Joaquín Fernández-Valdivia

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We present a number of autofocusing methods in lighting microscopy for its use in diatom identi cation. Among these, the Tenengrad method has been considered one of the best. The basic requirements for a practical autofocusing system are speed, sharpness and robustness to noise. Recently other focus measures based on a modi ed Laplacian method are said to(More)
This paper analyzes how the natural scales of the shapes in 2D images can be extracted. Spatial information is analyzed by multiple units sensitive to both spatial and spatial-frequency variables. Scale estimates of the relevant shapes are constructed only from strongly responding detectors. The meaningful structures in the response of a detector (computed(More)
ÐIt is of great benefit to have advance knowledge of human visual target acquisition performance for targets or other relevant objects. However, search performance inherently shows a large variance and depends strongly on prior knowledge of the perceived scene. A typical search experiment therefore requires a large number of observers to obtain(More)
In this paper, a new frequency-domain approach to represent motions is proposed. The new scheme is based on a band-pass filtering with a set of logGabor spatio-temporal filters. It is well known that one of the main problems of these approaches is that a filter response varies with the spatial orientation of the underlying signal. To solve this spatial(More)
In this paper we provide the reader with a visual representation of relationships among the impact of book chapters indexed in the Book Citation Index using information gain values and published by different academic publishers in specific disciplines. The impact of book chapters can be characterized statistically by citations histograms. For instance, we(More)
ÐThis paper describes a system for the automatically learned partitioning of avisual patternso in 2D images, based on a sophisticated, band-pass, filtering operation with fixed scale and orientation sensitivity. In this scheme, the avisual patternso are defined as the features which have the highest degree of alignment in the statistical structure across(More)
This paper introduces a new method for clustering data using a dynamic scheme. An appropriate partitioning is obtained based on both a dissimilarity measure between pairs of entities as well as a dynamic procedure of splitting. A dissimilarity function is de ned by using the cost of the optimum path from a datum to each entity on a graph, with the cost of a(More)
This paper introduces a new approach to solving the problem of representing planar curves. We describe the 2-D curve C not at all diierent scales , but each curve part C i of C, isolating a diierent structure at its single scale i. Therefore, we represent the planar curve at a scale vector (1 ; ; L) supposing that the curve is partitioned in L parts C 1 ; ;(More)
In this paper we present three error measures based on feature perception models, in which pixel errors are computed on locations at which humans might perceive features in the reference image. In the first part of this work, the three schemes of feature detection will be discussed and evaluated in terms of their performance for a simple visual(More)
This paper presents a method for selecting proper scale parameters for edge detection. To this aim the image is preliminarily segmented into regions with a homogeneous intensity change model, by using a clustering algorithm based on a dissimilarity measure applied on feature vectors associated to the regions. The used algorithm is a standard clustering(More)