Adolfo Molada Tebar - Academia.edu (original) (raw)

Proceedings by Adolfo Molada Tebar

Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci., Feb 25, 2022

Graffiti is a short-lived form of heritage balancing between tangible and intangible, offensive a... more Graffiti is a short-lived form of heritage balancing between tangible and intangible, offensive and pleasant. Graffiti makes people laugh, wonder, angry, think. These conflicting traits are all present along Vienna's Donaukanal (Eng. Danube Canal), a recreational hotspot – located in the city's heart – famous for its endless display of graffiti. The graffiti-focused heritage science project INDIGO aims to build the basis to systematically document, monitor, and analyse circa 13 km of Donaukanal graffiti in the next decade. The first part of this paper details INDIGO's goals and overarching methodological framework, simultaneously placing it into the broader landscape of graffiti research. The second part of the text concentrates on INDIGO's graffiti documentation activities. Given the project's aim to create a spatially, spectrally, and temporally accurate record of all possible mark-makings attached in (il)legal ways to the public urban surfaces of the Donaukanal, it seems appropriate to provide insights on the photographic plus image-based modelling activities that form the foundation of INDIGO's graffiti recording strategy. The text ends with some envisioned strategies to streamline image acquisition and process the anticipated hundreds of thousands of images.

Papers by Adolfo Molada Tebar

Zenodo (CERN European Organization for Nuclear Research), May 11, 2023

Colour is a powerful communication element in most forms of cultural heritage. This importance of... more Colour is a powerful communication element in most forms of cultural heritage. This importance of colour notwithstanding, the documentation of cultural heritage typically captures the geometrical aspects and seldom the spectral dimensions of an artefact. This is partly because the science of colour (called colorimetry) is non-trivial. In addition, capturing accurate colour data with digital cameras remains challenging due to the operating principle of standard imaging sensors and the need for a stable and well-characterised illumination source. Despite these limitations, the heritage science project INDIGO made it one of its central aims to generate colour-accurate photos from graffiti captured with standard digital cameras in varying outdoor illumination conditions. This paper first discusses the importance of colour accuracy in graffiti documentation. Afterwards, the text details (in a non-mathematical manner) essential colorimetric and camera principles that underlie the generation of colour images from raw image sensor data. This in-depth coverage supports clarifying the main hurdles to accurate photo colours. Finally, the paper introduces the open-source COOLPI software resulting from this research. We are confident that COOLPI will benefit any other heritage documentation project, or any application where digital cameras play a fundamental role in acquiring correct colour values.

We could live in black and white, but fortunately, life is in color. Color is a source of emotion... more We could live in black and white, but fortunately, life is in color. Color is a source of emotion, of memories, of sensations. Color makes us happy. It's the same with people. Like colors, there are people who calm you down, evoke memories, embrace you, smile at you. My gratitude goes first of all to these people, who, like colors, have brought fullness to my life. Especially, to my parents, my sister and my friends, who have always been there, and will always be. During my PhD, I had to go through moments of light and darkness. It has been a long, hard road, but it was worth it. I have learned a lot. Thank you, José Luis andÁngel, for guiding me through these years. Your contributions have been essential in bringing color to this thesis. Thanks also to a simple email. An email that changed my life. Thank you Stephen for responding positively to my request, and allowing me to take six amazing months in Leeds (UK), collaborating in the Colour Research Group at the School of Design. A dream come true! Thanks also to Zeynep, for the month stay at Mimar Sinan Fine Arts University (Istanbul, Turkey). I enjoyed the amazing sights and monuments. When I think of Istanbul, I remember colors. Thanks to all of you! Finally, thank you very much to my colleagues in GIFLE. We have laughed, we have cried (haven't we, Inés?), but most of all we have enjoyed ourselves. Thanks Silvia and Berta. "Our meetings in Switzerland" were always the best. Thanks to my University, the Universitat Politècnica de València for the FPI scholarship that allowed me to fulfill my dream. And of course, thanks to my Department, the DICGF, which for the last years has been my second home. III Agradecimientos Podríamos vivir en blanco y negro, pero afortunadamente la vida es en color. El color es fuente de emoción, de recuerdos, de sensaciones. Nos hace felices. Lo mismo sucede con las personas. Como los colores, hay personas que te calman, te evocan recuerdos, te abrazan, te sonríen. Mi agradecimiento va en primer lugar a estas personas, que como los colores, han dado plenitud a mi vida. Especialmente a mis padres, mi hermana y mis amigos, que siempre han estado ahí, y siguen haciéndolo. Durante el doctorado, han habido momentos de luz y oscuridad. Ha sido un camino largo y arduo, pero ha merecido la pena. He aprendido mucho. Gracias José Luis yÁngel por haberme guiado durante estos años. Vuestras contribuciones han sido esenciales para llenar de color esta tesis. Gracias también a un simple mail. Un mail que cambiaría mi vida. Gracias Stephen por responder afirmativamente a mi petición, y permitirme seis meses asombrosos en Leeds, UK, colaborando en el Colour Research Group de la School of Design. ¡Un sueño hecho realidad! Gracias también a Zeynep, por la estancia de un mes en Mimar Sinan Fine Arts University, Estambul, Turquía. He disfrutado de vistas y monumentos asombrosos. Cuando pienso en Estambul, pienso en colores. ¡Gracias a todos! Porúltimo, muchas gracias a mis compañeros en GIFLE. Hemos reído, hemos llorado (¿verdad Inés?), pero sobre todo hemos disfrutado. Gracias Silvia y Berta. 'Nuestras reuniones en Suiza' siempre fueron lo mejor. Gracias a mi universidad, la Universitat Politècnica de València por la beca FPI que me ha permitido cumplir mi sueño. Y por supuesto, gracias a mi Departamento, el DICGF, que durante losúltimos años ha sido mi segunda casa. V Summary Cultural heritage documentation and preservation is an arduous and delicate task but not trivial, in which color plays a fundamental role. Factors such as the di culty of reading the pigment, the complexity of the support and the variations in environmental lighting make color specification a di cult undertaking. However, the correct determination of color provides vital information on a descriptive, technical and quantitative level. Color allows a better understanding of the study area and o↵ers vital information not only on its current state but also on the aging of the pigments. Classical color documentation methods in archaeology were usually restricted to strictly subjective procedures, based on direct visual observations supported by color charts. However, this methodology has practical and technical limitations, a↵ecting the results obtained in the determination of color. Nowadays, it is frequent to support classical methods with geomatics techniques, such as photogrammetry or laser scanning, together with digital image processing and enhancement techniques. The use of these novel techniques has represented a notable advance. In fact, issues such as the precise geometric description of historical objects have been solved. However, there are still aspects to be addressed, such as the correct specification of color. Although digital images allow color to be captured quickly, easily, and in a non-invasive way, the RGB data provided by the camera does not itself have a rigorous colorimetric sense. Therefore, a rigorous transformation process to obtain reliable color data from digital images is required. This thesis proposes a novel technical solution, in which the integration of spectrophotometric and colorimetric analysis is intended as a complement to photogrammetric techniques that allow an improvement in color identification and representation of pigments with maximum reliability in 3D surveys, models and reconstructions. The proposed methodology is based on the colorimetric characterization of digital sensors, which is of novel application in cave paintings. The characterization aims to obtain the transformation equations between the device-dependent color data recorded by the camera and the independent, physically-based color spaces, such as those established by the Commission Internationale de l'Éclairage (CIE).

