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Figure 1 shows one scan of the middle toe of David's right foot, taken from our full-resolution dataset. The X-Y resolution of our scanner is 0.29mm (290 microns), and its Z-resolution is 0.05mm (50 microns). Figure 2 shows a corresponding scan acquired by the National Research Council of Canada's ultra-high-resolution laser triangulation scanner. The X-Y resolution of their scanner is 0.05mm (50 microns), and its Z-resolution is 0.01mm (10 microns). Figure 3 is a photograph for comparison. Figure 4 shows a closeup of the central portion of the toenail, and figure 5 is a plot of depth as a function of position along the red line in figure 4. The grid in figure 5 is marked in 10th's of a millimeter and is distorted vertically to improve readability.
Our reason we asked the NRC to make these scans was to give us a gold standard for our own data. Another reason was to help us understand the noise we were seeing in our data. As figure 2 shows, although their resolution is better than ours, their scans also exhibited unexpected noise. In the images above, the few large pits in the toenail, which measure about 0.5mm across, are real, but the fine-grain roughness, which measures 50-150 microns peak-to-peak in our scan and 10-30 microns in theirs, is not. Polished marble is smoother than this. Our hypothesis is that this noise arises from scattering of the laser within the crystal structure of the marble, not from noise in our camera or scanning systems. This suggests that we have reached the limit of laser scanning technology, at least for marble.
Much as we might like to digitize Michelangelo's statues at the extraordinary resolution shown in figure 2, it is currently impractical. Aside from the large size of their scanner, which is mounted on an optical bench, and the difficulty of holding such a scanner steady at a height of 24 feet, the datasets would simply be too large. Digitizing the David at at this resolution would produce 50 billion polygons and, with equivalent-resolution color data, would occupy over a terabyte.
Click here to read a technical paper giving some preliminary results of our study of the effect of subsurface scattering on laser scanning of marble surfaces.
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When people think of Michelangelo's David, they often think of his slim figure and tight abs (figure 1). Actually, his belly bulges considerably, as figure 2 shows. This bulge is missing from most handmade replicas of the statue, making them look too muscular and "tucked in." To be precise, the width of David's waist is 75 cm left to right at a in this annotated front view, and 53 and 57 cm front to back at b and c, respectively in this annotated side view. (The height of the David is approximately 497 cm from head to toe (i.e. without the carved rock on which he is standing.)
These renderings were made from a simplified polygon mesh model computed by Paolo Cignoni (CNR/Pisa) from the artificially colored 1.0 mm model of the statue from our archive.
In a letter to the editor of the New England Journal of Medicine, oncologist James Stark and art historian Jonathan Nelson have hypothesized that several visually obvious lumps and depressions on the left breast of Michelangelo's famous statue of Night represent an advanced stage of female breast cancer. Since we have digitized this statue, they asked for our help visualizing these lumps and measuring them. The image above shows a rendering of a low-resolution computer model of the breast. The view is looking down from above, i.e. from the viewpoint of Night's head. Two depressions are indeed visible, to the left and right of the nipple.
With the help of Marc Levoy, Stanford freshman May Allen took some measurements from this computer model wrote them up as a project for Marc's freshman seminar course CS 99D - The Science of Art. Here is her online report. Click here to read Nelson and Stark's letter.
Notice: The images of Michelangelo's statues that appear on this web page are the property of the Digital Michelangelo Project and the Soprintendenza ai beni artistici e storici per le province di Firenze, Pistoia, e Prato. They may not be copied, downloaded and stored, forwarded, or reproduced in any form, including electronic forms such as email or the web, by any persons, regardless of purpose, without express written permission from the project director Marc Levoy. Any commerical use also requires written permission from the Soprintendenza.
Notizia: Questi modelli elaborati al computer, immagini computerizzate, e fotografiche sono proprietà del Progetto Digitale Michelangelo e la Soprintendenza Per I Beni Artistici e Storici per le Province di Firenze, Pistoia e Prato. Non possono essere copiati, scaricati da internet su un file, inviati, o riprodotti in nessuna forma, incluso la posta elettronica o il web, da nessuna persona per nessun motivo, senza un permesso scritto da Marc Levoy, il direttore del progetto. Eventuali usi commerciali esigono anche il permesso scritto dalla Soprintendenza.
