Evaluation of 3D-Projection Image Capture

Peter D. Burns, Burns Digital Imaging Don Williams, Image Science Associates

pdburns@ieee.org

© 2015 Peter D. Burns and Don Williams

Introduction • Now common to monitor imaging performance for acquisition • Important aspects of imaging practice influence

• Lighting • Camera position and settings • Lens selection and settings

• We now have guidelines for controlling variation • FADGI Guidelines • Metamorfoze Preservation Imaging Guidelines

• What about 3D objects? • Can we adapt current methods? • Simple, repeatable evaluation

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Object-level target

2-D projection images

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Test objects

• Aimed at visual evaluation if lens focus

• Note fixed geometry

Object-level targets

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Arthur M. Sackler and Freer Galleries of Art 1

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• Intra-image variation

• Repeated edge features to measure image resolution

• 3 measurements for 3 positions

• Used to monitor performance

• Quality assurance for digital collections

• Mostly used for near-flat objects and documents

• Inter-image variation measurement

Example use of test targets

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Arthur M. Sackler and Freer Galleries of Art

• Test chart normal to lens axis

• Works well for evaluating imaging performance in primary plane through the object

camera lens

chart holder

test chart

• What about performance with scene depth ?

- Optical depth of field

Use of tilted test chart • Tilt target to cover depth of

object

• Repeated test features now sample scene depth

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cameralens

chartholder

testchart

Holder courtesy of Image Science Associates

• Adjustable chart holder

• Maintains object depth as camera angle is adjusted

Experiment

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• Image capture at Cooper Hewitt, Smithsonian Design Museum

• Mass digitization effort, Nov. 2014

• Measure image resolution as per standard methods

• Test chart

• Analysis software

• Adapt to sample scene depth

• Digital view camera by Picturae BV

• Upper part of test chart is tilting way from camera

View camera

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Film or detector plane

Lens plane

Plane of Sharp focus

Lens axis

Scheimpflug intersection

• Lens is tilted to vary the plane of sharp focus

• Used in architectural photography to change camera perspective

Fixed-lens results

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0 5 10 150

0.1

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0.7

0.8

0.9

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Frequency, cy/mm

SFR

123

1

2

3

Tilted-lens results

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1

2

3

0 5 10 150

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Frequency, cy/mm

SFR

123

Simplified edge target

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• Nikon DSLR camera, zoom lens

• Simple extended edge for image resolution

• Uniform areas to evaluate illumination variation

Single edgechart

Test image

Camera aperture series

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• Capture series oft test images varying lens aperture setting

• Automated evaluation of image depth of focus

Aperture series results

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Illumination profile measurement

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• Illumination profile based on light uniform chart region

• Computed are average pixel row in the region

Single edge chart

Distance, cm0 1 2 3 4 5 6 7 8 9

Prof

ile

180

185

190

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200

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215

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225

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• Uniform lighting may not be the goal

• Consistency normally is

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Conclusions

1. Methods and tools for monitoring of imaging performance are well-established for near flat objects

2. We investigated adapting these for 2D, perspective images of 3D objects

• Both DSLR and view camera testing was completed

• Objective-level test targets

• Tilted chart used to sample scene depth

• Chart holder with adjustable angle

3. Image resolution • Multiple region selection • Reference analysis (unchanged) was used

4. illumination uniformity evaluated

Acknowledgements:

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Many thanks to Picturae BV team working at the Cooper Hewitt, Smithsonian Design Museum

Handmade toy train, UK c. 1958