E. M. Valero

• PhD
• Professor (Associate) at University of Granada

The cleaning of re-polychromated plaster is a rather challenging task for Conservators. The optimal choice of solvents and its application instruments may depend on the original polychromy (binder and pigment) that aims to be revealed and the overlay polychromy (binder and pigment) as well. We present a new image-processing based method that uses h...

In this study, we present an analysis of dehazing techniques for hyperspectral images in outdoor scenes. The aim of our research is to compare different dehazing approaches for hyperspectral images and introduce a new hyperspectral image database called GRANHHADA (GRANada Hyperspectral HAzy Database) containing 35 scenes with various haze condition...

Hyperspectral imaging has recently consolidated as a useful technique for pigment mapping and identification, although it is commonly supported by additional non-invasive analytical methods. Since it is relatively rare to find pure pigments in aged paintings, spectral unmixing can be helpful in facilitating pigment identification if suitable mixing...

Hyperspectral imaging has been increasingly used for non-destructive analysis of historical documents. Spectral reflectance data allow material identification and mapping using a library of reference spectra. Similarity metrics are crucial for quantifying the differences between reference and test spectra. Despite the apparent simplicity of the met...

Three endmember extraction methods (NFINDR, NMF and manual extraction) are compared in two stages (pre- and post- intervention) of the same painting, a Maternity on copper plate, under study for the formulation of a hypothesis on the authorship and the dating. The endmembers are extracted from spectral images in the 400-1000 nm range. The main aim...

Approximately 8% of Caucasian males and 0.5% of females have congenital red-green color vision deficiencies (CVD), and a number of eye diseases are accompanied by acquired CVD. This feature issue includes ten contributions regarding existing and proposed algorithms and devices intended to help CVD subjects compensate for their color deficiencies. I...

Color vision deficiency (CVD) has gained in relevance in the last decade, with a surge of proposals for aid systems that aim to improve the color discrimination capabilities of CVD subjects. This paper focuses on the proposal of a new metric called CVD-MET, that can evaluate the efficiency and naturalness of these systems through a set of images us...

The use of blue-blocking filters is increasing in spectacle lens users. Despite the low absorption in the blue range, some users complain about these filters because they affect their color perception. In a pilot study we have evaluated how the long-term use of 8 different blue-blocking filters impact the color perception during more than 2 weeks o...

There is a belief that observers with color vision deficiencies (CVD) perform better in detecting camouflaged objects than normal observers. Some studies have concluded contradictory findings when studying the performance of normal and CVD observers in the camouflage detection tasks in different conditions. This work presents a literature review on...

Images captured under bad weather conditions (e.g., fog, haze, mist, dust, etc.), suffer from poor contrast and visibility, and color distortions. The severity of this degradation depends on the distance, the density of the atmospheric particles and the wavelength. We analyzed eight single image dehazing algorithms representative of different strat...

Indigo blue is a natural organic color from the Indigofera tinctoria plant. It is insoluble in water and does not require mordant to fix the color; therefore, due to its nature it can be considered as a pigment or dye. The identification of indigo in cultural heritage is very difficult due to the complexity of its chemical formula and the changes t...

Saliency prediction is a very important and challenging task within the computer vision community. Many models exist that try to predict the salient regions on a scene from its RGB image values. Several new models are developed, and spectral imaging techniques may potentially overcome the limitations found when using RGB images. However, the experi...

In the cultural heritage preservation of medieval buildings, it is common to find plaster walls covered in lime, which previously were painted in polychromy. The conservation interventions usually try to remove the whitewash, whilst maintaining the original color of the painted wall as much as possible. However, there is no agreement on which clean...

In foggy or hazy conditions, images are degraded due to the scattering and attenuation of atmospheric particles, reducing the contrast and visibility and changing the color. This degradation depends on the distance, the density of the atmospheric particles and the wavelength. We have tested and applied five single image dehazing algorithms, origina...

Under fog or haze images are degraded due to scattering and attenuation of atmospheric particles, reducing the contrast and visibility and changing the color. This degradation depends on the distance, the density of atmospheric particles and on the wavelength. Are single image dehazing algorithms able to deal with spectral images? Would they better...

