TOWARDS A COMPUTATIONAL MODEL OF RETINAL STRUCTURE AND BEHAVIOR

Human vision is our most important sensory system, allowing us to perceive our surroundings. It is an extremely complex process that starts with light entering the eye and ends inside of the brain, with most of its mechanisms still to be explained. When we observe a scene, the optics of the eye focus an image on the retina, where light signals are processed and sent all the way to the visual cortex of the brain, enabling our visual sensation. The progress of retinal research, especially on the topography of photoreceptors, is often tied to the progress of retinal imaging systems. The latest adaptive optics techniques have been essential for the study of the photoreceptors and their spatial characteristics, leading to discoveries that challenge the existing theories on color sensation. The organization of the retina is associated with various perceptive phenomena, some of them are straightforward and strictly related to visual performance like visual acuity or contrast sensitivity, but some of them are more difficult to analyze and test and can be related to the submosaics of the three classes of cone photoreceptors, like how the huge interpersonal differences between the ratio of different cone classes result in negligible differences in color sensation, suggesting the presence of compensation mechanisms in some stage of the visual system. In this dissertation will be discussed and addressed issues regarding the spatial organization of the photoreceptors in the human retina. A computational model has been developed, organized into a modular pipeline of extensible methods each simulating a different stage of visual processing. It does so by creating a model of spatial distribution of cones inside of a retina, then applying descriptive statistics for each photoreceptor to contribute to the creation of a graphical representation, based on a behavioral model that determines the absorption of photoreceptors. These apparent color stimuli are reconstructed in a representation of the observed scene. The model allows the testing of different parameters regulating the photoreceptor's topography, in order to formulate hypothesis on the perceptual differences arising from variations in spatial organization

Open issues in the study of human retina

This paper reports a concise survey on some characteristics of the human retina. The goal is to present some of the known parameters together with some open issues that still do not fit in the actual models of human vision. Colour and vision in general are still far from being well known mechanisms

All the colours of a film: study of the chromatic variation of movies

In this work, we discuss and present different techniques for film colour summarization together with a preliminary colorimetric study. The aim of this project is to combine the frames of different videos, reducing them to just one image of chromatic significance. This elaboration is made through two different methods: the movie barcodes and long exposure images. Due to their nature, those concise images have not only an artistical aim, but are movies chromatic synthesis that can eventually be used for colour checks and for identification of dominances. At first, we applied those methods on two videos from the Pixar Animation Studios\u2019 short animation movies. Then, as preliminary test, we present an application on the frames of a homemade video altered in different ways together with the relative visual and numerical results

Fidarsi o no del ColorChecker?

Il ColorChecker \ue8 uno strumento usato nel campo della fotografia digitale per eseguire una calibrazione cromatica. Il pannello composto da 24 tasselli a colori viene inserito all\u2019interno di una fotografia digitale per avere una acquisizione di valori di riferimento noti. L\u2019idea \ue8 quella che conoscendo i valori del ColorChecker e correggendo quelli relativi acquisiti si pu\uf2 calibrare cromaticamente tutta l\u2019immagine. L\u2019obiettivo di questo lavoro \ue8 testare i limiti e l\u2019affidabilit\ue0 dell\u2019uso del ColorChecker. A questo scopo sono state acquisite immagini fotografiche digitali a colori contenenti il ColorChecker a diverse condizioni di illuminazione e distanze dall\u2019obiettivo. Dopo aver corretto le immagini rispetto a un punto di bianco ottenuto dall\u2019apposito tassello del ColorChecker, \ue8 stata valutata la variabilit\ue0 dei tasselli colorati rispetto ai dati di fabbrica. Sono stati inoltre misurati il range dinamico relativo del ColorChecker e la linearit\ue0 dei valori di luminanza dei tasselli in scala di grigi rapportati ai valori corrispondenti dei dati di fabbrica

