This paper presents a new design, calibration procedures, and an optimized capturing strategy, of a 3D imaging system for capturing very large paintings. It describes relevant design requirements and constraints, various (improved) calibration steps, and additional capturing automation, aimed at optimally and efficiently capturing the characteristic topographical features, such as impasto and craquelure, of (17th century, Dutch) paintings. The 3D imaging system was used to capture Rembrandt van Rijn's 'The Night Watch' (1642), a painting with a surface area of more than 17m2. We highlight some preliminary result of this scanning campaign and possible applications such as painting documentation, condition analysis, and visualization. ... Read more

Fast, accurate and low-cost 3D scans are the key in designing personalized products. In this paper, using close-range photogrammetry technique, we aim at finding the “just enough” number of cameras and their spatial configurations for a full 3D reconstruction of the human hand. Given an object, we establish a mathematical model to describe the 3D constructible ratio based on the field of the view and the depth of field of each camera, as well as the visibility of each part of the object in the view of each camera. Furthermore, we introduce spatial constrains to arrange cameras along two rings for: 1) solving the problem of the large number of parameters in the unconstrained optimization, and 2) the feasibility and flexibility in the construction. Based on the found number of cameras and the spatial configuration of each camera, a prototype scanner was built to verify the effectiveness of the proposed method. The mean absolute error between the 3D scan of a 3D printed hand and its original CAD model was found to be 0.38mm, which is smaller than that (0.52mm) of using the conventional setup. Besides, the distribution of errors is smaller as well, which implicates a better full 3D reconstruction of the scanned hand. ... Read more

High fidelity reproductions of paintings provide new opportunities to museums in preserving and providing access to cultural heritage. This paper presents an integrated system which is able to capture and fabricate color, topography and gloss of a painting, of which gloss capturing forms the most important contribution. A 3D imaging system, utilizing stereo imaging combined with fringe projection, is extended to capture spatially-varying gloss, based on the effect of specular reflectance polarization. The gloss is measured by sampling the specular reflection around Brewster’s angle, where these reflections are effectively polarized, and can be separated from the unpolarized, diffuse reflectance. Off-center gloss measurements are calibrated relative to the center measurement. Off-specular gloss measurements, following from local variation of the surface
normal, are masked based on the height map and corrected. Shadowed regions, caused by the 3D relief, are treated similarly. The area of a single capture is approximately 180x90mm at a resolution of 25x25μm. Aligned color, height, and gloss tiles are stitched together off-line, registering overlapping color regions. The resulting color, height and gloss maps are inputs for the poly-jet 3D printer. Two paintings were reproduced to verify the effectiveness and efficiency of the proposed system. One painting was scanned four times, consecutively rotated by 90 degrees, to evaluate the influence of the scanning system geometric configuration on the gloss measurement. Experimental results show that the method is sufficiently fast for practical application, i.e. to scan a whole painting within eight hours, during closing hours of a museum. The results can well be
used for the purpose of physical reproduction and other applications needing first-order estimates of the appearance (e.g. conservation diagnostics and condition reports). Our method to extend appearance scanning with gloss measurements is a valuable addition in the quest for realistic reproductions, in terms of its practical applicability - number of images needed for reconstruction and speed - and its perceptual added value, when added to color and topography reproduction. ... Read more

Being able to link captured material characteristics and fabricable material appearance attributes is important for creating
life-like reproductions. In this paper we propose a method for gloss calibration, and an approach for gloss gamut mapping, as
part of an integrated approach for color, topography and gloss reproduction. For gloss calibration, gloss calibration targets
were printed in the primary printing colors (CMYK and White), with uniform gloss in equal distant gloss levels. These targets
were scanned using the proposed gloss scanner. To create the gloss gamut map, a monotonic curve was fitted to the mean gloss
scan values at different gloss levels. Analysis of fitted curves indicated that the gloss mapping is independent of the diffuse
colors. As a case study, the painting ‘Fruit Still Life’ by Cornelis de Heem was scanned, and the measured gloss was mapped
to printable gloss levels using the relation described by the fitted curve. The printed result shows good correspondence to the
painting’s appearance, with clearly distinguishable gloss features for the in-gamut glass values. ... Read more

The aging of paintings is inevitable and over the years degradation occurs due to exposure to a variety of environmental influences. One of these degradations is craquelure, fracture patterns in the paint. 3D imaging techniques offer opportunities to capture the surface of a painting and these patterns at high resolution. In this paper we present a 3D scanner that is able to capture surface topography and color of oil paintings at high resolution utilizing fringe-encoded stereo imaging scanning system. The scanner is capable of automated capture of an area of 1x1m2, capturing a painting at a spatial resolution of 7 micron and a depth accuracy of 34 microns. Scanning at this resolution creates potential research opportunities for documentation and monitoring oil paintings under its environmental influences. A scan was made of 'Girl with a Pearl Earring' (c.1665), painted by Johannes Vermeer, which exhibits fine craquelure patterns. The scanner is able to capture the painting of 39x44.5 cm within 2 hours with a tile overlap of 25%. The results showed that the craquelure has more often a ridge-shaped profile instead of the expected inward valleys. The documentation of these variations in crack profiles create interesting paths for future research. ... Read more

High fidelity reproductions of paintings provide new opportunities to museums in preserving and providing access to cultural heritage. This paper presents an integrated system which is able to capture and fabricate color, relief and gloss of a painting's surface, emphasizing on gloss capturing. To measure the spatially varying gloss, the specular reflection of the center of the scanned area is sampled at the Brewster angle, utilizing the effect of reflectance polarization at this angle. The off-center gloss measurements are corrected using the perpendicular and parallel reflectance coefficients, relative to the center measurement. Shadows in the gloss map, which are caused by 3D relief of the surface, are masked based on the height map and then filled by interpolating surrounding gloss information. The captured color image, height map and gloss map are inputs for the 3D printer. A painting "Two wrestling figures in the style of Van Gogh" was reproduced to verify the effectiveness and efficiency of the proposed system. Experiment results indicate that the proposed system gives accurate enough gloss measurement of the painting's surface for the purpose of gloss fabrication. ... Read more