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An Evaluation of the Current State of Digital Photography

An Evaluation of the Current State of Digital Photography Charles Dickinson Advisor: Jeff Pelz Main Objective Gain a better understanding of the state of digital photography Overview Introduction Experimental Results Conclusions Review Introduction

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An Evaluation of the Current State of Digital Photography

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

  2. Main Objective • Gain a better understanding of the state of digital photography

  3. Overview • Introduction • Experimental • Results • Conclusions • Review

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

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

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

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

  8. Image Analyzer • Calculates MTF given a slanted knife edge • Easy to use, robust edge angle, predicts MTF up to 4 times Nyquist frequency1 • 1.)Benchmarking of the ISO 12233 Slanted-edge Spatial Frequency Response Plug-in, Don William, IS&T’s 1998 PICS Conference, pp 133-136

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

  10. Target Image (DC260)

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

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

  13. Sine Histograms ideal real # pixels # pixels min max max min Reflectance Reflectance Modulation = (Rmax - Rmin) / (Rmax + Rmin)

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

  15. Subjective Image

  16. Camera Results

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

  18. Printer Results

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

  20. Subjective Results: Overall

  21. Subjective Results:Sharpness

  22. Subjective Results: Color Preference

  23. Subjective Results: Color Reproduction

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

  25. System Results

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

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

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

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

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