An Evaluation of the Current State of Digital Photography

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

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Digital Camera Characterization

• Adopted slanted knife edge method
• Software PIMA Image Analyzer plug-in, ISO 12233

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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,
  ISTs 1998 PICS Conference, pp 133-136

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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)

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Target Image (DC260)
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Procedure

• Input dc values into Excel, plot vs. known
  reflectances
• Fit trendline and calculate reflectances for 256
  dcs
• 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

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Sine Histograms
ideal
real
pixels
pixels
max
min
max
min
Reflectance
Reflectance
Modulation (Rmax - Rmin) / (Rmax Rmin)
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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

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Subjective Image
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Camera Results
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Camera Discussion

• DCS460 performs best, DC120 worst
• DC260 has edge enhancement
• DCS315 performed worse than DC260

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Printer Results
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Printer Discussion

• Inkjet performs better than dye-sub
• Due to binary nature of inkjet

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Subjective Results Overall
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Subjective ResultsSharpness
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Subjective Results Color Preference
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Subjective Results Color Reproduction
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Subjective Results Discussion

• DCS460, inkjet combination did the best for
  sharpness, color, but 460, dye-sub system did
  better overall
• Photograph didnt perform best in any category
• For DC120, inkjet and dye-sub perform about the
  same

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System Results
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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

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Conclusions

• Interline vs. frame transfer comparison cant 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

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Review

• Gain model for digital photographic systems
• Accomplished, but
• MTF doesnt completely describe system
• Subjective evaluations for DC120, DCS460 only

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Special Thanks

• Dr. Jeff Pelz
• Dr. John Arney