Halftone Prints Research Articles

Research on information hiding and recognition technology of halftone prints based on mobile phone

This paper studies the method of embedding printing quantum information in the printed image and identifying whether the image carries hidden information by comparing the eigenvalues of the gray-level co-occurrence matrix of the image. The anti-counterfeiting performance of the halftone hidden image after the embedded printed quantum information is analyzed through a combination of subjective and objective methods. The results show that the anti-counterfeiting performance of the image is not affected after the embedded printed quantum information. The encrypted image and the unencrypted image are in the ASM energy, entropy. The difference between differential entropy is obvious. The halftone information hiding algorithm proposed in this paper provides a new idea for realizing the display of halftone hidden information on the mobile terminal.

Characterization and optimization of color attributes chroma (C*) and lightness (L*) in offset lithography halftone print on packaging boards

AbstractThe outcome of a print in production run plays a crucial role in commercial and packaging printing. In the growing packaging industry, colorfulness and saturated prints with high chroma attract the eye of the consumer. The design and layout of a packaging carton comprise of images that consist of halftones in the print process, which demand attractiveness and visibility using bright colors. In this research, an effort has been made to identify and analyze various parameters involved in offset lithography affecting color attributes of prints. This study also focused on the investigation of the best process conditions that would yield optimum color values through multiresponse factors such as chroma and lightness. A general full‐factorial Design of Experiments (DOE) approach was used to evaluate the effect of prepress parameters such as screen ruling and dot shape and press parameters such ink viscosity and paper smoothness. These parameters were then optimized using a customized response surface design. From the experiment, it was observed that viscosity of the ink was a significant factor that majorly controls the color attributes. The surface smoothness of the paperboard was one of the factors influencing the improvement of color reproduction. A smoother surface makes even contact during ink transfer in the offset printing machine and hence reflects color with a higher chroma. The optimum parameters were as follows: 15 Pa s ink viscosity, 0.77 μm paper smoothness, and 200 lines per inch (lpi) screen ruling that resulted in increasing chroma (C*) in the middle and shadow tones in the halftones.

Halo and subsurface scattering in the transparent coating on top of a diffusing material.

Strongly scattering supports coated with thick transparent medium display a bright halo with a characteristic ring shape when illuminated in one point by a thin pencil of light. The halo, whose size is related to the coating thickness, is due to the Fresnel internal reflections of the light scattered by the diffusing support at the coating-air interface. The angular distribution of the reflected light strongly varies over the halo according to the distance from the point initially illuminated, a fact that cannot be observed when a large area of the surface is illuminated as in usual reflectance and bidirectional reflectance distribution function measurements. By considering a Lambertian background and a transparent layer on top of it, both of them being possibly absorbing, we develop a bidirectional subsurface scattering reflectance distribution function model, based on analytical equations and matrix numerical computation, which enables a detailed description of the spatial and angular distribution of the scattered light including the multiple reflections between the background and the coating-air interface. Some applications in which this subsurface scattering phenomenon can be an issue are addressed, such as the reflectance measurement, which can be undervalued when the geometry is not adapted to the coating thickness, or the impact of the phenomenon on heterogeneously colored surfaces such as coated or laminated halftone prints.

Revisited Yule-Nielsen model without fitting of the n parameter.

We introduce a so-called "mean-path-defined Yule-Nielsen" (MPD-YN) model for predicting the color of halftone prints in reflectance or transmittance modes, inspired by the Yule-Nielsen modified spectral Neugebauer model, where the empirical n value is replaced with a spectral parameter different for each halftone, directly calculated thanks to a closed-form formula, a function of the measured spectral reflectances (or accordingly transmittances) of full-tone calibration patches and the surface coverages of the Neugebauer primaries in the halftone. This parameter is based on the average number of internal reflections undergone by light between two half layers of the print, whose expression derives from a flux transfer model between the two half layers. According to the tests carried out in this study with paper printed in inkjet, the predictive performances of the MPD-YN model are rather good and very close to those obtained with the Yule-Nielsen model.

How to design a recto-verso print displaying different images in various everyday-life lighting conditions

This study aims at explaining how to design multi-view prints that can show different images in different illumination conditions. A recent reflectance-transmittance optical model for recto-verso halftone prints is extended in order to fasten the calibration step and is used, according to an inversed approach, to design the recto-verso prints displaying the different images in their respective illumination modes. The good prediction accuracy of the model allows creating special effect prints, such as transformation of a binary image in one mode into a second binary image in the second mode, or the transformation of color image into a grey-level version, or the revelation of a message by texture contrast. Regarding the illumination conditions, simultaneous illumination of both sides of the print is allowed. The difficulty of designing such print comes from the fact that the images that are printed on the two sides of the paper are not the images that are displayed, and that the colors displayable in one mode depend on the colors wanted in the other mode. Since no general color management method for these kinds of prints is available, ad hoc methods are proposed for the different effects considered.

