Xavier Otazu

Xavier Otazu
Autonomous University of Barcelona | UAB · Department of Computer Sciences

BSc Physics, MSc Remote Sensing; PhD Physics

About

79
Publications
11,114
Reads
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2,723
Citations
Additional affiliations
September 2000 - present
Autonomous University of Barcelona
Position
  • Professor (Associate)
September 2000 - present
CVC Computer Vision Center
Position
  • Senior Researcher
June 1994 - November 2001
University of Barcelona
Position
  • PhD Student

Publications

Publications (79)
Article
Full-text available
Color induction is the phenomenon where the physical and the perceived colors of an object differ owing to the color distribution and the spatial configuration of the surrounding objects. Previous works studying this phenomenon on the lsY MacLeod-Boynton color space, show that color assimilation is present only when the magnocellular pathway (i.e.,...
Article
Full-text available
The human visual system is not a colorimeter. The perceived colour of a region does not only depend on its colour spectrum, but also on the colour spectra and geometric arrangement of neighbouring regions, a phenomenon called chromatic induction. Chromatic induction is thought to be driven by lateral interactions: the activity of a central neuron i...
Article
Previous studies suggested that lateral interactions of V1 cells are responsible, among other visual effects, of bottom-up visual attention (alternatively named visual salience or saliency). Our objective is to mimic these connections with a neurodynamic network of firing-rate neurons in order to predict visual attention. Early visual subcortical p...
Preprint
Full-text available
A benchmark of saliency models performance with a synthetic image dataset is provided. Model performance is evaluated through saliency metrics as well as the influence of model inspiration and consistency with human psychophysics. SID4VAM is composed of 230 synthetic images, with known salient regions. Images were generated with 15 distinct types o...
Conference Paper
Full-text available
A benchmark of saliency models performance with a synthetic image dataset is provided. Model performance is evaluated through saliency metrics as well as the influence of model inspiration and consistency with human psy-chophysics. SID4VAM is composed of 230 synthetic images , with known salient regions. Images were generated with 15 distinct types...
Preprint
Full-text available
Previous studies in that line suggested that lateral interactions of V1 cells are responsible, among other visual effects, of bottom-up visual attention (alternatively named visual salience or saliency). Our objective is to mimic these connections in the visual system with a neurodynamic network of firing-rate neurons. Early subcortical processes (...
Article
Color induction is the influence of the surrounding color (inducer) on the perceived color of a central region. There are two different types of color induction: color contrast (the color of the central region shifts away from that of the inducer) and color assimilation (the color shifts towards the color of the inducer). Several studies on these e...
Article
In this study we provide the analysis of eye movement behavior elicited by low-level feature distinctiveness with a dataset of synthetically-generated image patterns. Design of visual stimuli was inspired by the ones used in previous psychophysical experiments, namely in free-viewing and visual searching tasks, to provide a total of 15 types of sti...
Preprint
Full-text available
Computations in the primary visual cortex (area V1 or striate cortex) have long been hypothesized to be responsible, among several visual processing mechanisms, of bottom-up visual attention (also named saliency). In order to validate this hypothesis, images from eye tracking datasets are processed with a biologically plausible model of V1 able to...
Preprint
Full-text available
In this study we provide the analysis of eye movement behavior elicited by low-level feature distinctiveness with a dataset of synthetically-generated image patterns. Design of visual stimuli was inspired by the ones used in previous psychophysical experiments, namely in free-viewing and visual searching tasks, to provide a total of 15 types of sti...
Article
Full-text available
The color appearance of a surface depends on the color of its surroundings (inducers). When the perceived color shifts towards that of the surroundings, the effect is called "color assimilation" and when it shifts away from the surroundings it is called "color contrast." There is also evidence that the phenomenon depends on the spatial configuratio...
Preprint
Full-text available
Color induction is the influence of the surrounding color (inducer) on the perceived color of a central region. There are two different types of color induction: color contrast (the color of the central region shifts away from that of the inducer) and color assimilation (the color shifts towards the color of the inducer). Several studies on these e...
Article
Full-text available
Tone-mapping operators (TMO) are designed to generate perceptually similar low-dynamic range images from high-dynamic range ones. We studied the performance of fifteen TMOs in two psychophysical experiments where observers compared the digitally generated tone-mapped images to their corresponding physical scenes. All experiments were performed in a...
