It is now common practice to monitor imaging performance prior to, and during, image acquisition. While these methods have been applied to near-flat objects and documents, less attention has been given to developing reliable methods for two-dimensional perspective images, where optical depth-of-field can be critical. we describe results of our effort to adapt standard methods to this new application. Cameras using simple, fixed lens and a tilted lens were evaluated.

1. 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

2. 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
2
Object-level target

3. 2-D projection images
3
Test objects
• Aimed at visual evaluation if
lens focus
• Note fixed geometry

4. Object-level targets
4
Arthur M. Sackler and Freer Galleries of Art
1
2
3
• 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

5. Example use of test targets
5
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

6. Use of tilted test chart
• Tilt target to cover depth of
object
• Repeated test features now
sample scene depth
6
camera
lens
chart
holder
test
chart
Holder courtesy of Image Science
Associates
• Adjustable chart holder
• Maintains object depth as
camera angle is adjusted

7. Experiment
7
• 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

8. View camera
8
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

9. Fixed-lens results
9
0 5 10 15
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency, cy/mm
SFR
1
2
3
1
2
3

10. Tilted-lens results
10
1
2
3
0 5 10 15
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Frequency, cy/mm
SFR
1
2
3

11. Simplified edge target
11
• Nikon DSLR camera, zoom lens
• Simple extended edge for image
resolution
• Uniform areas to evaluate illumination
variation
Single edge
chart
Test image

12. Camera aperture series
12
• Capture series oft test images varying lens aperture setting
• Automated evaluation of image depth of focus

13. Aperture series results
13

14. Illumination profile measurement
14
• Illumination profile based on light
uniform chart region
• Computed are average pixel row in
the region
Single edge
chart
Distance, cm
0 1 2 3 4 5 6 7 8 9
Profile
180
185
190
195
200
205
210
215
220
225
230
• Uniform lighting may not be
the goal
• Consistency normally is

15. 15
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

16. Acknowledgements:
16
Many thanks to Picturae BV team working at the Cooper Hewitt,
Smithsonian Design Museum
Handmade toy train, UK c. 1958