In this paper, we propose Paxel, a generic framework for modeling the interaction between a projector and a high-frequency pattern surface. Using this framework, we present two different application setups (cf. Fig. 1a): a novel colorchanging effect, created with a single projected image and only when the projection surface is changed from a pattern surface to a uniform white surface. The observed effect relies on the spatially different reflectance properties of these two surfaces. Using this approach, one can alter color proprieties of the projected image such as hue or chroma. Furthermore, for a specific color range, defined by an full color-changing sub-gamut, one can embed two completely different images, within a single static projection, from which either one will be revealed depending on the surface. The second application allows the creation of color images using a single channel projector. For this application, we present a full color projection created using a 365 nm ultraviolet (UV) projector in combination with fluorescent pigments (cf. Fig. 1b), enabling new display possibilities, such as projection through participating media, e.g. fog, while hiding the scattering of the projection light outside of the visible spectrum. Both presented approaches create effects that might be striking to the observer, making this framework useful for art exhibitions, advertisements, entertainment and visual cryptography. Finally, in Sec. VI, we provide an in-depth analysis of the reproducible colors based on input parameters, used in the presented algorithm, such as: pattern layout, dot size of the pattern and the number of the clusters formed by k-means algorithm (IV-B).

This paper introduces a novel photometric compensation technique for inter-projector luminance and chrominance variations. Although it sounds as a classical technical issue, to the best of our knowledge there is no existing solution to alleviate the spatial non-uniformity among strongly heterogeneous projectors at perceptually acceptable quality. Primary goal of our method is increasing the perceived seamlessness of the projection system by automatically generating an improved and consistent visual quality. It builds upon the existing research of multi-projection systems, but instead of working with perceptually non-uniform color spaces such as CIEXYZ, the overall computation is carried out using the RLab [10, pp. 243-254] color appearance model which models the color processing in an adaptive, perceptual manner. Besides, we propose an adaptive color gamut acquisition, spatially varying gamut mapping, and optimization framework for edge blending. The paper describes the overall workflow and detailed algorithm of each component, followed by an evaluation validating the proposed method. The experimental results both qualitatively and quantitatively show the proposed method significant improved the visual quality of projected results of a multi-projection display with projectors with severely heterogeneous color processing.

We present a geometric calibration method to accurately register a galvanoscopic scanning laser projection system (GLP) based on 2D vector input data onto an arbitrarily complex 3D-shaped projection surface. This method allows for accurate merging of 3D vertex data displayed on the laser projector with geometrically calibrated standard rasterization-based video projectors that are registered to the same geometry. Because laser projectors send out a laser light beam via galvanoscopic mirrors, a standard pinhole model calibration procedure that is normally used for pixel raster displays projecting structured light patterns, such as Gray codes, cannot be carried out directly with sufficient accuracy as the rays do not converge into a single point. To overcome the complications of accurately registering the GLP while still enabling a treatment equivalent to a standard pinhole device, an adapted version is applied to enable straightforward content generation. Besides the geometrical calibration, we also present a photometric calibration to unify the color appearance of GLPs and standard video projectors maximizing the advantages of the large color gamut of the GLP and optimizing its color appearance to smoothly fade into the significantly smaller gamut of the video projector. The proposed algorithms were evaluated on a prototypical mixed video projector and GLP projection mapping setup.

We present a new approach for the reproduction of color images on a metallic substrate that look bright and colorful under specular reflection observation conditions and also look good under non-specular reflection observation conditions. We fit amounts of both the white ink and the classical cyan, magenta and yellow inks according to a formula optimizing the reproduction of colors simultaneously under specular and non-specular observation conditions. In addition, we can hide patterns such as text or graphical symbols in one viewing mode, specular or non-specular, and reveal them in the other viewing mode. We rely on the trade-off between amounts of white diffuse ink and amounts of cyan, magenta and yellow inks to control lightness in specular and in non-specular observation conditions. Further effects are grayscale images that alternate from a first image to a second independent image when tilting the print from specular to non-specular reflection observation conditions. Applications comprise art and entertainment, publicity, posters, as well as document security.

We propose a color reproduction framework for creating specularly reflecting color images printed on a metallic substrate that change hue or chroma upon in-plane rotation by 90°. This framework is based on the anisotropic dot gain of line halftones when viewed under specular reflection. The proposed framework relies on a spectral prediction model specially conceived for predicting the color of non-rotated and of 90° in-plane rotated cross-halftones formed of superpositions of horizontal and vertical cyan, magenta and yellow line halftones. Desired non-rotated and rotated image colors are mapped onto the sub-gamut allowing for the desired hue or chroma shift and then, using a 6D correspondence table, converted to optimal cross-halftone ink surface coverages. The proposed recolorization and decolorization framework is especially effective for creating surprising effects such as image parts whose hues change, or gray regions that become colorful. It can be adapted to commercial printers capable of printing with cyan, magenta and yellow inks on substrates formed by an ink attracting polymer lying on top of a metallic film layer. Applications may include art, advertisement, exhibitions and document security.