Color variation of the gray balance target as related to color misregistration in multi-angle halftone color printing

This study was to investigate how color variation of a gray balance target was related to color misregistration in the multi-angle halftone color printing process. The dot overlap ping patterns of a gray balance target with 25%, 50% and 75% screen period off-register conditions were simulated on computer; the Neugebauer fractional areas from the ran domly selected thirty-one unit areas were calculated through the application of CAD pro grams and programing. The n-modified Neugebauer equations were then used to predict the colors of the targets and color differences between them. In order to verify the theo retical findings, an experimental study was also conducted. There is no significant color difference between the gray balance targets due to color mis registration. The color differences between the targets due to different dot configurations, both from the mathematical analysis study and the experimental study, are all smaller than one AE value although the color difference within a rosette pattern for an individual unit area can vary as much as 16 AE values. Conclusions: (1) One can not reject the null hypothesis of this study which states that color misregistration will not cause significant color variation in gray balance target in multi-angle color printing; (2) the color variation due to color misregistration on a gray balance target will be so small that it can be negligible for the purpose of being a control target for the multi-angle halftone color printing process

Color and Spectral Mixings in Printed Surfaces

International audienceThe present paper discusses the concept of subtractive color mixing widely used in color hardcopy applications and shows that a more realistic concept would be " spectral mixing " : the physical description of the coloration of light by printed surfaces comes from the mixing of light components selectively absorbed by inks or dyes during their patch within the printing materials. Some classical reflectance equations for continuous tone and halftone prints are reviewed and considered as spectral mixing laws. The challenge of extending these models to new inkless printing processes based on laser radiation is also addressed. Color mixing is a key-concept in color reproduction, either by painting, printing, or displaying. It refers to the observation that a large panel of colors (the color gamut) can be achieved by varying the amount of a limited set of base colors, called primaries. With light emitting systems, the primaries are light sources, often with red, green and blue color, that are either superposed or juxtaposed with a shorter period than the visual acuity. Since the tristimulus values of the produced colors is a linear, additive combination of the tristimulus values of the three primaries, this type of color mixing has been called additive color mixing. This concept, based on Grassman's additivity law, enabled the color matching experiments at the basis of colorimetry [1]. In opposition to the light emitting systems, paintings and printed hardcopies selectively attenuate the incident white light in different proportions according to the wavelength. Layers of primaries, paints or inks, are coated on a reflecting support and play a role of spectral filtering of light. This type of color mixing is improperly called subtractive color mixing [2], by reference to the fact that part of the incident light is removed by filtering, but the tristimulus values of paint or ink mixtures cannot be obtained by combining the tristimulus values of the primaries; it is therefore not a color mixing in the sense of colorimetry. However, the subtractive color mixing is also related to a physical experience, which consists in producing many colors by mixing nonscattering dyes, usually of cyan, magenta and yellow color. According to the Beer-Lambert-Bouguer law [1], the spectral absorption coefficient of the dye mixture, () K λ , is a linear, additive combi-The final publication is available at http://link.springer.co

Diffraction-limited near-IR imaging at Keck reveals asymmetric, time-variable nebula around carbon star CIT 6

We present multi-epoch, diffraction-limited images of the nebula around the carbon star CIT 6 at 2.2 microns and 3.1 microns from aperture masking on the Keck-I telescope. The near-IR nebula is resolved into two main components, an elongated, bright feature showing time-variable asymmetry and a fainter component about 60 milliarcseconds away with a cooler color temperature. These images were precisely registered (~35 milliarcseconds) with respect to recent visible images from the Hubble Space Telescope (Trammell et al. 2000), which showed a bipolar structure in scattered light. The dominant near-IR feature is associated with the northern lobe of this scattering nebula, and the multi-wavelength dataset can be understood in terms of a bipolar dust shell around CIT 6. Variability of the near-IR morphology is qualitatively consistent with previously observed changes in red polarization, caused by varying illumination geometry due to non-uniform dust production. The blue emission morphology and polarization properties can not be explained by the above model alone, but require the presence of a wide binary companion in the vicinity of the southern polar lobe. The physical mechanisms responsible for the breaking of spherical symmetry around extreme carbon stars, such as CIT 6 and IRC+10216, remain uncertain.Comment: 18 pages, 5 figures (one in color), to appear in the Astrophysical Journa

