Papers by Javier Portilla
IEEE Trans. on Aerospace …, 1993
Page 1. Title: TEXTURE SYNTHESIS-BY-ANALYSIS BASED ON A MULTISCALE EARLY-VISION MODEL. Authors:... more Page 1. Title: TEXTURE SYNTHESIS-BY-ANALYSIS BASED ON A MULTISCALE EARLY-VISION MODEL. Authors: Javier Portilla, Rafael Navarro, Oscar Nestares and Antonio Tabernero*. Address: Instituto de Optica (CSIC). Serrano 121. 28006 Madrid. Spain. ...
Abstract. A new texture synthesis-by-analysis method, applying a visu-ally based approach that ha... more Abstract. A new texture synthesis-by-analysis method, applying a visu-ally based approach that has some important advantages over more traditional texture modeling and synthesis techniques is introduced. The basis of the method is to encode the textural information by sampling ...
2020 IEEE 22nd International Workshop on Multimedia Signal Processing (MMSP)
Feature adjustment, understood as the process aimed at modifying at will global features of given... more Feature adjustment, understood as the process aimed at modifying at will global features of given signals, has cardinal importance for several signal processing applications, such as enhancement, restoration, style transfer, and synthesis. Despite of this, it has not yet been approached from a general, theory-grounded, perspective. This work proposes a new conceptual and practical methodology that we term Controlled Feature Adjustment (CFA). CFA provides methods for, given a set of parametric global features (scalar functions of discrete signals), (1) constructing a related set of deterministically decoupled features, and (2) adjusting these new features in a controlled way, i.e., each one independently of the others. We illustrate the application of CFA by devising a spectrally-based hierarchically decoupled feature set and applying it to obtain different types of image synthesis that are not achievable using traditional (coupled) feature sets.
ICASSP 2020 - 2020 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 2020
We introduce a formalism that justifies and extends a heuristic method for algebraically decoupli... more We introduce a formalism that justifies and extends a heuristic method for algebraically decoupling deterministic features that recently proved useful for improving feature-based classification. Our new formalism is based on defining transformations inside manifolds, by following trajectories along the features' gradients. Through these transformations we define a normalization that, we demonstrate, allows for decoupling differentiable features. By applying this to sampling moments, we obtain a quasi-analytic solution for the orthokurtosis, a modification of the kurtosis that is not just decoupled from mean and variance, but also from skewness. After theoretically motivating feature decoupling for random data distributions, we illustrate with a regression problem example how decoupled features may perform significantly better than coupled ones.
Imaging and Applied Optics 2019 (COSI, IS, MATH, pcAOP), 2019
Proceedings Imaging and Applied Optics 2019, Munich, Germany, 24–27 June 201
Computational Optics II, 2018
Aspheres in optical design are frequently used to achieve high optical performance in imaging app... more Aspheres in optical design are frequently used to achieve high optical performance in imaging applications. However, manufacturing aspheres involves serious precision and cost issues that must be considered. We show that, by applying a hybrid digital-optical design approach, the amount of the asphericity cost in a single surface may be significantly alleviated without compromising the performance. First, we compute the amount of spherical aberration depending on the optical parameters (conic constant and shape factor), and compute its corresponding point spread function (PSF). From the PSF and the spectral distribution of clean images and noise, we set a statistical observation model for estimating the expected image quality (in mean square error terms) in the image sensor and also in the digitally restored image. In addition, we use a previously proposed metric for quantifying the asphere fabrication cost, to set different cost scenarios. For each of these scenarios, we study how image quality is optimized, before and after digital restoration. Reversely, we find the optical configurations of minimal asphericity cost amongst those providing a very low aberration level. Although here we have limited our study to just on-axis, monochromatic imaging, we show in simulations how our digital-optical combined approach has a high potential for boosting the cost-effectiveness trade-off.
Journal of Modern Optics, 2020
The Point-Spread-Function (PSF) field characterizes the geometric and diffractive properties of m... more The Point-Spread-Function (PSF) field characterizes the geometric and diffractive properties of most optical system designs for imaging applications. The conventional method of computing the PSF field is carried out in two steps: first, geometrical computation of the wave aberration function, and then, diffraction evaluation. That method usually applies two approximations: 1) the exit and entrance pupil ray intersection coordinates are equal; and 2) the optical field amplitude distribution does not change between exit and entrance pupil planes. We propose here a variation of the conventional method that allows overcoming these two approximations in axially symmetric optical systems. To show the potentials of the method we applied it to a Cooke triplet. We analyze the influence of the number of traced rays on the measured accuracy of the method. We also evaluate the differences in the PSF estimation accuracy with respect to a method where the two aforementioned approximations were used.