The idea of correcting Color Vision Deficiencies (CVD) through color filters goes back to 1837, with the paper of Seebeck [1]. Later on, Maxwell [2] designed a pair of spectacles for red-green CVD in 1857. Since then, many papers have dealt with this idea of enriching the vison of CVD subjects by passive and active helps. In the last times, several...

In the last 2 decades, there has been a resurgence of the idea that passive aids such as colour filters can be an effective solution to compensate colour vision deficiency (CVD) or improve colour vision for subjects with CVD. We examine briefly the scientific evidence that has to date been gathered to study the reliability of these aids. In the lig...

Recently Karepov and Ellenbogen [Opt. Lett. 45, 1379 (2020)OPLEDP0146-959210.1364/OL.384970] claimed that a new metasurface-based contact lens is able to correct deuteranomaly. Unfortunately, their results are not supported by psychophysical experiments, and some key assumptions in their simulations were misinterpreted. All of this has led to wrong...

This paper analyzes, through computational simulations, which spectral filters increase the number of discernible colors (NODC) of subjects with normal color vision, as well as red–green anomalous trichromats and dichromats. The filters are selected from a set of filters in which we have modeled spectral transmittances. With the selected filters we...

Abstract Spectral images were captured of paper samples varnished with two water-soluble materials: gum arabic and egg white. The samples were submitted to degradation processes that partially or totally eliminated the varnish from the substrate (water immersion and ageing). The spectral information was used to obtain average color data and to char...

A pesar de que la visión defectiva del color afecta al 8% de los hombres y al 0,5% de las mujeres caucásicas, todavía no existe un tratamiento eficaz para la misma, aunque la terapia genética se haya probado con éxito en primates adultos [1]. Las ayudas para mejorar la visión del color en sujetos con CVD (Color Vision Deficiency) se clasifican en d...

A pesar de que la visión defectiva del color afecta al 8% de los hombres y al 0,5% de las mujeres caucásicas, todavía no existe un tratamiento eficaz para la misma, aunque la terapia genética se haya probado con éxito en primates adultos [1]. Las ayudas para mejorar la visión del color en sujetos con CVD (Color Vision Deficiency) se clasifican en d...

The incorporation of new methods of heritage analysis belonging to other branches of science is currently providing very useful tools for the examination of preservation products. This paper outlines the use of spectral images as an alternative to traditional colorimetry measurements carried out with a spectrophotometer for the evaluation of color...

Saliency detection has been an important topic during the last decade. The main goal of saliency detection models is to detect the most relevant objects in a given scene. Most of these models use RGB (Red, Green, Blue) images as an input because they mainly focus on applications where features (eg, faces, textures, colors, or human silhouettes) are...

In our ongoing research on the effectiveness of different passive tools for aiding Color Vision Deficiency (CVD) subjects, we have analyzed the VINO 02 Amp Oxy-Iso glasses using two strategies: 1) 52 observers were studied using four color tests (recognition, arrangement, discrimination, and color-naming); 2) the spectral transmittance of the lense...

Hyperspectral imaging of effect coated samples can be challenging, mainly because of the large differences in irradiance that stem from the orientation distribution of the metallic flakes contained in the coating, and from the lightness variations from one sample to another. Besides, high spatial resolution is needed to sample the details of the te...

This paper presents a complete framework for capturing and processing hyperspectral reflectance images of artworks in situ, using a hyperspectral line scanner. These capturing systems are commonly used in laboratory conditions synchronized with scanning stages specifically designed for planar surfaces. However, when the intended application domain...

Medieval plasterwork’s preservation is compromised as the lack of cohesion between polychrome sections, if not adequately treated, causes the irretrievable loss of its original appearance. It is common to observe only scarce remains of the plasterwork’s original color appearance in monuments like the Alhambra in Granada, or the Alcazar in Seville....

The commercialization of EnChroma glasses has generated great expectations for people to be able to see new colors or even correct color vision deficiency (CVD). We evaluate the effectiveness of these glasses using two complementary strategies for the first time. The first consists of using the three classical types of tests — recognition, arrangem...

