Photographer-Friendly Work-Flows for Image-Based Modelling of Heritage Artefacts

Abstract

ABSTRACT:Because of its low-cost and ease in use, 3D reconstruction from sets of images has an great potential for enhancing cultural heritage documentation, conservation and valuation. However, these technologies, from image acquisition to final 3D model obtaining, are often difficult to master for non-expert people. Our work consists in developing a series of acquisition protocols for the museum's photographs. The end-goal being to enable those professionals to generate efficiently and easily 3D models of heritage artefact. 1.INTRODUCTIONSince the recent convergence of the researches in the fields of photogrammetry and computer vision, photogrammetric results relevant for the documentation and the study of heritage artefacts (archaeological fragments, paintings, sculptures, furnitures, architectural elements, buildings, sites) can be computed with high quality photographs without others data, through the APERO and MICMAC pipeline for example (Pierrot-Deseilligny, 2011).How to precisely define this quality? There is both a photographic quality (definition of the picture, sharpness, dynamic range, etc.) and the correct setting of parameters linked with the image-based modelling constraints, especially the spatial configuration of the points of view.Nonetheless the settling of these parameters cannot be the same for all cases since the artefacts have very different characteristics. Thus the whole corpus must be divided within a technical typology including morphology, scale, brightness, etc.. Each group of these classifications lead the photographers to a suitable protocol. It explains how to choose the different points of view, how to enlighten the artefact, etc.. The photographs taken are then processed with the web interface on cloud. The whole pipeline, including photogrammetric acquisition, data processing, data indexing and data exploitation is the aim of the Culture 3D Clouds: synthesize technical solutions for 3D surveying. New businesses and technical models can emerge in the institutions that houses and cares for collections of artefacts. The photographer working in these institutions could learn and develop a practice of photogrammetry. CONSTRAINTSThe combined computer vision/photogrammetry approach of APERO for estimation of initial solution allows a certain flexibility in the data acquisition, for example a leeway in choosing the points of view. The photographers can even shoot without a tripod if the shutting time allows it.The automatic process consists in tie-points extraction (with SIFT algorithm), internal and external orientation by bundle adjustment (Apero), and dense image matching (Micmac). The final output is a set dense and accurate pointclouds.However in order to make the relative orientation converge and to produce precise results, some constraints have to be respected:• for each desired points cloud take a "master" image and several closed associated images (with low ratio base to distance and important overlapping) (Pierrot-Deseilligny, 2011), • between each master image take a suffici...

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