1. Thayne Coffman EE381K-14 May 3, 2005
The Frequency-Domain Effects of Stochastic Image Foveation in Superpixelating Cameras
Thayne Coffman
EE381K-14
May 3, 2005

2. Review – Motivation and Objective
Superpixellating (“VASI”) cameras
Translation of desired resolution to control signal can be done by halftoning
Which halftoning method will give the best ATR performance?
Block error diffusion
Blue noise dithering
Floyd & Steinberg error diffusion
Raster scan
Serpentine scan
Classical screening
9-level clustered dot
9-level dispersed dot
White noise
A method of my own design
vasiHalftone, vasiHalftone2
Not exactly halftoning algorithms
[McCarley et al, 2004]
Performance measured by
PSNR
WSNR
LDM (not a useful differentiator)
UQI

3. Nontrivial Translation of Control Signal
Control signal vs. realized bandwidth
Nontrivial relationship caused by the geometry of pixel sharing patterns
Requires customization (inverse function) of control signal for each halftoning method
Stairstep patterns limit your control over actual realized bandwidth
Details in paper

4. My Custom Methods – vasiHalftone, vasiHalftone2
Semi-regularly spaced rectangles, size depends on desired bandwidth
For a given control signal
Consistently superior PSNR & WSNR
Consistently overshot desired bandwidth by ~30-100%
They were essentially cheating by using extra bandwidth
As currently designed, these methods have very poor bandwidth control
Original
Sharing Signal
Resulting Image
PSNR = 13.3 dB
WSNR = 16.9 dB
Desired BW = 9.6%
Actual BW = 18.8%
Inflation = 97%

5. F&S Error Diffusion Good performance and good bandwidth control
Good SNR in ROIs means accurate ATR
Good SNR in non-ROIs means good target acquisition
Good bandwidth control means precise VASI frame rate control
Original
Sharing Signal
Resulting Image
Desired BW = 11.6%
Actual BW = 12.1%
Inflation = 4%
PSNR = 17.5 dB (33.3 dB in ROI)
WSNR = 16.4 dB (33.8 dB in ROI)

6. The Rest Method Performance (SNR) Bandwidth control
Block error diffusion
Poor
Good
Classical screening
Decent
Stochastic methods
Suceptible to “catastrophic gray-out”
Original
Block error diffusion
Blue noise
Original
Clustered dot
Dispersed dot
White noise

7. Conclusions
Floyd & Steinberg error diffusion gives the best results while still being able to control bandwidth precisely
vasiHalftone & vasiHalftone2
Consistently the best PSNR, WSNR
Poor bandwidth control – overshot specifications by %
Bandwidth inflation means it’s not a fair comparison (they’re cheating)
Stochastic methods (white & blue noise) perform poorly
Outperformed by deterministic approaches
Susceptible to “catastrophic gray-out”
Classical screening performs marginally and has bad bandwidth control

8. References
P. McCarley, M. Massie, J.P. Curzan, “Large format variable spatial acuity superpixel imaging: visible and infrared systems applications,” Proc. SPIE, Infrared Technology and Applications XXX[sic.], vol. 5406, pp , Aug 2004.
V. Monga, N. Damera-Venkata, B. Evans, Halftoning Toolbox for Matlab. Version 1.1 released November 7, Available online at