Poster
Full-text available
Previous psychophysical research show that saliency is elucidated during the first and second saccade. Latest research using computational models for saliency prediction promote increasing patterns of prediction error in saccade landing and saccade amplitude with respect to the saccade number, suggesting the scepticism of including specific fixatio...
Poster
Full-text available
Attention processing mechanisms have been proved to be influenced by the primary visual cortex activity. Attention maps, named saliency maps, are the representation of the most relevant cues that attract attention given a specific stimulus, either synthetic or real images. These saliency maps have been predicted using artificial as well as biologic...
Conference Paper
High-dynamic-range (HDR) imaging refers to the methods designed to increase the brightness dynamic range present in standard digital imaging techniques. This increase is achieved by taking the same picture under different exposure values and mapping the intensity levels into a single image by way of a tone-mapping operator (TMO). Currently, there i...
Article
Full-text available
We propose a saliency model termed SIM (saliency by induction mechanisms), which is based on a low-level spatiochromatic model that has successfully predicted chromatic induction phenomena. In so doing, we hypothesize that the low-level visual mechanisms that enhance or suppress image detail are also responsible for making some image regions more s...
Conference Paper
Historical documents suffer from different types of degradation and noise such as background variation, uneven illumination or dark spots. In case of double-sided documents, another common problem is that the back side of the document usually interferes with the front side because of the transparency of the document or ink bleeding. This effect is...
Article
Full-text available
Brightness induction is the modulation of the perceived intensity of an area by the luminance of surrounding areas. Recent neurophysiological evidence suggests that brightness information might be explicitly represented in V1, in contrast to the more common assumption that the striate cortex is an area mostly responsive to sensory information. Here...
Data
Supplementary Material. Neurodynamical model of contextual influences mediated by intra-cortical interactions in V1 (following [35]). Proposed model parameters. (PDF)
Data
Full-text available
Supplementary Material. Supplementary results (Figure S1 in Text S3 and Figure S2 in Text S3). (PDF)
Data
Full-text available
Supplementary Material. Wavelet analysis. (PDF)
Data
Full-text available
Supplementary Material. Frequency gain of the model (Figure S3 in Text S4). (PDF)
Article
Normalization of signals coming from linear sensors is an ubiquitous mechanism of neural adaptation.1 Local interaction between sensors tuned to a particular feature at certain spatial position and neighbor sensors explains a wide range of psychophysical facts including (1) masking of spatial patterns, (2) non-linearities of motion sensors, (3) ada...
Conference Paper
Full-text available
Background / Purpose: We aimed to reproduce brightness induction by using a neurodynamical model of V1 that considers contextual influences. Main conclusion: Both brightness induction and visual saliency can be modeled by a common neurodynamical architecture.
Article
Image retrieval can be dealt by combining standard descriptors, such as those of MPEG-7, which are defined independently for each visual cue (e.g. SCD or CLD for Color, HTD for texture or EHD for edges). A common problem is to combine similarities coming from descriptors representing different concepts in different spaces. In this paper we propose...
Conference Paper
Full-text available
In this work we present an effective and computationally simple algorithm for image compression based on Hilbert Scanning of Embedded quadTrees (Hi-SET). It allows to represent an image as an embedded bitstream along a fractal function. Embedding is an important feature of modern image compression algorithms, in this way Salomon in [1, pg. 614] cit...
Conference Paper
Full-text available
Many successful models for predicting attention in a scene involve three main steps: convolution with a set of filters, a center-surround mechanism and spatial pooling to construct a saliency map. However, integrating spatial information and justifying the choice of various parameter values remain open problems. In this paper we show that an effici...
Conference Paper
Full-text available
The perceived colour of a stimulus is dependent on multiple factors stemming out either from the context of the stimulus or idiosyncrasies of the observer. The complexity involved in combining these multiple effects is the main reason for the gap between classical calibrated colour spaces from colour science and colour representations used in compu...
Conference Paper
In this work we present an effective and computationally simple algorithm for image compression based on Hilbert Scanning of Embedded quadTrees (Hi-SET). It allows to represent an image as an embedded bitstream along a fractal function. Embedding is an important feature of modern image compression algorithms, in this way Salomon in [1, pg. 614] cit...
