1,721,122 research outputs found
A multiscale contrast enhancement method
No full textThis paper contributes a novel approach to contrast enhancement. The proposed approach measures focal contrast within the context of a non-linear scale-space representation. The original image is locally probed at multiple resolutions generated through anisotropic diffusion. Once local contrast has been estimated across an optimal range of scales, its value is used to enhance the initial image. Due to the choice of the anisotropic seals-space, the method also accounts for non-linear edge contributes
Struttura, informazione, modelli : il contributo di Valentino Braitenberg
Full text linkBraitenberg's neuroanatomical research was carried out in the endeavour to identify the network structures specific to a given part of the brain. But, more generally, his work concerns the functional interpretation of brain structures. Yet, since computers came into play in the 1950s, Braitenberg was well aware of their potential for bridging the gap between neuronal structures and mechanisms, namely, for building up models of brain functions. In this paper we shall argue that the relationships between structure, information and models constitute the spine of Braitenberg's systemic-cybernetic thinking. In a nutshell, the quest for a model calls for the interplay between structure and information. Meanwhile, defining information in terms of structure leads to reconsider the meaning of a model at a certain level of explanation. In this perspective, we begin by discussing his noteworthy contributions to functional neuroanatomy, in particular those related to charting the visual cortex, where Braitenberg explicitly addresses the issue of how to set up a model so to in efficiently account for the underlying neural mechanisms. Then, we consider his unconventional approach to the concept of information, which is shaped in terms of structural information, rendering it a powerful tool for understanding and thus modelling the neural mechanisms of cognitive functions. The paper concludes by suggesting and discussing some implications of Braitenberg's view for most recent and lively debate on models and levels of explanation in the behavioural sciences
Information properties in fine-to-coarse image transformations
No full textThe notion of entropy production, as defined by the thermodynamics of irreversible transformations, is used to quantify information loss during a transformation from fine-to-coarse image representations. To this aim we first show the existence of a precise relation between entropy production and the Kullback-Leibler distance. This relation allows one to gauge local and global information losses which are associated with the global and local information content information of the images. Connections between the proposed approach, segmentation issues, and classical information theory are discussed
Nonparametric Bayesian attentive video analysis
Full text linkWe address the problem of object-based visual attention from a Bayesian standpoint. We contend with the issue of joint segmentation and saliency computation
suitable to provide a sound basis for dealing with higher level information related to objects present in dynamic
scene. To this end we propose a framework relying on nonparametric Bayesian techniques, namely variational inference on a mixture of Dirichlet processes
Anisotropic enhancement of mammographic images
No full textFilters for mammography based on anisotropic diffusion are introduced and evaluated with respect to well known filters adopted within this field. Results reported concern with images including microcalcifications. The performances of anisotropic filters are assessed both on the basis of figures of merit, allowing a preliminary quantitative enhancement evaluation, and according to goal-directed evaluation relying upon a simple segmentation module. Results indicate that proposed filters exhibit an effective and appealing behavior but they are subject to a more complex tuning, if compared to traditional filters
Ecological sampling of gaze shifts
Full text linkVisual attention guides our gaze to relevant parts of the viewed scene, yet the moment-to-moment relocation of gaze can be different among observers even though the same locations are taken into account. Surprisingly, the variability of eye movements has been so far overlooked by the great majority of computational models of visual attention. In this paper we present the ecological sampling model, a stochastic model of eye guidance explaining such variability. The gaze shift mechanism is conceived as an active random sampling that the foraging eye carries out upon the visual landscape, under the constraints set by the observable features and the global complexity of the landscape. By drawing on results reported in the foraging literature, the actual gaze relocation is eventually driven by a stochastic differential equation whose noise source is sampled from a mixture of α-stable distributions. This way, the sampling strategy proposed here allows to mimic a fundamental property of the eye guidance mechanism: where we choose to look next at any given moment in time, it is not completely deterministic, but neither is it completely random To show that the model yields gaze shift motor behaviors that exhibit statistics similar to those displayed by human observers, we compare simulation outputs with those obtained from eye-tracked subjects while viewing complex dynamic scenes
Modelling eye-movement control via constrained search approach
No full textA model of visual search is presented where gaze shifts are driven by an hybrid deterministic/stochastic mechanism operating
over a saliency field. Results of the simulations are compared with experimental data, and a notion of complexity is used to quantify the behaviour of the system in different condition
Predictive brains : forethought and the levels of explanation
Full text linkIs any unified theory of brain function possible? Following a line of thought dating back to the early cybernetics (see, e.g., Cordeschi, 2002), Clark (in press) has proposed the action-oriented Hierarchical Predictive Coding (HPC) as the account to be pursued in the effort of gaining the “Grand Unified Theory of the Mind”—or “painting the big picture,” as (Edelman 2012) put it. Such line of thought is indeed appealing, but to be effectively pursued it should be confronted with experimental findings and explanatory capabilities (Edelman, 2012).
The point we are making in this note is that a brain with predictive capabilities is certainly necessary to endow the agent situated in the environment with forethought or foresight, a crucial issue to outline the unified account advocated by Clark. But the capacity for forethought is deeply entangled with the capacity for emotions and when emotions are brought into the game, cognitive functions become part of a large-scale functional brain network. However, for such complex networks a consistent view of hierarchical organization in large-scale functional networks has yet to emerge (Bressler and Menon, 2010), whilst heterarchical organization is likely to play a strategic role (Berntson et al., 2012). This raises the necessity of a multilevel approach that embraces causal relations across levels of explanation in either direction (bottom–up or top–down), endorsing mutual calibration of constructs across levels (Berntson et al., 2012). Which, in turn, calls for a revised perspective on Marr's levels of analysis framework (Marr, 1982). In the following we highlight some drawbacks of Clark's proposal in addressing the above issues
Coupling the world with the observer: from analysis of information to active vision
No full textIn this paper we define the content of information in an image and show how it can be computed by taking into account different levels of resolution, in the framework of information theory and the thermodynamics of irreversible transformations. The results thus obtained wil l eventual ly be exploited to derive a mechanism for active exploration of visual space suitable to perform a dynamic coupling between the agent and its environmen
- …
