Abstract:The ability of High Dynamic Range (HDR) imaging to capture the full range of lighting in a scene has prompted an increase in its use for Cultural Heritage (CH) applications. Photogrammetric techniques allow the semi-automatic production of three-dimensional (3D) models from a sequence of images. Current photogrammetric methods are not always effective in reconstructing images under harsh lighting conditions, as significant geometric details may not have been captured accurately within under-and over-exposed regions of the image. HDR imaging offers the possibility to overcome this limitation, however the HDR images need to be tone-mapped before they can be used within existing photogrammetric algorithms. In this paper we evaluate four different HDR tone-mapping operators (TMOs) that have been used to convert raw HDR images into a format suitable for state-of-the-art algorithms, and in particular keypoint detection techniques. The evaluation criteria used are the number of keypoints, the number of valid matches achieved and the repeatability rate. The comparison considers two local and two global TMOs. HDR data from four CH sites were used: Kaisariani Monastery (Greece), Asinou Church (Cyprus), Château des Baux (France) and Buonconsiglio Castle (Italy).Key words: high dynamic range (HDR) imaging, HDR tone-mapping, keypoint detection, image-based 3D reconstruction Resumen:Las posibilidades que ofrecen las imágenes de alto rango dinámico (HDR) para registrar la totalidad del rango de iluminación de una escena han propiciado su creciente uso en aplicaciones de patrimonio cultural. Los métodos fotogramétricos actuales permiten la producción semi-automática de modelos tridimensionales (3D) a partir de una secuencia de imágenes. Sin embargo, éstos presentan serias limitaciones en escenas con iluminación dura, resultando en consecuencia la aparición de zonas expuestas o sobreexpuestas. En este tipo de condiciones, el uso de imágenes HDR ofrece la posibilidad de superar este problema. Para evaluar su potencialidad, se presentan en este artículo cuatro operadores diferentes de mapeado tonal (tone-mapping) en imágenes HDR, conocidos como TMOs, cuya misión es convertir las imágenes HDR crudas en un formato adecuado para su uso en algoritmos de vanguardia, y en particular en técnicas de detección de entidades. Los criterios de evaluación que se utilizan para analizar su potencialidad son: el número de entidades detectadas, el número de correspondencias válidas y su índice de repetibilidad. En la comparación se incluyen TMOs, dos locales y dos globales. Se utilizan datos HDR tomados en cuatro sitios patrimoniales: el monasterio de Kaisariani (Grecia), la iglesia de Asinou (Chipre), el castillo de los Baux (Francia) y el castillo de Buonconsiglio (Italia).Palabras clave: toma de imágenes de alto rango dinámico (HDR), mapeado tonal HDR, detección de entidades, reconstrucción 3D basada en imágenes
No abstract
ABSTRACT:Documenting the relevant aspects in digitisation processes such as photogrammetry in order to provide a robust provenance for their products continues to present a challenge. The creation of a product that can be re-used scientifically requires a framework for consistent, standardised documentation of the entire digitisation pipeline. This article provides an analysis of the problems inherent to such goals and presents a series of protocols to document the various steps of a photogrammetric workflow. We propose this pipeline, with descriptors to track all phases of digital product creation in order to assure data provenance and enable the validation of the operations from an analytic and production perspective. The approach aims to support adopters of the workflow to define procedures with a long term perspective. The conceptual schema we present is founded on an analysis of information and actor exchanges in the digitisation process. The metadata were defined through the synthesis of previous proposals in this area and were tested on a case study. We performed the digitisation of a set of cultural heritage artefacts from an Iron Age burial in Ilmendorf, Germany. The objects were captured and processed using different techniques, including a comparison of different imaging tools and algorithms. This augmented the complexity of the process allowing us to test the flexibility of the schema for documenting complex scenarios. Although we have only presented a photogrammetry digitisation scenario, we claim that our schema is easily applicable to a multitude of 3D documentation processes.
Emulating human behaviour is a very desirable characteristic for virtual agents. There is plenty of literature that focuses on a single specific aspect of human behaviour emulation, but it is quite rare to find a collection of implementations encompassing several aspects of the problem. In this work we present VIRTUAL-ME (VIRTUal Agent Library for Multiple Environment), a library that provides programmers with a complete set of classes that assembles various human characteristics and makes it possible to build smart agents. The assessment of the library capabilities to populate a generic virtual environment is also discussed through the analysis of different case studies.
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