2017 IEEE International Conference on Image Processing (ICIP), 2017
In recent years, boundary problems associated to image restoration have attracted the attention o... more In recent years, boundary problems associated to image restoration have attracted the attention of imaging scientists. We explore here the scenario of arbitrary boundary shapes (exemplified by blurred-background images), starting from a general discussion and advancing towards realist conditions, with simulations and real photographic images. We describe our Spectral-Pre-Adaptation (SPA) method, and compare it to the highly successful unconstrained boundary conditions Alternating Direction Method of Multipliers (UBC ADMM) method. Preliminary results indicate that SPA, combined with highly efficient restoration algorithms, such as Constrained Dynamic (ConDy) L2-relaxed L0, may set the new state-ofthe-art (in performance and computational efficiency) for this kind of problems.
Optical Design and Fabrication 2017 (Freeform, IODC, OFT), 2017
2006 14th European Signal Processing Conference, 2006
We present a generic Bayesian framework for signal estimation that incorporates into the cost fun... more We present a generic Bayesian framework for signal estimation that incorporates into the cost function a perceptual metric. We apply this framework to image denoising, considering additive noise of known density. Under certain assumptions on the way local differences in visual responses add up into a global perceptual distance, we obtain analytical solutions that exhibit interesting theoretical properties. We demonstrate through simulations, using an infomax nonlinear perceptual mapping of the input and a local Gaussian model, that in the absence of a prior the new solutions provide a significant improvement on the visual quality of the estimation. Furthermore, they also improve in Mean Square Error terms w.r.t. their non-perceptual counterparts.
Journal of the Optical Society of America A, 2017
We present a comprehensive procedure to simulate real-world scenes viewed through ophthalmic lens... more We present a comprehensive procedure to simulate real-world scenes viewed through ophthalmic lenses. Such method enables to anticipate the effects on image formation of combined undesired optical defects typically found in ophthalmic lenses: blur, distortion and chromatic aberration. Additionally, it helps comparing the expected scenes seen with different lens designs. The procedure is based on the following steps: 1) To calculate distortion and local dioptric matrix associated to a set of different gaze directions; 2) To estimate point-spread-functions (PSF) associated to these matrices; 3) To compute the joint action of distortion, chromatic aberration and PSF field on the scenes. We illustrate this procedure with two +5 D spherical lenses: a moderately good performance lens and a highly degradating one. The method is suitable to evaluate ophthalmic lenses in a virtual reality framework.
ACM Transactions on Graphics, 2016
We propose a method to simulate the rich, scale-dependent dynamics of water waves. Our method pre... more We propose a method to simulate the rich, scale-dependent dynamics of water waves. Our method preserves the dispersion properties of real waves, yet it supports interactions with obstacles and is computationally efficient. Fundamentally, it computes wave accelerations by way of applying a dispersion kernel as a spatially variant filter, which we are able to compute efficiently using two core technical contributions. First, we design novel, accurate, and compact pyramid kernels which compensate for low-frequency truncation errors. Second, we design a shadowed convolution operation that efficiently accounts for obstacle interactions by modulating the application of the dispersion kernel. We demonstrate a wide range of behaviors, which include capillary waves, gravity waves, and interactions with static and dynamic obstacles, all from within a single simulation.
Ophthalmic and Physiological Optics, 2016
This paper introduces a new texture synthesis-by-analysis method, applying a visual-based approac... more This paper introduces a new texture synthesis-by-analysis method, applying a visual-based approach which has some important advantages over more traditional texture modeling and synthesis techniques. The basis of the method is to encode the textural information by sampling both the power spectrum and the histogram of homogeneously textured images. The spectrum is sampled in a log-polar grid by using a pyramid Gabor scheme. The input image is split into a set of 16 Gabor channels (using four spatial frequency levels and four orientations), plus a low-pass residual (LPR). The energy and equivalent bandwidths of each channel, as well as the LPR power spectrum and the histogram, are measured and the latter two are compressed. The synthesis process consists of generating 16 Gabor filtered independent noise signals with spectral centers equal to those of the Gabor filters, whose energy and equivalent bandwidths are calculated in order to reproduce the measured values. These band-pass sign...
IEEE International Conference on Image Processing 2005, 2005
We describe an adaptive denoising method for images decomposed in overcomplete oriented pyramids.... more We describe an adaptive denoising method for images decomposed in overcomplete oriented pyramids. Our approach integrates two kinds of adaptation: 1) a 'coarse' adaptation, where a large window is used within each subband to estimate the local signal covariance; 2) a 'fine' adaptation, which uses small neighborhoods of coefficients modelled as the product of a Gaussian and a hidden multiplier, i.e., as Gaussian scale mixtures (GSM). The former provides adaptation to local spectral features, whereas the latter adapts to local energy fluctuations. We formulate our method as a Bayes Least Squares estimator using spatially variant GSMs. We also discuss the importance of image representation, compare the results using two different representations with complementary features, and study the effect of merging their results. We demonstrate through simulation that our method surpasses the state-of-the-art performance, in a L 2-norm sense.
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Papers by Javier Portilla