Cultural heritage objects consist among others, in a wide variety of paper graphics such as maps [1], paintings imitations [2], etc. It is the work of conservators, to preserve these old samples in a good condition. One of the key factors is to preserve their original aspect as much as the conservation techniques allow to, still giving more importa...

En imágenes multimodales, el registro es más complejo por la diferencia de ángulo de visión e intensidad existente en cada uno de los píxeles de las imágenes. En este trabajo se estudia el registro de imágenes multimodales, obtenidas por un sistema con diferentes dispositivos multiespectrales e hiperespectrales, para el reconocimiento de objetos e...

We propose a method for the capture of high dynamic range (HDR), multispectral (MS), polarimetric (Pol) images of indoor scenes using a liquid crystal tunable filter (LCTF). We have included the adaptive exposure estimation (AEE) method to fully automatize the capturing process. We also propose a pre-processing method which can be applied for the r...

A framework for registration of multi-channel image data from a desktop line-scan multi-spectral camera system is presented. For this rather novel imaging technology, the source of image misalignment is distinct from other multi-spectral imaging approaches. The authors illustrate this by empirical analysis of channel misalignment from image data of...

Condition 400 – 720 nm with 5 nm intervals 1. Before brushing (the teeth hadn't been brushed for 24 hours) 2. With a plaque disclosing agent liquid 3. After brushing Equipment • LCTF (Varispec VIS 10-20, Perkin Elmer) • Monochrome camera (Retiga SRV, QImaging) Registration In order to alleviate displacements due to an observer's movement, a feature...

1. Introducción Recientemente se han empezado a comercializar diferentes modelos de gafas de la compañía americana EnChroma ® (http://enchroma.com) bajo la denominación " Color for the Color Blind TM ". La compañía fue fundada en 2010 y la primera versión de gafas se lanzó en 2012, apareciendo en 2014 una versión mejorada. Actualmente hay disponibl...

Some years ago, glasses that simulate anomalous color vision conditions were commercially available for the first time. Recently, a company started to market glasses that enhance vision for color deficient people. Both kinds of glasses make use of spectral filters in their quest to achieve the mentioned goals, but there are very few scientific stud...

There are several imaging techniques designed and developed to overcome the limitations of common imaging systems. Each of these techniques, such as multispectral imaging, high dynamic range imaging or polarimetric imaging suppose a challenge individually. The drawbacks are even more when we try to combine them into a single capturing system o meth...

Limitations of conventional RGB cameras with respect to color and spectral measurements are widely known and motivated the development of multi-spectral camera systems, which extend the amount of spectral information captured from an imaging scene. With the camera response data captured by such a system, machine learning techniques can be used to r...

Digital imaging of common scenes can be a very challenging task if the scene radiances present a high dynamic range (HDR). HDR imaging techniques are applied to overcome this issue. The most popular technique is based in the combination of differently exposed low dynamic range (LDR) images. However there is a lack of a robust method for determining...

The acquisition of spectral reflectance factor image data in an outdoor environment is a challenging task, mostly due to nonstatic scene content and illumination. In this work, we propose a work-flow for this task using a commercial Bragg-grating-based hyperspectral imager that can capture the visible and near-infrared part of the light spectrum. T...

Digital imaging of natural scenes and optical phenomena present on them (such as shadows, twilights, and crepuscular rays) can be a very challenging task because of the range spanned by the radiances impinging on the capture system. We propose a novel method for estimating the set of exposure times (bracketing set) needed to capture the full dynami...

In this work we will address two of the main characteristics of visual coding: the spectral codification (either in a sensor or the human retina with the spectral information being lost), and the subsequent color coding and perception (which in the HVS is linked to high visual areas and allows full color perception without having knowledge about th...

Density measurement of printed color samples takes an important role in print quality inspection and process control. When multi-spectral imaging systems are considered for surface reflectance measurement, the possibility of calculating spectral print density over the spatial image domain arises. A drawback in using multi-spectral imaging systems i...

