Deducing Ink-Transmittance Spectra from Reflectance and Transmittance Measurements of Prints

The color of prints is mainly determined by the light absorption of the inks deposited on top of paper. In order to predict the reflectance spectrum of prints, we use a spectral prediction model in which each ink is characterized by its spectral transmittance. In the present paper, we consider two classical reflectance prediction models: the Clapper-Yule model and the Williams-Clapper model. They rely on a same description of multiple reflection-transmission of light, but use a different description of the attenuation of light by the inks. In the Clapper-Yule model (non-orientational ink attenuation), the orientation of light traversing the ink is not taken into account. In the Williams-Clapper model, it is taken into account (orientational ink attenuation). In order to determine experimentally which of these two models is the more suitable for a given type of print, we propose a method using the reflectance and the transmittance of prints. We introduce a bimodal model, enabling spectral reflectance and transmittance predictions. Depending whether the direction of light into the ink is taken into account, we obtain a non-orientational bimodal model or an orientational bimodal model. Using these two models, we deduce the ink transmittance spectrum from various reflectance and transmittance measurements performed on a same print, and compare the different deduced spectra. The model which is the most adapted to the considered print is the one where the deduced spectra best match each other

Compositional reflectance and transmittance model for multilayer specimens

We propose a compositional model for predicting the reflectance and the transmittance of multilayer specimens composed of layers having possibly distinct refractive indices. The model relies on the laws of geometrical optics and on a description of the multiple reflection-transmission of light between the different layers and interfaces. The highly complex multiple reflection-transmission process occurring between several superposed layers is described by Markov chains. An optical element such as a layer or an interface forms a biface. The multiple reflection-transmission process is developed for a superposition of two bifaces. We obtain general composition formulas for the reflectance and the transmittance of a pair of layers and/or interfaces. Thanks to these compositional expressions, we can calculate the reflectance and the transmittance of three or more superposed bifaces. The model is applicable to regular compositions of bifaces, i.e., multifaces having on each face an angular light distribution that remains constant along successive reflection and transmission events. Kubelka's layering model, Saunderson's correction of the Kubelka-Munk model, and the Williams-Clapper model of a color layer superposed on a diffusing substrate are special cases of the proposed compositional model

A Parallel PC-based Visible Human Slice WEB server

Visualization of 3D tomographic images by slicing, i.e. by intersecting a 3D tomographic image with a plane having any desired position and orientation is a tool of choice both for learning and for diagnosis purposes. In this project, a parallel Visible Human Slice Web server has been developed, which offers to any Web client the capability of interactively specifying the exact position and orientation of a desired slice and of requesting and obtaining that slice from a 3D tomographic volume, made of either CT, MRI or cryosection images (digital color photographs of cross-sections). For interactive slice position and orientation, a miniature 3D version of the full image is used

Authentication of documents and valuable particles by using moire intensity profiles

This invention discloses new methods, security devices and apparatuses for authenticating documents and valuable articles which may be applied to any support, including transparent synthetic materials and traditional opaque materials such as paper. The invention relates to moire intensity profiles which occur in the superposition of periodic or aperiodic geometrically transformed structures. By using a specially designed basic screen and master screen, where at least the basic screen is comprised in the document, a moire intensity profile of a chosen shape becomes visible in their superposition, thereby allowing the authentication of the document. If a microlens structure is used as a master screen, the document comprising the basic screen may be printed on an opaque reflective support, thereby enabling the visualization of the moire intensity profile by reflection. Automatic document authentication is supported by an apparatus comprising a master screen, an image acquisition means such as a camera and a comparing processor whose task is to compare the acquired moire intensity profile with a reference image. Depending on the match, the document handling device connected to the comparing processor accepts or rejects the document. An important advantage of the present invention is that it can be incorporated into the standard document printing process, so that it offers high security at the same cost as standard state of the art document production