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

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

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

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%

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)

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

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 30-100% 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

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. 361-369, Aug 2004. V. Monga, N. Damera-Venkata, B. Evans, Halftoning Toolbox for Matlab. Version 1.1 released November 7, 2002. Available online at http://www.ece.utexas.edu/~bevans/projects/halftoning/.