Abstract: We disclose a method for printing by rotogravure, flexography, offset, inkjet or electrophotography invisible images that are viewable under UV light. The method generates juxtaposed dispersed dot halftones by first creating juxtaposed clustered dot halftones and by applying to them dispersed dot halftoning according to a blackness reduction factor. Dispersed dot halftoning is embodied by random threshold error diffusion. The resulting dispersed dot halftones comprise pixel segments located within the areas defined by the clustered dots. These pixel segments specify the areas of the cells to be engraved onto the rotogravure cylinder. For offset, they can be imaged onto an offset plate or for electrophotography, onto a photoconductor. The disclosed juxtaposed dispersed dot halftoning method can be embedded into a framework for the reproduction of fluorescent full color images with three or more invisible fluorescent inks. These invisible fluorescent color images offer a strong protection against counterfeits.

Abstract: Methods are disclosed for hiding a two-dimensional code such as a QR code within a visible layer of randomly scattered line segments. The scattering parameters comprise the length of successive line segments as well as their relative offsets. These parameters are stored in a key. The hidden 2d code is recovered with a computing device such as a smartphone carrying out the acquisition, perspective correction, and rectification of the visible layer of scattered line segments. This computing device synthesizes in its memory according to that same key a hidden layer of scattered line segments. The superposition of the acquired, perspectively corrected and rectified visible layer and of the hidden layer yields an image from which the hidden 2D code is revealed. The presented methods enable the secret transmission of information from the real world of documents and objects to databases located on computer networks.

Abstract: Moiré is an appealing visual effect observable when two or more repetitive patterns are superposed. We introduce a method for designing and fabricating level-line moirés on curved surfaces. These moiré shapes are obtained by superposing a partly absorbing or partly light deviating curved base layer and a curved revealing layer formed by a grating of transparent lines or cylindrical lenses. The distances between base layer and revealing layer are adapted to the locally varying distances between successive transparent lines or cylindrical lenses of the curved revealing layer grating. We demonstrate the quality of our method by rendered simulations and by fabrication. The resulting level-line moiré display devices can be manufactured using different fabrication techniques, from multi-material 3D printing to molding.

Abstract: The present disclosure describes a method and computerized means for creating dynamically evolving moiré shapes on curved surfaces. The method applies geometrical transformations in order to obtain curvilinear moirés and creates the moirés on curved surfaces by applying mappings from planar space to 3D space. The method relies on the superposition of a base layer with base bands and of a revealing layer with sampling elements. The dimensions of the revealing layer sampling elements such as cylindrical or spherical lenses as well as the distances between the base and revealing layer surfaces are adapted to the space between neighbouring isoparametric lines that define the curved surface. The resulting moiré shapes evolve smoothly on the specified curved surface and show recognizable shapes such as words, letters, numbers, flags, logos, graphic motifs, drawings, clip art, and faces.

Abstract: The present disclosure describes an authentication and tracking system relying on spatial codes hidden into a grayscale, variable intensity or color multigrating reproduced on a substrate. The authentication software running in a smartphone takes pictures of the multigrating and applies perspective correction and fine grain rectification. The hidden spatial code is made apparent by the phase-controlled superposition of the fine grain rectified multigrating and a corresponding digital revealing layer grating. Subsequent image processing operations enable extracting the hidden spatial code, decode it and authenticate the corresponding document or good, by sending the decoded message to an authentication and tracking computing server. Applications include the authentication and tracking of documents and goods as well as the localization of persons.