An Evaluation of the Current State of Digital Photography Charles Dickinson Advisor: Jeff Pelz

Main Objective n Gain a better understanding of the state of digital photography

Overview n Introduction n Experimental n Results n Conclusions n Review

Introduction n Goal: Evaluate digital photography from digital camera input to printer output n Metrics: MTF and subjective evaluation

Questions to be Answered n Obtain a model for digital photography n What is gained by upgrading a camera / printer in a digital photographic system? n What are the effects of interline vs. frame transfer?

Experimental n Kodak DC120, DC260, DCS315, DCS460 n Epson Stylus 800, Kodak 8670 n Photoshop, IDL, Image Analyzer, Imlab

Digital Camera Characterization n Adopted slanted knife edge method n Software: PIMA Image Analyzer plug-in, ISO 12233

Image Analyzer n Calculates MTF given a slanted knife edge n Easy to use, robust edge angle, predicts MTF up to 4 times Nyquist frequency 1 1.)Benchmarking of the ISO Slanted-edge Spatial Frequency Response Plug-in, Don William, IS&T’s 1998 PICS Conference, pp )Benchmarking of the ISO Slanted-edge Spatial Frequency Response Plug-in, Don William, IS&T’s 1998 PICS Conference, pp

Procedure n Image target in upright position n Convert image to Lab space and remove a and b channels in Photoshop n IDL program takes rectangle within reflectance targets and averages values (Digital Count, dc)

Target Image (DC260)

Procedure n Input dc values into Excel, plot vs. known reflectances n Fit trendline and calculate reflectances for 256 dc’s n In Photoshop, select ROI, use Image analyzer ‘filter’ n Image analyzer calls for ‘OECF’

Printer Characterization n IDL creates sine patterns, print in Photoshop n Examine under microdensitometer with Imlab n Determine MTF with histogram of sine pattern

Sine Histograms Reflectance # pixels idealreal Reflectance max max min min Modulation = (Rmax - Rmin) / (Rmax + Rmin)

Subjective Evaluation n Four questions: sharpness, color preference, color reproduction, overall quality n 1-10 rating n Image with DC120 and DCS460 printed on dye-sub and inkjet, traditional photograph n 5 x 7 inch prints

Subjective Image

Camera Results

Camera Discussion n DCS460 performs best, DC120 worst n DC260 has edge enhancement n DCS315 performed worse than DC260

Printer Results

Printer Discussion n Inkjet performs better than dye-sub n Due to binary nature of inkjet

Subjective Results: Overall

Subjective Results: Sharpness

Subjective Results: Color Preference

Subjective Results: Color Reproduction

Subjective Results Discussion n DCS460, inkjet combination did the best for sharpness, color, but 460, dye-sub system did better overall n Photograph didn’t perform best in any category n For DC120, inkjet and dye-sub perform about the same

System Results

System Results Discussion n DC260/inkjet system performed the best n For DC120, DCS315: printer makes small change in MTF n For DC260, DCS460: printer makes large change in MTF

Conclusions n Interline vs. frame transfer comparison can’t be done with DC260, DCS315 n For low end camera, printer upgrade is insignificant to MTF n High end camera MTFs benefit from printer upgrade n Although inkjet has better MTF, dye-sub is more pleasing to eye

Review n Gain model for digital photographic systems n Accomplished, but: – MTF doesn’t completely describe system – Subjective evaluations for DC120, DCS460 only

Special Thanks Dr. Jeff Pelz Dr. Jeff Pelz Dr. John Arney Dr. John Arney