A three-dimensional (3D) printer is one of the mechanical tools controlled by computers and is commonly used in "digital fabrication." The 3D printers have recently attracted much attention because of the State of the Union Address by US President Obama, the Maker Movement, and the market entry of affordable 3D printers. In contrast to the boom, however, accurate information on the actual capability of 3D printers is lacking and remains ill-defined. In this paper, the capabilities and application potential of 3D printers are presented from the perspective of a service bureau. The main discussions are focused on the following: (1) 3D printer is a digital mechanical tool that manufactures prototypes whose shapes are complex and are not suitable for removal processing, (2) it is not suitable for mass production from the viewpoints of cost, mechanical strength, and safety, and (3) it can manufacture only one high-value-added product by combining other techniques such as painting, casting, and so on.

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Three-dimensional (3D) printers have become popular in recent years as a means of generating geometries designed on CAD or 3D graphic systems. The price of 3D printers has been decreasing, and some are now even within the reach of ordinary consumers. The importance of the software for designing 3D objects will then increase when 3D printers become commonplace household items. In this article, we present an overview of the recent trend in 3D printing and introduce the geometry processing technologies studied in CAD and CG communities. Because the surface of an object that is to be printed has to be closed without any tiny holes, several techniques to generate watertight solid models from standard 3D data have been studied. Further, adding physical functions by modifying the object geometry is one of the recent research trends. We introduce recent studies and show two of our research projects on designing 3D objects for 3D printing: one is the design of ornaments with geometrical symmetry, which is the same as that of regular polyhedra, and the other is the design of a geometrical toy named sphericon. Both design systems employ voxel-like data structure to ensure that the surface is closed. Finally, we conclude our studies by discussing the potential of 3D printing technology.

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Import of dangerous devices such as weapons is restricted by customs, but a novel problem arises where we can download a set of 3D-CAD data for weapons from foreign websites and indirectly obtain physical weapons using a 3D-printer. In the future, as the precision of 3D scanners will improve, creation of copyright-violating objects will proliferate not only for private use but also for commercial use by producing metallic molds. We are considering the development of three types of security techniques with regard to 3D-printer applications: a 3D polygon content security before printing, a fabrication process security for 3D printing, and traceability of fabricated objects after 3D printing. In this article, we focus on the second fabrication process, i.e., security for 3D printing. We propose a polygon-matching technique of the 3D-model data for a 3D-printer output by registering the models in a blacklist database to prevent the fabrication of dangerous devices or copyright-violating objects. For the polygon matching, we propose a polygon-reduction technique for rapid and efficient matching, which is similar to a triangle-seeking technique, and a normalizing technique of aligning the scale or angle of a given 3D-model to a predefined direction for precise matching. Then, we consider robust matching for decorated models or multiple-part constructed complex models. In this article, we present an overview of our proposed polygon-matching algorithms.

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The author introduces two types of new autostereoscopic displays where multiple viewers can enjoy 3D images without wearing special goggles. A coarse integral volumetric imaging display combines multiview and volumetric display technologies to realize simultaneous reduction in the vergence-accommodation conflict and expression of occlusion and specular lights. Using this display technology, multiple viewers can together enjoy viewpoint-specific stereo images. However, this display resolution is not high enough because images must be simultaneously provided to the many viewpoints. Full-HD autostereoscopy can be realized by time-division multiplexing using a directional backlight composed of a convex lens array and dot-matrix light sources. To realize a directional backlight with uniform brightness using a coarse convex lens array, a special phase shift structure is introduced to align the lens array. This structure is combined with a vertical diffuser to mix the bright and dark parts of the elemental lenses without losing directionality of the light along the horizontal direction, which is needed to preserve autostereoscopy.

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In this article, basics and examples of Non-Photorealistic Rendering (NPR) are introduced. NPR is one of the categories of computer graphics (CG). In contrast with the traditional photorealistic approach in CG, NPR is to create images with artificial enhancement like illustration or painting. There are three major objectives in NPR: simulation of traditional drawing techniques, visual information communication, and support for existing drawing techniques. As for implementations, NPR techniques can be classified from several points of view, such as a degree of user interaction, input data (2D image or 3D scene data), etc. From 2D images, NPR images can be created by several approaches such as stroke-based drawing, image decomposition, and image analogies. From 3D scene data, NPR techniques can be added on or replaced by traditional photorealistic rendering. Especially, it is effective to use line drawing techniques such as contour ⁄ edge drawing and hatching. For moving images, it is important to keep continuity between frames, especially for strokes. Shape deformation is also an important issue in NPR. In addition to shape exaggeration, multi viewpoint projection is used for deformation.

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