Color Halftones Research Articles

Spectral Neugebauer-based color halftone prediction model accounting for paper fluorescence.

We present a spectral model for predicting the fluorescent emission and the total reflectance of color halftones printed on optically brightened paper. By relying on extended Neugebauer models, the proposed model accounts for the attenuation by the ink halftones of both the incident exciting light in the UV wavelength range and the emerging fluorescent emission in the visible wavelength range. The total reflectance is predicted by adding the predicted fluorescent emission relative to the incident light and the pure reflectance predicted with an ink-spreading enhanced Yule-Nielsen modified Neugebauer reflectance prediction model. The predicted fluorescent emission spectrum as a function of the amounts of cyan, magenta, and yellow inks is very accurate. It can be useful to paper and ink manufacturers who would like to study in detail the contribution of the fluorescent brighteners and the attenuation of the fluorescent emission by ink halftones.

Halftone moiré due to imager distortion

Moire in color printing is an undesirable visible artifact that can arise from overlaying multiple halftone color separations. Halftone geometric configurations designed to avoid moire in the overlays strictly require that individual halftone color separations must possess a low degree of relative distortion. However, optical and mechanical errors of multiple imaging systems within a printer usually produce differences between the color planes in the trajectory and placement of the exposure spots. We study color halftone moire due to these optical and mechanical errors for otherwise moire-free halftone configurations. Distortions due to commonly used imaging systems in xerography (i.e., raster output scanners and image bars) are categorized into two classes that depend on the direction of the displacement errors [i.e., process direction distortions (such as shear, bow, and skew) and cross-process direction distortions (such as scanline magnification, magnification imbalance, and high-order scanline distortions)]. Using frequency vector representation of color halftones, we derive analytical expressions for acceptability bounds on these distortions. We evaluate the analytical expressions for a classical halftone screen configuration and a minimum rosette geometry to enable specification allocations for different imaging components in the design of an imaging system.

Constrained Acquisition of Ink Spreading Curves From Printed Color Images

Today's spectral reflection prediction models are able to predict the reflection spectra of printed color images with an accuracy as high as the reproduction variability allows. However, to calibrate such models, special uniform calibration patches need to be printed. These calibration patches use space and have to be removed from the final product. The present contribution shows how to deduce the ink spreading behavior of the color halftones from spectral reflectances acquired within printed color images. Image tiles of a color as uniform as possible are selected within the printed images. The ink spreading behavior is fitted by relying on the spectral reflectances of the selected image tiles. A relevance metric specifies the impact of each ink spreading curve on the selected image tiles. These relevance metrics are used to constrain the corresponding ink spreading curves. Experiments performed on an inkjet printer demonstrate that the new constraint-based calibration of the spectral reflection prediction model performs well when predicting color halftones significantly different from the selected image tiles. For some prints, the proposed image based model calibration is more accurate than a classical calibration.

Ink-dependent <italic>n</italic>-factors for the Yule-Nielsen modified spectral Neugebauer model

Different inks may have different mechanical and/or optical properties. Existing Yule-Nielsen modified Neugebauer spectral prediction models assume however that the inks forming a color halftone behave similarly, i.e. that a single n-factor can model the lateral propagation of light within the paper as well as non-uniformities of the ink dot thickness profiles. However, if the inks have very different optical or mechanical properties, each ink may be separately modeled with its specific n-factor. In order to predict the reflection spectrum of such color halftones, we extend the ink spreading enhanced Yule-Nielsen modified spectral Neugebauer (EYNSN) model by calculating for each halftone an optimal n-factor as an average of the ink specific n-factors weighted by a parabolic function of the ink surface coverages. We compare the prediction accuracies of the standard EYNSN model where each halftone is predicted by making use of one global n-factor with the predictions accuracies of the extended EYNSN model where each halftone is predicted with its corresponding optimal n-factor derived from the individual ink-specific n-factors. For inks having very different optical and/or mechanical properties, we observe an improvement of the prediction accuracies.

Spectral prediction model for color prints on paper with fluorescent additives

I propose a model for predicting the total reflectance of color halftones printed on paper incorporating fluorescent brighteners. The total reflectance is modeled as the additive superposition of the relative fluorescent emission and the pure reflectance of the color print. The fluorescent emission prediction model accounts for both the attenuation of light by the halftone within the excitation wavelength range and for the attenuation of the fluorescent emission by the same halftone within the emission wavelength range. The model's calibration relies on reflectance measurements of the optically brightened paper and of the solid colorant patches with two illuminants, one including and one excluding the UV components. The part of the model predicting the pure reflectance relies on an ink-spreading extended Clapper-Yule model. On uniformly distributed surface coverages of cyan, magenta, and yellow halftone patches, the proposed model predicts the relative fluorescent emission with a high accuracy (mean DeltaE(94)=0.42 under a D65 standard illuminant). For optically brightened paper exhibiting a moderate fluorescence, the total reflectance prediction improves the spectral reflectance prediction mainly for highlight color halftones, comprising a proportion of paper white above 12%. Applications include the creation of improved printer characterization tables for color management purposes and the prediction of color gamuts for new combinations of optically brightened papers and inks.