Work memories in super 8: the dawn of paper recycling in Brescia

This paper describes the digital acquisition and restoration of a documentary in Super 8 of the origins of citizen\u2019s awareness on paper recycling in Brescia, a city of Lombardy, northern Italy. This short movie has been shot in 1980 by ASM the public company which used to provide all the city supply (gas, water, electricity, district heating) and city transport. Now this film is part of the Fondazione ASM archive and its acquisition is part of a larger project of preservation of industrial memories in Italy. Here we describe the tools used for the acquisition and the technical choices done, together with the restoration test made. As well, we discuss the problems that one must face in trying to preserve a visual document of this kind from the unavoidable damage of time

Use of an Occlusion Mask for Veiling Glare Removal in HDR Images

Optical systems in digital cameras present a limit during the acquisition of standard and High Dynamic Range Images (HDRI) due to the presence of veiling glare, an artifact caused by an unwanted spread of the source of light. In this paper, we analyze the state-of-the-art of veiling glare removal in HDRI, giving attention to the paper presented by Talvala. Then we describe an algorithm for veiling glare removal based on the same occlusion mask, to study the benefits provided by it in HDRI acquisition process. Finally, we demonstrate the efficiency of the occlusion mask method in veiling glare removal without any post production estimation and subtraction

Measurements of the reaction pˉp→ϕη\bar{p}p \to \phi \eta of antiproton annihilation at rest at three hydrogen target densities

The proton-antiproton annihilation at rest into the $\phi\eta$ final state was measured for three different target densities: liquid hydrogen, gaseous hydrogen at NTP and at a low pressure of 5 mbar. The yield of this reaction in the liquid hydrogen target is smaller than in the low-pressure gas target. The branching ratios of the $\phi\eta$ channel were calculated on the basis of simultaneous analysis of the three data samples. The branching ratio for annihilation into $\phi\eta$ from the $^3S_1$ protonium state turns out to be about ten times smaller as compared to the one from the $^1P_1$ state.Comment: 10 pages, 3 Postscript figures. Accepted by Physics Letters

New data on OZI rule violation in bar{p}p annihilation at rest

The results of a measurement of the ratio R = Y(phi pi+ pi-) / Y(omega pi+ pi-) for antiproton annihilation at rest in a gaseous and in a liquid hydrogen target are presented. It was found that the value of this ratio increases with the decreasing of the dipion mass, which demonstrates the difference in the phi and omega production mechanisms. An indication on the momentum transfer dependence of the apparent OZI rule violation for phi production from the 3S1 initial state was found.Comment: 11 pages, 3 PostScript figures, submitted to Physics Letter

Protonium annihilation into π0π0 at rest in a liquid hydrogen target

The annihilation frequency of the reaction p¯ p!p0p0 at rest in liquid hydrogen has been measured by the Obelix experiment by using different apparatus configurations and trigger conditions. The value obtained is f (p0p0, LH)5(2.860.1stat60.4syst)31024. With the same data samples, the p0h annihilation frequency has been determined to be f (p0h, LH)5(0.960.2stat60.1syst)31024. The results are discussed within the frame of the present experimental situation

Study of the f(0)(1500)/f(2)(1565) production in the exclusive annihilation anti-n.anti-p -> pi+.pi+.pi- in flight

The spin-parity analysis of the (n) over bar p --> pi(+)pi(+)pi(-) exclusive reaction in flight is presented. The main aim is to study the (pi(+)pi(-)) invariant mass spectrum in the region around 1500 MeV. The analysis was performed with a Breit-Wigner parametrization for all the resonant states and, for the scalar sector in the mass region below 1.2 GeV, by means of a K-matrix-like treatment. It clearly shows the need for two states, a scalar one (0(++)) with mass and width (1522+/-25) MeV and (108+/-33) MeV, and a tensorial one (2(++)) with mass (1575 +/-18) MeV and width (119+/-24) MeV, respectively. In addition, the analysis requires the presence of a scalar state at (1280+/-55) MeV, (323+/-13) MeV broad, and of a second vectorial one, in addition to the rho(0)(770) signal, with mass and width (1348+/-33) MeV and (275+/-10) MeV, respectively