Adaptive exposure estimation for high dynamic range imaging applied to natural scenes and daylight skies

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 dynamic range of a scene with high dynamic range (HDR) content. The proposed method is adaptive to scene content and to any camera response and configuration, and it works on-line since the exposure times are estimated as the capturing process is ongoing. Besides, it requires no a priori information about scene content or radiance values. The resulting bracketing sets are minimal in the default method settings, but the user can set a tolerance for the maximum percentage of pixel population that is underexposed or saturated, which allows for a higher number of shots if a better signal-to-noise ratio (SNR) in the HDR scene is desired. This method is based on the use of the camera response function that is needed for building the HDR radiance map by stitching together several differently exposed low dynamic range images of the scene. The use of HDR imaging techniques converts our digital camera into a tool for measuring the relative radiance outgoing from each point of the scene, and for each color channel. This is important for accurate characterization of optical phenomena present in the atmosphere while not suffering any loss of information due to its HDR.We have compared our method with the most similar one developed so far [IEEE Trans. Image Process. 17, 1864 (2008)]. Results of the experiments carried out for 30 natural scenes show that our proposed method equals or outperforms the previously developed best approach, with less shots and shorter exposure times, thereby asserting the advantage of being adaptive to scene content for exposure time estimation. As we can also tune the balance between capturing time and the SNR in our method, we have compared its SNR performance against that of Barakat’s method as well as against a ground-truth HDR image of maximum SNR. Results confirm the success of the proposed method in exploiting its tunability to achieve the desired balance of total Δt and SNR

Colorimetric and spectral data analysis of consolidants used for preservation of medieval plasterwork

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 changes produced by consolidation treatments applied on polychromed plasterwork. Thus, for this investigation we used a total of 18 plaster test specimens which reproduce the techniques and materials present in plasterwork from the medieval era, on which a selection of six currently-used consolidants was applied. By doing this, we have proved that the use of this method over traditional colorimetry has several advantages, such as the analysis of spatial homogeneity or obtaining colorimetric data of the entire scanned surface.Ministry of Economy andCompetitiveness and by the European Regional Development Fund(MINECO/ERDF, EU) within the framework of the Research ProjectHAR2015-66139-P, as well as by the Excellence Project of theAndalusian Regional Government P12-HUM-1941

Eight-Channel Multispectral Image Database for Saliency Prediction

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 experimental study of such models based on spectral images is difficult because of the lack of available data to work with. This article presents the first eight-channel multispectral image database of outdoor urban scenes together with their gaze data recorded using an eyetracker over several observers performing different visualization tasks. Besides, the information from this database is used to study whether the complexity of the images has an impact on the saliency maps retrieved from the observers. Results show that more complex images do not correlate with higher differences in the saliency maps obtained.Spanish Ministry of Science, Innovation, and Universities (MICINN) RTI2018-094738-B-I00European Commissio

Spectral Filter Selection for Increasing Chromatic Diversity in CVD Subjects

We are grateful to Angela Tate for revising the English text. We are also grateful to the reviewers for their insightful suggestions.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 have carried out simulations performed using the spectral reflectances captured either by a hyperspectral camera or by a spectrometer. We have also studied the effects of these filters on color coordinates. Finally, we have simulated the results of two widely used color blindness tests: Ishihara and Farnsworth–Munsell 100 Hue (FM100). In these analyses the selected filters are compared with the commercial filters from EnChroma and VINO companies. The results show that the increase in NODC with the selected filters is not relevant. The simulation results show that none of these chosen filters help color vision deficiency (CVD) subjects to pass the set of color blindness tests studied. These results obtained using standard colorimetry support the hypothesis that the use of color filters does not cause CVDs to have a perception similar to that of a normal observer.This research was supported by the Spanish State Agency for Research (AEI) and the Ministry for Economy, Industry and Competitiveness (MIMECO) by means of grant number FIS2017-89258-P with European Union FEDER (European Regional Development Funds) support, and by the Spanish Ministry of Science, Innovation, and Universities, with support from the European Regional Development Funds under grant number RTI2018-094738-B-I00

¿Realmente existe convergencia regional en México? Un modelo no lineal de datos panel TAR

