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Virtual whitening of fossils using polynomial texture mapping

Øyvind Hammer and Jelena Spocova

Plain Language Abstract

Paleontologists traditionally coat their fossils with white powder prior to photography. This "whitening" removes uninformative colour variation, enhancing the 3D information in the image. Whitening can produce stunning images, but is a somewhat cumbersome procedure. We show that by taking many pictures of an uncoated fossil, each with a different light source, the colour variation can be mathematically separated from the shading due to the 3D shape. The fossil can then be whitened virtually in the computer.

Resumen en Español

Blanqueamiento virtual de fósiles mediante el use de mapeo de textura polinomial

El Mapeo de Textura Polinomial (PTM) es una conocida técnica de la fotografía digital que permite la reiluminación y modificación virtual de las propiedades de la superficie reflectante con objeto de resaltar detalles escasamente perceptibles. En este artículo describimos un nuevo y sencillo método para transformar archivos PTM que imiten el blanqueamiento, un procedimiento habitual en la fotografía de fósiles. El método se basa en la estimación de los vectores normales de superficie a partir de los coeficientes PTM. Estos vectores se utilizan para construir un modelo de iluminación difusa e isotrópica (modelo de Lambert) que depende exclusivamente de la inclinación de la superficie. Resulta posible también incrementar el efecto del agente blanqueador no penetrando en las depresiones, con lo que aumenta el contraste debido al relieve.

Palabras clave: mejora de la imagen; tratamiento de imágenes digitales; ilustración; PTM

Traducción: Miguel Company

Résumé en Français

Blanchiment virtuel de fossiles utilisant le Mappage de Texture Polynomial

Le Mappage de Texture Polynomial (PTM) est une technique courante en photographie digitale, permettant un re-éclairage virtuel et des modifications des propriétés de la surface réflective afin de faire apparaitre des détails subtiles. Nous décrivons une nouvelle méthode simple pour transformer les fichiers PTM afin de reproduire le blanchiment, une procédure traditionnelle pour la photographie des fossiles. La méthode repose sur une estimation des vecteurs normaux de la surface à partir de coefficients du PTM. Ces vecteurs sont utilisés pour construire un model de lumière isotropique (Lambertien) diffuse qui dépend uniquement de l'inclinaison de la surface. Il est également possible de simuler l'effet d'un agent de blanchiment ne pénétrant pas dans les dépressions, augmentant le contraste lié à la topographie.

Mots clés: amélioration de l'image; illustration digitale; illustration; PTM

Translator: Olivier Maridet

Deutsche Zusammenfassung

Virtuelles Aufhellen von Fossilien mit polynomem Textur-Mapping

Polynomes Textur-Mapping (PTM) ist eine in der Digitalfotografie etablierte Technik. Sie ermöglicht die virtuelle Aufhellung und die Bearbeitung von Oberflächenreflexionen, um kleinste Details herauszuarbeiten. Wir beschreiben eine neue, einfache Methode, um PTM-Dateien umzuwandeln. Sie imitiert Aufhellung, eine traditionelle Vorgehensweise beim Fotografieren von Fossilien. Die Methode beruht auf einer Abschätzung von Flächennormalen-Vektoren aus den PTM-Koeffizienten. Diese Vektoren werden benutzt, um ein diffuses, isotropisches (Lambertinisches) Beleuchtungsmodell zu erstellen, das nur von lokalen Höhenvariationen abhängt. Es ist ebenso möglich den Weissmachereffekt zu simulieren, der nicht in Vertiefungen eindringt und damit den Topographie-abhängigen Kontrast erhöht.

Schlüsselwörter: Bildverbesserung; digitale Bildgebung; Illustration; PTM

Translator: Eva Gebauer

Arabic

384 arab

Translator: Ashraf M.T. Elewa

 

 

Øyvind Hammer, This email address is being protected from spambots. You need JavaScript enabled to view it.
oyvindNatural History Museum
University of Oslo
Pb. 1172 Blindern
0318 Oslo
Norway

Øyvind Hammer is a paleontologist at the Natural History Museum in Oslo. He mainly works in the Lower Palaeozoic, Jurassic and Quaternary of Norway, including the Arctic and offshore areas.
PE Note: artwork from an earlier Hammer paper was the cover for the first issue of PE.

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Jelena Spocova, This email address is being protected from spambots. You need JavaScript enabled to view it.
jelenaNorwegian Broadcasting Corporation
Pb. 8500 Majorstuen
0340 Oslo
Norway

Jelena Spocova is a software engineer, currently working as developer in the Norwegian Broadcasting Corporation.

 

FIGURE 1. 1: Upper Jurassic shell bed, Svalbard, with ammonite (Dorsoplanites sp.) and bivalves (mainly Buchia sp.). PMO 217.501. Field of view 14 cm. Virtually relighted PTM image, comparable with an unprocessed standard photograph. 2: Physically painted black, followed by ammonium chloride whitening, standard photography, some contrast stretch.

fig 1

FIGURE 2. Best effort virtual whitening with Phong shading using the specular enhancement method of Malzbender et al. (2000), with low exponent value to reduce shininess.

fig 2

FIGURE 3. For each pixel with position (u, v) in the image plane, luminosity is modelled with a biquadratic polynomial as a function of incoming light direction. The direction is given by the projection (lu, lv) of the light vector (normalized to unit length) onto the image plane.

fig 3

FIGURE 4. Virtual whitening of a trilobite (Bathyuriscus sp., Middle Cambrian, British Columbia), length 3 cm. 1: Virtually relighted grayscale PTM image, no further processing. 2: Virtually whitened. 3: Virtually whitened, with black paint effect. Note the darkening of concave features, e.g., on the pleural furrows.

fig 4

FIGURE 5. 1: Virtual whitening of an Upper Jurassic shell bed, cf. Figures 1-2. 2: Virtually whitened, with black paint effect.

fig 5

FIGURE 6. Virtual whitening of an Upper Jurassic mega-onychite (4 cm long), Svalbard. PMO 223.379. 1: Original image. 2: Virtually whitened, without black paint effect.

fig 6

FIGURE 7. Virtual whitening of a Middle Ordovician trilobite pygidium (Ogygiocaris, Oslo Region, PMO 60422). 1: Original image. 2: Virtually whitened, without black paint effect. The sharp colour transition in the original has been completely removed, and terrace lines are greatly enhanced.

fig 7