Search for low-mass PMS companions around X-ray selected late B stars

We have observed 49 X-ray detected bright late B-type dwarfs to search for close low-mass pre-main sequence (PMS) companions using the European Southern Observatory's ADONIS (Adaptive Optics Near Infrared System) instrument. We announce the discovery of 21 new companions in 9 binaries, 5 triple, 4 quadruple system and 1 system consisting of five stars. The detected new companions have K magnitudes between 6.5 mag and 17.3 mag. and angular separations ranging from 0.2 and 14.1 arcsec (18-2358 AU).Comment: Accepted for publication in Astronomy and Astrophysic

An evaluation of the primary factors which influence proportionality failure

If practical colorants could be found to meet theoretical requirements then there would be no need for color correction in multi-color printing. Color correction is necessary because the available yellow, magenta, and cyan inks absorb and transmit in all parts of the visible spectrum. It is possible to measure how much these colorants deviate from the ideal with the use of a reflection densitometer. The red, green, and blue filter positions on a densitometer will read the cyan, magenta, and yellow densities respectively. From these densities the amount of color correction necessary to compensate for the inks deficiencies is expressed in terms of percent masking. This is usually computed by the formula: percent mask = highest unwanted density/wanted density. The percent mask is often computed from the densities found when measuring a solid area of a particular colorant. The ratio of unwanted densities to wanted densities is often assumed to remain constant for solids and tints. This is the proportionality rule and is assumed to hold true in what are known as the masking equations (which are the basis for photographic masking for color correction.) The problem is that when a graduated scale of a single color is printed from a light tint to a solid, the proportions of the wanted and unwanted densities do not remain the same for varying tint values and solids. This is known as proportionality failure. This paper deals with the statistical evaluation of the three factors (and the interactions between them) which have been suspected of being the primary causes of this phenomenon. The three factors being tested are solid ink density (ink film thickness), type of paper, and half tone screen ruling. The results indicated that screen ruling was the most important factor for all colors with solid ink density being the next in importance. But the type of paper used was not found to influence proportionality failure, except with magenta ink. This, along with the fact that there was very little proportionality failure in yellow ink, may indicate a certain degree of confusion between proportionality failure and the influence of various factors (including paper) on the \u27purity\u27 of a color. It was shown in this experiment that the optimum printing levels which produce the least amount of proportionality failure were at the lowest solid ink density practical, the finest screen ruling, and on uncoated paper (yellow notwithstanding since it displayed comparatively no proportionality failure.) The implications of these results indicate that certain modifications in color correction methods may be necessary if printing conditions deviate widely from these optimum levels

The 0.4-Mo Eclipsing Binary CU Cancri: Absolute Dimensions, Comparison with Evolutionary Models and Possible Evidence for a Circumstellar Dust Disk

Photometric observations in the R and I bands of the detached M-type double-lined eclipsing binary CU Cnc have been acquired and analysed. The photometric elements obtained from the analysis of the light curves have been combined with an existing spectroscopic solution to yield high-precision (errors<2%) absolute dimensions: M_A=0.4333+/-0.0017 Mo, M_B=0.3980+/-0.0014 Mo, R_A=0.4317+/-0.0052 Ro, and R_B=0.3908+/-0.0094 Ro. The mean effective temperature of the system has been estimated to be Teff=3140+/-150 K by comparing multi-band photometry with synthetic colors computed from model atmospheres. Additionally, we have been able to obtain an estimate for the age (~320 Myr) and chemical composition ([Fe/H]~0.0) of the binary system through its membership of the Castor moving group. With all these observational constraints, we have carried out a critical test of recent stellar models for low-mass stars. The comparison reveals that most evolutionary models underestimate the radius of the stars by as much as 10%, thus confirming the trend observed by Torres & Ribas (2002) for YY Gem and V818 Tau. In the mass-absolute magnitude diagram, CU Cnc is observed to be dimmer than other stars of the same mass. After ruling out a number of different scenarios, the apparent faintness of CU Cnc can be explained if its components are some 10% cooler than similar-mass stars or if there is some source of circumstellar dust absorption. The latter could be a tantalizing indirect evidence for a coplanar (Vega-like) dusty disk around this relatively young M-type binary.Comment: 14 pages, 5 figures, 6 tables. Accepted for publication in A&A. Tables 1 and 2 available in electronic form at the CDS after publicatio