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, 2017

Abstract. Mapping surveys based on terrestrial laser scanning (TLS) are common nowadays for diffe... more Abstract. Mapping surveys based on terrestrial laser scanning (TLS) are common nowadays for different purposes such as documentation of cultural heritage assets. The chance to extract relevant information from TLS surveys depends not only on the fast acquisition of XYZ coordinates, but also on the meaningful intensity values of the fired objects. TLS behaviour depends on several known factors such as distance, texture, roughness, colour and albedo. This paper seeks to find out the mathematical relationship between the TLS intensity values and the colorimetric data using a colour chart. In order to do so, objective colour specification based on well-known colour spaces is needed. The approach used here started with scanning a colour chart containing a number of colour patches with known chromatic and reflection characteristics. After several transformations, the results allowed us to characterise the intensity behaviour of a time-of-flight laser scanner. The characterisation of the i...

Rock art documentation is a complex task that should be carried out in a complete, rigorous and e... more Rock art documentation is a complex task that should be carried out in a complete, rigorous and exhaustive way, in order to take particular actions that allow stakeholders to preserve the archaeological sites under constant deterioration. The pigments used in prehistoric paintings present high light sensitivity and rigorous scientific color degradation mapping is not usually undertaken in overall archaeological sites. Microfading spectrometry is a suitable technique for determining the light-stability of pigments found in rock art paintings in a non-destructive way. Spectral data can be transformed into colorimetric information following the recommendations published by the Commission Internationale de l’Eclairage (CIE). The fading degree can be evaluated through the color changes produced, computing both color and chromatic differences. Microfading Tester (MFT) measurements on spot samples are time-consuming and difficult to materialize on-site. This paper presents the results of s...

Remote Sensing

The camera characterization procedure has been recognized as a convenient methodology to correct ... more The camera characterization procedure has been recognized as a convenient methodology to correct color recordings in cultural heritage documentation and preservation tasks. Instead of using a whole color checker as a training sample set, in this paper, we introduce a novel framework named the Patch Adaptive Selection with K-Means (P-ASK) to extract a subset of dominant colors from a digital image and automatically identify their corresponding chips in the color chart used as characterizing colorimetric reference. We tested the methodology on a set of rock art painting images captured with a number of digital cameras. The characterization approach based on the P-ASK framework allows the reduction of the training sample size and a better color adjustment to the chromatic range of the input scene. In addition, the computing time required for model training is less than in the regular approach with all color chips, and obtained average color differences Δ E a b * lower than two CIELAB u...