In spectral imaging, spatial and spectral information of an image scene are combined. There exist several technologies that allow the acquisition of this kind of data. Depending on the optical components used in the spectral imaging systems, misalignment between image channels can occur. Further, the projection of some systems deviates from that of...

This work focuses on the improvement of a multispectral imaging sensor based on transverse field detectors (TFDs). We aimed to achieve a higher color and spectral accuracy in the estimation of spectral reflectances from sensor responses. Such an improvement was done by combining these recently developed silicon-based sensors with color filter array...

Abstract. A multispectral acquisition system to examine the bidirectional reflectance distribution function of structurally colored biological materials in the visible range is presented. We focus on the purple-blue and white-pearl wing scales of the male butterfly Sasakia charonda. Multispectral imaging was done by changing the illumination angula...

In this work, we evaluate the conditionally positive definite logarithmic kernel in kernel-based estimation of reflectance spectra. Reflectance spectra are estimated from responses of a 12-channel multispectral imaging system. We demonstrate the performance of the logarithmic kernel in comparison with the linear and Gaussian kernel using simulated...

We have analyzed the performance of simulated multispectral systems for the spectral recovery of reflec-tance of printer inks from camera responses, including noise. To estimate reflectance we compared the perform-ance of four algorithms which were not comparatively tested using the same data sets before. The criteria for selection of the algorithm...

The performance of learning-based spectral estimation is greatly influenced by the set of training samples selected to create the reconstruction model. Training sample selection schemes can be categorized into global and local approaches. Most of the previously proposed global training schemes aim to reduce the number of training samples, or a sele...

In this paper, we implemented and compared two approaches for colour image segmentation of natural scenes: one is finding the best colour space for colour-based segmentation, and the other is segmenting by using the spectral data obtained by estimation from sensor responses. Results show that using estimated spectral data for colour image segmentat...

Transverse Field Detector (TFD) sensors are tunable, full spatial resolution, color sensors, currently still under development (Langfelder 2009). One of their main advantages over common imaging systems is that their spectral sensitivities can be modulated by applied voltage and also that they can achieve full spatial resolution by exploiting the w...

The optical transfer function (OTF) and its modulus, the modulation transfer function (MTF), are widely accepted measurements of the quality of optical systems. There are different ways of estimating both OTF and MTF. Random-dot-pattern methods have some advantages when computing MTFs, especially those which present the pattern on a liquid crystal-...

Erythema is a common visual sign of gingivitis. In this work, a new and simple low-cost image capture and analysis method for erythema assessment is proposed. The method is based on digital still images of gingivae and applied on a pixel-by-pixel basis. Multispectral images are acquired with a conventional digital camera and multiplexed LED illumin...

La imagen multiespectral extrae información espectral para cada pixel de una imagen. El rango de posibles aplicaciones es muy amplio. Se han dedicado muchos esfuerzos para conseguir resolución espacial y espectral completa con un solo sensor, ofreciendo una respuesta rápida y precisa [1]. Los sensores TFD (Transverse Field Detectors) [2],[3] tienen...

Gingival health state assessment has always been consid-ered of great importance in the field of dentistry. A major con-cern in this area is the subjectivity that commonly applied as-sessment methods inherit. Most of the previous approaches that aim at introducing objectivity in the assessment are based on data from photographic images of the gingi...

Albedo estimation has traditionally been used to make compu-tational simulations of real objects under different conditions, but as yet no device is capable of measuring albedo directly. The aim of this work is to introduce a photometric-based color imaging framework that can estimate albedo and can reproduce the appearance both indoors and outdoor...

We have modified the Fuzzy C-Means algorithm for an application related to segmentation of hyperspectral images. Classical fuzzy c-means algorithm uses Euclidean distance for computing sample membership to each cluster. We have introduced a different distance metric, Spectral Similarity Value (SSV), in order to have a more convenient similarity mea...

The main aim of this study is to investigate which would be the best algorithm for spectral estimation from Transverse Field Detectors (TFD) sensor responses. We perform a quality check of the estimation accuracy of five different algorithms, most of which are recent proposals. Some modifications are introduced as well in their implementation to si...