Interaction between Light, Paper and and Color Halftones: Challenges and Modelization Approaches

We review the phenomena having an impact on the interaction between light, paper and color halftones. They comprise surface reflections and refractions at the air-paper interface, propagation of light within the paper, internal reflections at the paper-air interface, as well as ink spreading and trapping. We introduce basic notions from radiometry and optics, such as the definitions of radiant flux, irradiance, radiance, Lambert reflector, as well as collimated and diffuse light reflection and refraction. We then present classical spectral reflection models, their extension to multi-ink color halftones and the impact of different measuring devices (radiant detector, integrated sphere). Finally we briefly review ink spreading models and highlight the topics deserving further research.

Model-based color halftoning using direct binary search

In this paper, we develop a model-based color halftoning method using the direct binary search (DBS) algorithm. Our method strives to minimize the perceived error between the continuous tone original color image and the color halftone image. We exploit the differences in how the human viewers respond to luminance and chrominance information and use the total squared error in a luminance/chrominance based space as our metric. Starting with an initial halftone, we minimize this error metric using the DBS algorithm. Our method also incorporates a measurement based color printer dot interaction model to prevent the artifacts due to dot overlap and to improve color texture quality. We calibrate our halftoning algorithm to ensure accurate colorant distributions in resulting halftones. We present the color halftones which demonstrate the efficacy of our method.

Spectral reflection and dot surface prediction models for color halftone prints

The proposed new spectral reflection model enhances the classical Clapper-Yule model by taking into account the fact that proportionally more incident light through a given colorant surface is reflected back onto the same colorant surface than onto other colorant surfaces. It comprises a weighted mean between a component specifying the part of the incident light that exits through the same colorant as the colorant from which it enters (Saunderson corrected Neugebauer component) and a component specifying the part of the incident light whose emerging light components exit from all colorants (Clapper-Yule component). We also propose models for taking into account ink spreading, a phenomenon that occurs when printing an ink halftone in superposition with one or several solid inks. The ink-spreading model incorporates nominal-to-effective surface coverage functions for each of the different ink superposition conditions. A system of equations yields the effective ink surface coverages of a color halftone as a weighted mean of the ink surface coverages specific to the different superposition conditions. The new spectral reflection prediction model combined with the ink-spreading model yields excellent spectral reflection predictions for clustered-dot color halftones printed on an offset press or on thermal transfer printers.

Richard Strauss: Autographen, Portrats, Buhnenbilder. Ausstellung zum 50. Todestag (review)

Richard Strauss: Autographen, Portrats, Buhnenbilder. Ausstellung zum 50. Todestag. Edited by Hartmut Schaefer. In Zusammenarbeit mit: Richard-Strauss-Archiv, Garmisch; Theaterwissenschaftliche Sammlung, Universitat zu Koln; Deutsches Theatermuseum, Munchen. Munich: Bayerische Staatsbibliothek, 1999. [336 p. ISBN 3-9802700-4-1. euro34.] Illustrations, color plates, bibliography, index. In the five years that it has taken for this marvelous catalog prepared for the fiftieth anniversary of Richard Strauss's death to reach North American shores, we have arrived at the 140th anniversary of his birth. The exhibition of Strauss holographs (manuscripts, letters), portraits, production materials, and other primary sources documented in this catalog opened at the Bayerisches Staatsbibliothek on 8 September 1999, fifty years to the day after his death. The Bayerisches Staatsbibliothek has long been a collector of Straussiana and currently holds sixty-four music autographs, around two thousand autograph letters and other documents, and many first-edition prints of Strauss's works. For this exhibition, its own collection was augmented by materials loaned by the Richard-Strauss-Archiv in Garmisch. Understandably, there is a certain Munich-centeredness to the catalog, with an essay on the premieres and first performances of Strauss's operas in Munich and documentation of Strauss's concerts in the city between 1894 and 1932, not to mention that section of the exhibition itself devoted to his two periods as a conductor at the Munich Court Opera (1886-89 and 1894-98). The catalog is in two parts: the catalog proper and an introduction consisting of six scholarly essays on aspects of the exhibition. Color facsimiles and halftones are lavishly spread throughout the entire work. In general, the former are reseived for sketch or other autograph material, portraits, and stage or costume designs, with photographs of people and productions reproduced in halftone. Two appendices (a discography of Strauss as a conductor of his own works and a list of Munich premieres and performances during Strauss's lifetime), a bibliography, and an index of proper names conclude the work. There were 642 items in the exhibition. In the catalog, each item is given a detailed description (physical description, library sigla, provenance, etc.), written by Schaefer with the assistance of Sigrid von Moisy, Monika Holl, Roswitha Schlotterer-Traimer, and Reinhold Schlotterer (the latter two also helped choose the items to be displayed). The catalog, and one assumes the exhibition itself, is divided into ten principal sections: biography; original portraits; operas; early works; apprentice works; choral works and melodramas; lieder; tone poems; late works; and Strauss's activity as a conductor at the Munich Court Opera. Each is prefaced by a longer introduction to the general topic. The largest sections, logically, are those devoted to the operas, Strauss's biography, and the tone poems. The biographical section is particularly interesting, as it includes some excurses on areas such as Strauss's relationship with Bayreuth and the Wagner family, his service to the profession through his work to ensure copyright protections for composers, and his leadership in the Allgemeine Deutsche Musikverein. Each of Strauss's operas is discussed, but those works for which the Bayerische Staatsbibliothek owns considerable material (e.g., Guntram, Elektra, Der Rosenhavalier, Arabella, Daphne, and Die liebe der Danae) are treated more exhaustively than those for which it does not (e.g. Feuersnot). In fact, the only noticeable gap in the exhibition's coverage of Strauss's works in general is a lack of discussion of the Alpensinjonie. and the Sinfonia domestica. Throughout the catalog, the annotation is exemplary. Many of the item descriptions are supplemented by excerpts from primary source material such as letters or memoirs, often published for the first lime. …

