Human Vision Models of Perceptual Image Distortions

Digital media's prevalence in today's society is placing an increasing strain on the technology to provide, transmit and store these contents. The demand for higher quality content in digital media has led to drastic increase in storage requirements over the past three decades. To meet the challenge of storing and securing digital media, this thesis proposes an insight into how the human vision system (HVS) can be characterized to determine thresholds of visibility of visual distortions. The use of these results can increase the amount of watermarking information applied to an image as well as applications in quantization error detection. In this thesis, we first propose a framework for predicting the regions of natural images that visually disguise distortions created as a result of modification of wavelet domain coefficients. The visual error perception algorithm adaptively predicts the visual perceptibility threshold of spread spectrum watermarking added in the wavelet subband. Spatial statistical feature maps combined with ground truth data from psychophysical experiments enabled the generation of an activity scaling parameter that evaluates the masking thresholds of image regions. We also demonstrate the correlation with an image quality assessment algorithm to the detectability of distortions in an image. Subsequently the algorithm is combined with a compression scheme to yield compressed images of higher visual quality. Secondly, we presents the results of another psychophysical experiment designed to investigate the effect of a scene's context on the detection of distortions presented in natural-image patches. Via a two-alternative forced-choice experiment, we measured thresholds for detecting 6.2 c/deg gabor target in image patches which were placed in various image surrounds (contexts), including various textures, a solid-gray background, and the patch's original context. The contexts were adjusted using histogram specification to control for differences in brightness, contrast, and other first-order statistical properties of the luminance distribution. Our results revealed that the context in which a patch is placed does indeed affect the ability to detect distortions in that patch. The findings suggest that characterization and implementation of a human visual system's ability to detect errors has potential in providing perceivable greater quality in image applications.School of Electrical & Computer Engineerin

Uticaj fedinga na komunikaciju senzorskih čvorova u bežičnim nosivim telesnim senzorskim mrežama za vojnu primenu

Svakodnevno se uvećavaju zahtevi za informacijama u procesu odlučivanja. Savremena bojišta svakako nisu izuzetak, jer se na osnovu tačnih i pravovremenih informacija mogu donositi odluke koje na kraju mogu spasiti ljudske živote, smanjiti upotrebu prekomerne sile ili pak uništenje vojne tehnike. Količine i vrste podataka koje senzorske mreže generišu na samom terenu postavljaju tehničke izazove pred komunikacionu tehniku da obezbede pravilan, potpun i bezbedan način protoka informacija. Jedan od problema koji je potrebno istražiti je komunikacija bežičnih senzorskih mreža koje imaju nove karakteristike i zahteve na komunikacionim sistemima i mrežnim protokolima, a koji se razlikuju od konvencionalnih mreža za komunikaciju podataka. Pojava fedinga u bežičnim senzorskim mrežama je sigurna, ali sam sistem svojom konfiguracijom senzorskih čvorova i kombinacijom bežičnih tehnologija čini da se interferencija u kanalu smanji i poveća kapacitet protoka samog kanala. Bežične senzorske mreže se organizuju u hijerarhiskom i ćelijskom nivou. S druge strane veliki broj ćelija utiče da se poveća i broj radio kanala, a sa povećanjem broja radio kanala dolazi do međukanalne interferencije što direktno utiče kvalitet prenosa podataka radio kanalom. Cilj je postići potreban nivo kapaciteta u prenosu i kvaliteta u prijemu signal na krajnoj tački. Dodatak, konvencionalnim RF sistemima komunikacije, u obliku FSO komunikacionih sistema predstavljaju značajno unapređenje koje može unaprediti performanse, brzine prenosa i bezbedniji prenos podataka. U radu je predložena hibridna RF/FSO mobilna senzorska mreža koja uspešno treba za prevaziđe komunikacione probleme konvencionalne RF mreže. U radu je istražena mogućnost da se kroz optički kanal u prisustva fedinga (scintilacije) prenesu kompleksniji podaci (slika, video i sl.), kao i kako u prisustvu fedinga u optičkom kanalu dolazi do degradacije podatka