We have developed a psychophysical experiment for testing the influence of color in the development of architectural projects. The main building properties analyzed were the length, the size and the depth cues. A real architectural project was used as a standard reference to design a psychophysical experiment with naïve and non-naïve. Results show...

We made a computational simulation of spectral recovery system for printer inks, based on different sensor sets and spectral estimation algorithms. We additionally performed an exhaustive search for the best group of sensors in order to improve the performance of the multispectral system. The result showed the algorithms based on neural networks do...

In this paper we outline our current research topics related with the field of multispectral science. We describe the last developments in the field of spectral estimation (spectral recovery) from few sensors, mainly in the field of natural and artificial illuminants. color, spectral, multispectral, sensors, illuminants, recovery I. INTRODUCTION Ou...

Resumen: El campo de las imágenes multiespectrales o hiperespectrales está registrando una considerable actividad en los últimos años. Los algoritmos de Clustering se han aplicado en este contexto con el fin principalmente de clasificar materiales u objetos incluidos en las escenas multiespectrales (ya sean provenientes de sistemas de captura de im...

This paper proposes a spatio-spectral imaging device to simulate and acquire color images under different geometries of illumination. The method allows image analysis and synthesis, even for rough-textured surfaces, under different directions of the incident illumination. In addition the use of the albedo instead of directly the RGB information hel...

Clustering techniques have been applied to spectral images mostly to classify materials or objects included in the scenes. We present in this study new data concerning the use of clustering algorithms as a pre-processing step for obtaining spectral data from camera responses. Four different clustering algorithms have been used, and the Kohonen maps...

Photometric-stereo techniques are based on the fact that image intensity depends upon the orientation of the surface with regard to the source of the illumination and its spectral reflectance. They are of special interest when dealing with rough surfaces because they usually present shadowed regions where sudden illumination changes might be found....

Compact discs are a useful tool for studying interference and diffraction. We propose an easy and inexpensive experiment to distinguish between replicated and duplicated compact discs based on Fraunhofer diffraction. The nonvisible differences of the surface of compact discs depend on the way that they have been manufactured and can be seen by usin...

A linear pseudo-inverse method for unsupervised illuminant recovery from natural scenes is presented. The algorithm, which uses a digital RGB camera, selects the naturally occurring bright areas (not necessarily the white ones) in natural images and converts the RGB digital counts directly into the spectral power distribution of the illuminants usi...

Spectral imaging can provide spectral information from which spectral radiance or reflectance can be recovered at each image pixel. Recovery algorithms lead to good spectral and colorimetric performance by directly transforming RGB digital counts to spectral reflectances, but his approach is sensitive to the size and composition of the training set...

Reflectance estimation from RGB data in natural scenes is studied computationally including the use of different unsupervised classification techniques to divide the RGB data into a number of subgroups with similar characteristics to test if these techniques lead to any improvements in the quality of the spectral signals obtained. The direct pseudo...

Many spectral-recovery methods using RGB digital cameras assume the underlying smoothness of illuminant and reflectance spectra, and apply low-dimensional linear models. The aim of the present work was to test whether a direct-mapping method could be used instead of a linear-models approach to recover spectral radiances and reflectances from natura...

The aim of a multispectral system is to recover a spectral function at each image pixel, but when a scene is digitally imaged under a light of unknown spectral power distribution (SPD), the image pixels give incomplete information about the spectral reflectances of objects in the scene. We have analyzed how accurately the spectra of artificial fluo...

In a previous work [ Appl. Opt. 44, 5688 (2005) ] we found the optimum sensors for a planned multispectral system for measuring skylight in the presence of noise by adapting a linear spectral recovery algorithm proposed by Maloney and Wandell [ J. Opt. Soc. Am. A 3, 29 (1986) ]. Here we continue along these lines by simulating the responses of thre...

Previous authors (J Opt Soc Am A 2000; 17: 1952–1961; J Opt Soc Am A 2001; 18: 253–264) have proposed a pixel-by-pixel image descriptor that is invariant to certain changes in illumination. We have studied the possibility of applying such an invariant descriptor to scenery illuminated by natural light, by choosing sensors that allow the invariant t...