Article
The aim of writer identification is determining the writer of a piece of handwriting from a set of writers. In this paper, we present an architecture for writer identification in old handwritten music scores. Even though an important amount of music compositions contain handwritten text, the aim of our work is to use only music notation to determin...
Article
Full-text available
In a previous work (X. Otazu, M. Vanrell, & C. A. Párraga, 2008b), we showed how several brightness induction effects can be predicted using a simple multiresolution wavelet model (BIWaM). Here we present a new model for chromatic induction processes (termed Chromatic Induction Wavelet Model or CIWaM), which is also implemented on a multiresolution...
Conference Paper
Full-text available
Color and texture are visual cues of different nature, their integration in a useful visual descriptor is not an obvious step. One way to combine both features is to compute texture descriptors independently on each color channel. A second way is integrate the features at a descriptor level, in this case arises the problem of normalizing both cues....
Conference Paper
Full-text available
Color and texture are visual cues of different nature, their integration in an useful visual descriptor is not an easy problem. One way to combine both features is to compute spatial texture descriptors independently on each color channel. Another way is to do the integration at the descriptor level. In this case the problem of normalizing both cue...
Article
Full-text available
In this paper we show how the techniques of image deconvolution can increase the ability of image sensors as, for example, CCD imagers, to detect faint stars or faint orbital objects (small satellites and space debris). In the case of faint stars, we show that this benefit is equivalent to double the quantum efficiency of the used image sensor or t...
Article
Full-text available
On September 8, 2001 around 2 h UT, the largest uranian moon, Titania, occulted Hipparcos star 106829 (alias SAO 164538, a V=7.2, K0 III star). This was the first-ever observed occultation by this satellite, a rare event as Titania subtends only 0.11 arcsec on the sky. The star's unusual brightness allowed many observers, both amateurs or professio...
Article
Full-text available
On September 8, 2001 around 2 h UT, the largest uranian moon, Titania, occulted Hipparcos star 106829 (alias SAO 164538, a V = 7.2, KO III star). This was the first-ever observed occultation by this satellite. a rare event as Titania subtends only 0.11 arcsec on the sky. The star's unusual brightness allowed many observers, both amateurs or profess...
Article
A new multiresolution wavelet model is presented here, which accounts for brightness assimilation and contrast effects in a unified framework, and includes known psychophysical and physiological attributes of the primate visual system (such as spatial frequency channels, oriented receptive fields, contrast sensitivity function, contrast non-lineari...
Article
Full-text available
The introduction of infrared arrays for lunar occultations (LO) work and the improvement of predictions based on new deep IR catalogues have resulted in a large increase in the number of observable occultations. We provide the means for an automated reduction of large sets of LO data. This frees the user from the tedious task of estimating first-gu...
Article
In this paper, we present a wavelet based approach which tries to automatically find the number of clusters present in a data set, along with their position and statistical properties. The only information supplied to the method is the data set to analyze and a confidence level parameter. Most of the usual methods for cluster analysis and unsupervi...
Article
Full-text available
Spatial resolution is a key parameter of all remote sensing satellites and platforms. The nominal spatial resolution of satellites is a well-known characteristic because it is directly related to the area in ground that represents a pixel in the detector. Nevertheless, in practice, the actual resolution of a specific image obtained from a satellite...
Article
Full-text available
Probably the most popular image fusion method is that based on the intensity-hue-saturation (IHS) transform. Although the spatial enhancement of the IHS-merged images is high, the distortion of its spectral information may also be important. In recent years, several methods have been developed to minimize this problem, being those based on wavelets...
Article
Full-text available
We show how a wavelet-based image adaptive deconvolution algorithm can provide significant improvements in the analysis of wide-field CCD images. To illustrate it, we apply our deconvolution protocol to a set of images from a Baker-Nunn telescope. This f/1 instrument has an outstanding field of view of 4.4°x4.4° with high optical quality offering u...
Article
Full-text available
We show how wavelet-based image deconvolution can provide to wide-field CCD telescopes an increase in limiting magnitude of R0:6 and significant deblending improvement. Astrometric accuracy is not distorted, therefore, the feasibility of the technique for astrometric projects is validated. We apply the deconvolution process to a set of images from...