Proceedings - 1st Congress in Geomatics Engineering - CIGeo, Jul 5, 2017

Archaeological documentation is a complex process where the technical measurement and specificati... more Archaeological documentation is a complex process where the technical measurement and specification of colour is a key aspect. In the last years heritage documentation processes have largely benefited from the application of digital recording methods, imagery analysis software and technologies that offers great advantages over the traditional methods. The rigorous processing of colourimetric data requires software packages with specific colourimetric technical characteristics. In this paper we report on our in-house pyColourimetry software that was developed and tested taking into account the recommendations of the Commission Internationale de l'Éclairage (CIE). The objective is to apply a rigorous procedure for the characterisation of cameras based a priori on polynomial models. Most of the digital cameras capture colour information in the well-known RGB format, but the signals generated by the digital camera are device dependent. By means of the characterisation we establish the relationship between device dependent RGB values and the tristimulus coordinates defined by the CIE standard colourimetric observer. Once the camera is characterised, users have the potential to obtain output images in the sRGB space that is independent of the sensor of the camera. pyColourimetry software allows users to control the entire digital image processing and the colourimetric data workflow proposed. We applied the methodology on a set of pictures targeting Levantine rock art motifs in Cova dels Cavalls (Castellón, Spain) which is considered part of a UNESCO World Heritage Site. The outcomes obtained are satisfactory and very promising for proper colour documentation in cultural heritage estudies.

Sensors

In this paper, we propose a novel approach to undertake the colorimetric camera characterization ... more In this paper, we propose a novel approach to undertake the colorimetric camera characterization procedure based on a Gaussian process (GP). GPs are powerful and flexible nonparametric models for multivariate nonlinear functions. To validate the GP model, we compare the results achieved with a second-order polynomial model, which is the most widely used regression model for characterization purposes. We applied the methodology on a set of raw images of rock art scenes collected with two different Single Lens Reflex (SLR) cameras. A leave-one-out cross-validation (LOOCV) procedure was used to assess the predictive performance of the models in terms of CIE XYZ residuals and Δ E a b * color differences. Values of less than 3 CIELAB units were achieved for Δ E a b * . The output sRGB characterized images show that both regression models are suitable for practical applications in cultural heritage documentation. However, the results show that colorimetric characterization based on the Ga...

ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences

Proceedings

Image-based characterisation offers accurate results for colour recording in cultural heritage do... more Image-based characterisation offers accurate results for colour recording in cultural heritage documentation tasks. Although numerous researches are focused on improving either the mathematical model used or the workflow technical details, in this paper we propose the use of selected skin-tone colours instead of the full colour checker dataset. Even though the two datasets yield good colourimetric results, an improvement is observed when using the skin-tone samples. The results reveal two key aspects in the characterisation procedure, specifically the number of samples and the use of training data near the chromatic range of the scene used in the characterisation procedure itself.

Color Research & Application

Determining the correct colour is essential for proper cultural heritage documentation and catalo... more Determining the correct colour is essential for proper cultural heritage documentation and cataloguing. However, the methodology used in most cases limits the results since it is based either on perceptual procedures or on the application of colour profiles in digital processing software. The objective of this study is to establish a rigorous procedure, from the colourimetric point of view, for the characterisation of cameras, following different polynomial models. Once the camera is characterised, users obtain output images in the sRGB space that is independent of the sensor of the camera. In this paper we report on pyColourimetry software that was developed and tested taking into account the recommendations of the Commission Internationale de l'Éclairage (CIE). This software allows users to control the entire digital image processing and the colourimetric data workflow, including the rigorous processing of raw data. We applied the methodology on a picture targeting Levantine rock art motifs in Remigia Cave (Spain) that is considered part of a UNESCO World Heritage Site. Three polynomial models were tested for the transformation between colour spaces. The outcomes obtained were satisfactory and promising, especially with RAW files. The best results were obtained with a second order polynomial model, achieving residuals below three CIELAB units. We highlight several factors that must be taken into account, such as the geometry of the shot and the light conditions, which are determining factors for the correct characterisation of a digital camera.

Articles by Adolfo Molada Tebar

Color data are often required for cultural heritage documentation. These data are typically acqui... more Color data are often required for cultural heritage documentation. These data are typically acquired via standard digital cameras since they facilitate a quick and cost-effective way to extract RGB values from photos. However, cameras’ absolute sensor responses are device-dependent and thus not colorimetric. One way to still achieve relatively accurate color data is via camera characterization, a procedure which computes a bespoke RGB-to-XYZ matrix to transform camera-dependent RGB values into the device-independent CIE XYZ color space. This article applies and assesses camera characterization techniques in heritage documentation, particularly graffiti photographed in the academic project INDIGO. To this end, this paper presents COOLPI (COlor Operations Library for Processing Images), a novel Python-based toolbox for colorimetric and spectral work, including white-point-preserving camera characterization from photos captured under diverse, real-world lighting conditions. The results highlight the colorimetric accuracy achievable through COOLPI’s color-processing pipelines, affirming their suitability for heritage documentation.