Orientation Modulation for Data Hiding in Chrominance Channels of Direct Binary Search Halftone Prints

Orientation Modulation for Data Hiding in Chrominance Channels of Direct Binary Search Halftone Prints

Orientation Modulation for Data Hiding in Chrominance Channels of Direct Binary Search Halftone Prints

Orientation Modulation for Data Hiding in Chrominance Channels of Direct Binary Search Halftone Prints

Modeling coverage-dependent ink thickness in ink-jet printing

We propose a simple extension of the Murray-Davis halftone reflectance model that accounts for the change of ink dot reflectance due to ink spreading. Significant improvement of the prediction accuracy is obtained for a range of paper substrates and printer combinations compared to the classical Yule-Nielsen and Clapper-Yule models. The results show that ink dot thickness dependency is the main factor limiting the validity of the Murray-Davis model and that optical dot gain can be neglected when the model is calibrated for one specific printer, ink, and substrate combination. The proposed model provides a better understanding of the reflectance from halftone prints that contributes to the development of physical models for simpler and faster printer calibration to different substrates.

Characterizing coated paper surface for modeling apparent dot area of halftone prints.

A new model is proposed for predicting the apparent dot area of simulated halftone prints on coated paper surface without requiring printing. It is based on Hotelling's multivariate T(2) statistic which is shown to provide a measure of lateral light scattering. The T(2) statistic is computed from colorimetric coordinates obtained from of a knife shadow image response on the paper surface. The proposed method offers superior prediction of halftone dot area compared to current light scattering models. A method for characterising peaks on the coated paper surface is introduced in this work. The effect of the paper coating layer thickness and the surface peak height on lateral light scattering and printed dot size are shown.

An automatic method for detecting missing dots in rotogravure printing

We introduce a new approach to detecting missing dots in rotogravure printing, based on binary morphology and convolution filtering, that addresses the drawbacks of automated techniques using a fast Fourier transform algorithm. Our method was developed for the Heliotest, which is a widely used halftone print quality test for rotogravure printing. A strip of decreasing halftone intensity is printed and the missing dots are counted visually. The distance to the 20th missing dot provides the Heliotest print quality number. To automate the determination of the Heliotest number, the strip is scanned with a standard flat-bed scanner. Using image analysis, an image binarization separates the printed dots from the unprinted area. Then, a black and white convolution is performed to locate the specific shape corresponding to the missing dots. Each possible missing dot is analyzed by the algorithm to determine whether it is a missing dot or a dot that is misshapen, weak, or incomplete. We found that this automatic procedure provides an excellent match to visual assessment. On 90 out of 100 test samples used for validation, our method gives the same result as the visual assessment. The other samples have one or two false positives in the missing dots. This was significantly better than the techniques that were in use before. After validation, the technique was deployed at NewPage; it has been regularly used as a product quality test at the mill and at the NewPage Research Center since 2011.

Color changing effects with anisotropic halftone prints on metal

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.

Two-flux transfer matrix model for predicting the reflectance and transmittance of duplex halftone prints.

We introduce a model allowing convenient calculation of the spectral reflectance and transmittance of duplex prints. It is based on flux transfer matrices and enables retrieving classical Kubelka-Munk formulas, as well as extended formulas for nonsymmetric layers. By making different assumptions on the flux transfers, we obtain two predictive models for the duplex halftone prints: the "duplex Clapper-Yule model," which is an extension of the classical Clapper-Yule model, and the "duplex primary reflectance-transmittance model." The two models can be calibrated from either reflectance or transmittance measurements; only the second model can be calibrated from both measurements, thus giving optimal accuracy for both reflectance and transmittance predictions. The conceptual differences between the two models are deeply analyzed, as well as their advantages and drawbacks in terms of calibration. According to the test carried out in this study with paper printed in inkjet, their predictive performances are good provided appropriate calibration options are selected.

Review of spectral reflectance models for halftone prints: Principles, Calibration, and prediction accuracy

AbstractReliable color reproduction can be achieved by establishing, using a model, the correspondence between the spectral reflectance of the printed surface and the amounts of deposited inks. In this article, we review the main models proposed in the literature, recall how each one is calibrated and compare their prediction accuracy for several print sets. The presented models are the Yule‐Nielsen modified spectral Neugebauer model, its cellular instance, the Clapper‐Yule model, its instance supporting low scattering, and the two‐by‐two halftone independent dot centering model. The Yule‐Nielsen and Clapper‐Yule based models are combined with ink spreading assessment methods that account for the interaction between light, inks, and paper. The prediction accuracy of the different models has been tested for several sets of printed colors on different supports, with different printing systems, different inks and different halftoning methods. These results show how the predictive performances and the model parameters vary according to the different printing setups. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 383–397, 2015

Haunting the Streets of Cairo

This article examines connections between visual habits of American imperialism, photographic technology, and biblical imagination in the last decade of the nineteenth century. The author argues that visual habits of optical elision, or the learned technique of not-seeing photographic contemporaries in order to see instead photographic evidence of a biblical past, linked modes of biblical interpretation with forms of American imperialism. She also contends that halftone print technology introduced considerations of the relationship between images and text, providing silhouettes of theological developments at the end of the century that differentiate photography from prior modes of illustration.