This paper analyzes the hypothesis of regional convergence in Mexico for the period 1970-201 through a non-linear growth model. The methodology combines three approaches: the panel-data threshold autoregressive (TAR) model, the unit root tests in panel and the computation of the critical values by bootstrapping simulation. The empirical results of the nonlinear model applied to the per capita GDP of different groups of States in Mexico suggest that the proposed model is superior to the linear model and show evidence of partial and absolute convergence for the group of the eleven “richer” States in certain sub-periods. Surprisingly, considering the average of the eleven richer and combining it with the rest of the States convergence evidence was found. Furthermore, when all the States are compared, the hypothesis of divergence could not be rejected. These results show that convergence is present in groups of States with similar characteristics and specific periods, which reinforces the idea that there are convergence “clubs” in Mexico

Evaluation of Cleaning Processes Using Colorimetric and Spectral Data for the Removal of Layers of Limewash from Medieval Plasterwork

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 cleaning technique best preserves the original appearance of the colored plaster. Different pigments found below the lime layer may behave differently depending on the cleaning technique used. Usually, colorimetric or photometric area-based measurements are carried out to study the color of the cleaned areas to compare with their original color, obtained from pre-made plaster probes. However, this methodology fails when the mean color difference is not enough to fully characterize the changes in texture and color appearance. This study presents a set of experiments carried out using two different pigments (cinnabar and malachite) covered with lime, and treated with nine different cleaning techniques on plaster probes prepared according to medieval techniques. We have studied the effect of the cleaning process on the color and the homogeneity of the samples using a hyperspectral imaging workflow. Four different analysis methods are presented and discussed. Our results show that the proposed analysis is able to provide a much more comprehensive and diversified characterization of the quality of the cleaning method compared to the commonly used colorimetric or photometric area-based measurements.Ministry of Economy and Competitiveness HAR2015-66139-PEuropean Union (EU) HAR2015-66139-

¿Realmente existe convergencia regional en México? Un modelo no lineal de datos panel TAR

This paper analyzes the hypothesis of regional convergence in Mexico for the period 1970-201 through a non-linear growth model. The methodology combines three approaches: the panel-data threshold autoregressive (TAR) model, the unit root tests in panel and the computation of the critical values by bootstrapping simulation. The empirical results of the nonlinear model applied to the per capita GDP of different groups of States in Mexico suggest that the proposed model is superior to the linear model and show evidence of partial and absolute convergence for the group of the eleven “richer” States in certain sub-periods. Surprisingly, considering the average of the eleven richer and combining it with the rest of the States convergence evidence was found. Furthermore, when all the States are compared, the hypothesis of divergence could not be rejected. These results show that convergence is present in groups of States with similar characteristics and specific periods, which reinforces the idea that there are convergence “clubs” in Mexico

Short-term effects of text-background color combinations on the dynamics of the accommodative response

The purpose of the present study was to assess the accommodative response and pupillary dynamics while reading passages with different text-background color combinations on an LCD screen. Twenty healthy young adults read fourteen 2-min passages designed with fourteen different color combinations between text and background, while the accommodative and pupil responses were continuously measured with a binocular open-field autorefractometer. Our results revealed that the text-background color combination modulates the accommodative and pupillary dynamics during a 2-minutes reading task. The blue-red combination induced a heightened accommodative response, whereas positive polarities were associated with more variability of the accommodative response and smaller pupil sizes. Participants reported lower perceived ratings of legibility for text-background color combination with lower luminance contrast (white-yellow). The manipulation of text-background color did not have a significant effect on reading speed. These results may have important applications in the design of digital visual interfaces.This research was supported by the Spanish Ministry of Science, Innovation and Universities, with support from European Regional Development Fund (ERDF), RTI2018-094738-B-I00 project

Spectral information to get beyond color in the analysis of water‑soluble varnish degradation

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 characterize the spatial and color inhomogeneity across pixels, showing that the pixel spectral data are critical for an accurate characterization of the degradation process of the varnishes. Since the varnishes typically become yellower with ageing, this study introduces two novel and simple-to-compute yellowness indices based on the spectral information, which are validated against a standard colorimetric index (ASTM-E313 2015). The potential uses of spectral information are demonstrated with several pieces of a real antique map sample by comparing the spectral information measured before and after cleaning the sample. To sum up, the main contributions of this study are the characterization of the spatial homogeneity through pixel-based spectral and color information and the proposal of spectral-based yellowing indices for two critical applications (ageing process follow-up and effect of cleaning), as demonstrated with synthetic and historical samples of varnished paper respectively.Spanish Ministry of Economy and Competitiveness, under research Grant DPI2015-64571-R. Spanish State Agency of Research (AEI) and the Ministry for Economy, Industry and Competitiveness (MIMECO) by means of the Grant Number FIS2017-89258-P with European Union FEDER (European Regional Development Funds) support