Article
Full-text available
We present an update of the lunar occultation program which is routinely carried out in the near-IR at the Calar Alto Observatory. A total of 350 events were recorded since our last report (Fors et al. 2004, A&A, 419, 285). In the course of eight runs we have observed, among others, late-type giants, T-Tauri stars, and infrared sources. Noteworthy...
Article
Full-text available
Usual image fusion methods inject features from a high spatial resolution panchromatic sensor into every low spatial resolution multispectral band trying to preserve spectral signatures and improve spatial resolution to that of the panchromatic sensor. The objective is to obtain the image that would be observed by a sensor with the same spectral re...
Article
that is a computational repre- sentation of the image that provides us with the appear- ance information of the image content. Appearance depends on the observation distance, as well as consid- erations on the physiological attributes of the human visual system, since acquisition devices does not act exactly as the human visual system does. In this...
Article
Full-text available
In the last few years, several researchers have proposed different procedures for the fusion of multispectral and panchromatic images based on the wavelet transform, which provide satisfactory high spatial resolution images keeping the spectral properties of the original multispectral data. The discrete approach of the wavelet transform can be perf...
Conference Paper
Full-text available
In this paper we present an unsupervised colour-texture segmentation method. The novelty of this new approach relies on the definition of the interfeature distance map, which combines different textural properties, either those due to chromaticity variations or those due to intensity changes. The proposed framework works on a multi-channel represen...
Article
Spatial resolution is a key parameter of all kind of images. This is of particular importance in fields as, for example, medicine or remote sensing. The nominal resolution of a positron emission tomography (PET) or nuclear magnetic resonance (NMR) scanners are directly related to the size, number, and position of the detectors in the scanner ring....
Article
In this paper we present a multiresolution-based method for period determination that is able to deal with unevenly sampled data. This method allows us to detect superimposed periodic signals with lower signal-to-noise ratios than in classical methods. This multiresolution-based method is a generalization of the wavelet-based method for period dete...
Article
In this paper we present a wavelet-based algorithm that is able to detect superimposed periodic signals in data with low signal-to-noise ratio. In this context, the results given by classical period determination methods depend strongly on the intrinsic characteristics of each periodic signal, like amplitude or profile. It is then difficult to dete...
Article
We present a study of the long-term X-ray variability of the high mass X-ray binary SMC X-1 based on four and a half years of ASM/RXTE data. A decreasing period from ~60 to ~50 days using the first ~500 d of data was reported in the literature. Our analysis, based on the use of wavelets and standard techniques, shows that the period seems to be mod...
Article
We have performed a ROSAT follow-up observation of the X-ray transient SAX J1810.8-2609 on March 24, 1998 and detected a bright X-ray source (named RX J1810.7-2609) which was not detected during the ROSAT all-sky survey in September 1990. Optical-to-infrared follow-up observations of the 10 arcsec radius ROSAT HRI X-ray error box revealed one varia...
Article
Full-text available
The standard data fusion methods may not be satisfactory to merge a high-resolution panchromatic image and a low-resolution multispectral image because they can distort the spectral characteristics of the multispectral data. The authors developed a technique, based on multiresolution wavelet decomposition, for the merging and data fusion of such im...
Article
Full-text available
A technique based on multiresolution wavelet decomposition was developed for the merging and data fusion of a high-resolution panchromatic image and a low-resolution multispectral image. The standard data fusion methods may not be satisfactory, because they can distort the spectral characteristics of the multispectral data. The method presented her...
Article
Full-text available
In this paper we present the development of a technique, based on multiresolution wavelet decomposition, for the merging and data fusion of a high-resolution panchromatic image and a low- resolution multispectral image. The method presented here consists of adding the wavelet coefficients of the high- resolution image to the multispectral (low-reso...
Article
In this paper we present a technique, based on multiresolution wavelet decomposition, for the merging and data fusion of two images. The images to merge are a high-resolution panchromatic image and a low-resolution multispectral image. The method consists of adding the wavelet coefficients of the high-resolution image to the multispectral (low-reso...
Article
This paper presents two methods to overcome the problem of noise amplification during the image reconstruction process. The first method responds to the premise that the resolution sought in the reconstruction of different parts of an image should depend on the statistical quality of the corresponding data. The authors have developed a method that...
Article
To overcome the problem of noise amplification during the image reconstruction process, we present a new method based on wavelet decomposition. After decomposing the raw image to be reconstructed into several wavelet planes and a residual image, we reconstruc