Spectral Prediction Model for Halftone Prints by Enhanced Clapper-Yule Model

The classical Clapper-Yule model and its improved models will both introduced the extended application which supports rough printing and halftone color fluorescent imaging. The characteristics of the new model were analyzed and the prospect of the Clapper-Yule mode was discussed. We proposed a new model, which was an enhancement of the classical Clapper-Yule model, which simulate optical dot gain of halftone prints by taking into account lateral scattering within the paper bulk and multiple internal reflections. The model we propose also takes into account the reflectance of inks at surface of the specific colors at specific rates. The model opens the way towards color separation of images to be reproduced. Several designs printed on an offset press demonstrate their applicability and their benefits.

Spectral Prediction Model for Halftone Prints by Enhanced Clapper-Yule Model

The classical Clapper-Yule model and its improved models will both introduced the extended application which supports rough printing and halftone color fluorescent imaging. The characteristics of the new model were analyzed and the prospect of the Clapper-Yule mode was discussed. We proposed a new model, which was an enhancement of the classical Clapper-Yule model, which simulate optical dot gain of halftone prints by taking into account lateral scattering within the paper bulk and multiple internal reflections. The model we propose also takes into account the reflectance of inks at surface of the specific colors at specific rates. The model opens the way towards color separation of images to be reproduced. Several designs printed on an offset press demonstrate their applicability and their benefits.

Yule–Nielsen based recto–verso color halftone transmittance prediction model

The transmittance spectrum of halftone prints on paper is predicted thanks to a model inspired by the Yule-Nielsen modified spectral Neugebauer model used for reflectance predictions. This model is well adapted for strongly scattering printing supports and applicable to recto-verso prints. Model parameters are obtained by a few transmittance measurements of calibration patches printed on one side of the paper. The model was verified with recto-verso specimens printed by inkjet with classical and custom inks, at different halftone frequencies and on various types of paper. Predictions are as accurate as those obtained with a previously developed reflectance and transmittance prediction model relying on the multiple reflections of light between the paper and the print-air interfaces. Optimal n values are smaller in transmission mode compared with the reflection model. This indicates a smaller amount of lateral light propagation in the transmission mode.

Relating halftone dot quality to paper surface topography

Most printed material is produced by printing halftone dot patterns. One of the key issues that determine the attainable print quality is the structure of the paper surface, but the relation is non-deterministic in nature. We examine the halftone print quality and study the statistical dependence between the defects in printed dots and the topography measurement of the unprinted paper. The work concerns SC paper samples printed by an IGT gravure test printer. We have small-scale 2D measurements of the unprinted paper surface topography and the reflectance of the print result. The measurements before and after printing are aligned with subpixel resolution, and individual printed dots are detected. First, the quality of the printed dots is studied using Self Organizing Map and clustering and the properties of the corresponding areas in the unprinted topography are examined. The printed dots are divided into high and low print quality. Features from the unprinted paper surface topography are then used to classify the corresponding paper areas using Support Vector Machine classification. The results show that the topography of the paper can explain some of the print defects. However, there are many other factors that affect the print quality, and the topography alone is not adequate to predict the print quality.

Colors of Halftone Prints Produced with Fluorescent Inks

Colors of Halftone Prints Produced with Fluorescent Inks

Orientation Modulation for Data Hiding in Clustered-Dot Halftone Prints

We present a new framework for data hiding in images printed with clustered dot halftones. Our application scenario, like other hardcopy embedding methods, encounters fundamental challenges due to extreme bilevel quantization inherent in halftoning, the stringent requirements of image fidelity, and other unavoidable printing and scanning distortions. To overcome these challenges, while still allowing for automated extraction of the embedded data and a high embedding capacity, we propose a number of innovations. First, we perform the embedding jointly with the halftoning by employing an analytical halftone threshold function that allows steering of the halftone spot orientation within each halftone cell based upon embedded data. In this process, image fidelity is emphasized and, if necessary, the capability to recover individual data values is sacrificed resulting in unavoidable erasures and errors. To overcome these and other sources of errors, we propose a suitable data detection and error control methodology based upon a statistical representation for the print-scan channel that effectively models the channel dependence upon the cover image gray-level. To combat the geometric distortion inherent in the print-scan process, we exploit the periodic halftone structure to recover from global scaling and rotation and propose a novel decision directed synchronization technique that counters locally varying printing distortion. Experimental results demonstrate the power of the proposed framework: we achieve high operational rates while preserving halftone image quality.