Colorant-based direct binary search halftoning

Abstract. In this paper, we propose color design criteria for uniformcolor textures, and present a new colorant-based color halftoningtechnique which meets these criteria, and hence generates highquality color halftones. The basic idea behind our halftoning methodis to control the quality of each colorant texture separately alongwith the total dot distribution. In order to achieve this, we first set thetotal dot arrangement and then color the dots optimally without al-tering the total dot arrangement. This corresponds to a constrainedoptimization problem, and we solve this via the swap-only directbinary search heuristic. We employ a luminance human visual sys-tem model to enforce exclusion of visually nonhomogeneous pat-terns for the total dot distribution, as well as for each individual colo-rant texture. Examples of color halftone images generated using ourtechnique are compared to images produced by a plane-independent color halftoning algorithm and by the HP 970 Cx inkjetprinter driver.

<italic>CMYK</italic> Halftoning Algorithm Based on Direct Binary Search

In this paper, we propose color design criteria for uniform color textures, and present a new colorant-based halftoning technique which meets these criteria, and hence generates high quality color halftones. The basic idea behind our halftoning method is to control the quality of each colorant texture separately along with the total dot distribution. In order to achieve this, we first set the total dot arrangement and then color the dots optimally without altering the total dot arrangement. This corresponds to a constrained optimization problem, and we solve this via the swap-only direct binary search (DBS) heuristic. Examples of color halftone images using our technique are compared to images obtained by a plane-independent color halftoning algorithm and by the HP 970 Cx inkjet printer driver.

Look-up table (LUT) method for inverse halftoning

In this paper we propose look-up table (LUT) based methods for inverse halftoning of images. The LUT for inverse halftoning is obtained from the histogram gathered from a few sample halftone images and corresponding original images. The method is extremely fast (no filtering is required) and the PSNR and visual image quality achieved is comparable to the best methods known for inverse halftoning. The LUT inverse halftoning method does not depend on the specific properties of the halftoning method, and can be applied to any halftoning method. Then, an algorithm for template selection for LUT inverse halftoning is introduced. We demonstrate the performance of the LUT inverse halftoning algorithm on error diffused images and ordered dithered images. We also extend LUT inverse halftoning to color halftones.

Extracting color halftones from printed documents using texture analysis

Printed documents often contain text and halftones on the same page. When processing these documents electronically, it is important to separate halftones from text and other illustrations, since their processing requirements differ. We present an algorithm that extracts both grayscale and color halftones from other information on a page. Halftones are commonly produced as a pattern of dots on a uniform lattice. The halftone dot pattern forms an “invisible texture”, producing a spectral component distinct from other information on the page. We show that a single circularly symmetric bandpass filter, tuned to this spectral component, can be used to segment halftones having arbitrary shape and size, even in the presence of image rotations.

Surface Anatomy: The Anatomical Basis of Clinical Examination, 2nd edition, by John S.P. Lumley, 110 pp. 210 color halftones. Edinburgh: Churchill livingstone, 1996. paperback, £13.50

Surface Anatomy: The Anatomical Basis of Clinical Examination, 2nd edition, by John S.P. Lumley, 110 pp. 210 color halftones. Edinburgh: Churchill livingstone, 1996. paperback, £13.50

Reader Response to Color Halftones and Spot Color in Newspaper Design

Reader Response to Color Halftones and Spot Color in Newspaper Design