can’t be done with DC260, DCS315 For low end camera, printer upgrade is For low end camera, printer upgrade is

insignificant to MTFinsignificant to MTF High end camera MTFs benefit from High end camera MTFs benefit from

printer upgradeprinter upgrade Although inkjet has better MTF, dye-sub Although inkjet has better MTF, dye-sub

is more pleasing to eyeis more pleasing to eye

ReviewReview

Gain model for digital photographic Gain model for digital photographic systemssystems

Accomplished, but:Accomplished, but:– MTF doesn’t completely describe MTF doesn’t completely describe

systemsystem

– Subjective evaluations for DC120, Subjective evaluations for DC120, DCS460 onlyDCS460 only

Special ThanksSpecial Thanks

Dr. Jeff Pelz Dr. Jeff Pelz

Dr. John ArneyDr. John Arney