Chromaticity Gamut Enhancement by Heptatone Multi-Color Printing

The present paper studies the chromaticity gamut of multi-color printing processes. Heptatone (7-color) printing - the most promising variant of multi-color printing - offers a significantly larger gamut than a conventional CMYK printing process, approaching CRT and film gamuts. The behavior of the process in the device-independent CIE-XYZ and CIE-L*u*v* colorimetric spaces is explored using the compound Neugebauer model developped for this purpose. A simple and straightforward Moiri-free separation process is proposed. The strong point of the proposed separation process is the fact that only 3 different screen layers are needed for any odd number of basic colors including black

Pseudo-Random Halftone Screening for Colour and Black&White Printing

The idea of using pseudo-random spatial structures in graphic arts (color and black & white rendering algorithms) was suggested by psychologists and biologists about ten years ago. They observed that some natural pseudo-random structures such as the spatial distribution of receptors in the human retina play an important part in the perceptual process. Our modelization of pseudo-random spatial structures resembles the retinal mosaic. It starts by obtaining the quasi-random distribution of tile centers according to some well-defined spectral characteristics. We then obtain the desired tesselation of the output device space by applying the Voronoi polygonization process. Two slightly different approaches to the output image computation are being explored. In the first approach, an analytic black-dot curve is calculated according to the resampled input signal level and the area of each given tile. This analytic curve is scan-converted to obtain the blackened pixels. In the second approach, we associate threshold values to all pixels inside every tile according to some specially tailored analytic spot function. Then, the standard threshold comparison process is applied

An interface for the interactive design of artistic screens

The article presents the concepts and the tools involved in the interactive design of artistic screens. The screen elements are derived from a small set of analytical contours provided by the screen designer. We present the requirements that these contours must satisfy in order to generate consistent screens. Software tools have been developed which provide automatic means for verifying and enforcing these constraints. They include a way of specifying the periodicity of the screen dot and a graphical interface offering a convenient way of specifying and tuning the growth of the screen do

Grid-based method for predicting the behaviour of colour printers

A new grid-based method is proposed for predicting the behaviour of colour printers. The method takes into account the varying density of dots as well as the light diffusion in the paper by defining at different intensity levels different colorimetric values for the printed ink as well as for the paper white. Since the model integrates both the varying density of partly overlapping ink dots and the light diffusion in the underlying substrate, the obtained predictions are more accurate than those obtained with surface based colour prediction methods described in the literature

Specifying color differences in a linear color space (LEF)

This work presents a novel way of generating color differences for synthesizing artistically screened color images. A single color is specified by interacting with the mouse alternately on a constant luminance plane and on a constant hue plane within the LEF color space (the orthogonal space formed by the RGB cube's black-white axis (L) and by its E and F chrominance axes). By interactively selecting a second color point, a color difference is specified. We present a method for extrapolating this color difference throughout all colors of the RGB cube so as to generate consistent color differences, i.e. smoothly varying similar color differences for different colors. The produced artistically screened color patches show that significant luminance differences always generate significant visually perceived differences, whereas significant hue and/or saturation differences do not always generate significant visually perceived differences

Dithering algorithms for variable dot size printers

Dither-based methods for the halftoning of images on multi-level printing devices such as multi-level inkjet printers are presented. Due to the relatively large size of single droplets, halftoning algorithms are still needed. However, since halftoning occurs between the basic levels attainable by printing one, two or several droplets at the same position, artefacts are less visible than in equal resolution bilevel printers. When dithering algorithms are used for the halftoning task, the dither threshold tiles should have oblique orientations so as to make the halftoning artifacts less visible. They should be designed so as to break up the inherent artifacts of variable dot size printers, such as for example continuous lines made up of elongated elliptic dots. The resulting visual effects are shown by simulating the printed dots of a multilevel inkjet printe

Two approaches in scanner-printer calibration: colorimetric space-based vs. "closed-loop"

Studies two different table-based approaches for the calibration of electronic imaging systems. The first approach, which is the classical one, uses the device-independent CIE-XYZ colorimetric space as an intermediate standard space. Input and output devices such as scanners, displays and printers are calibrated separately with respect to the objective CIE-XYZ space. The calibration process requires establishing a 3D mapping between a scanner's device-dependent RGB space and a device-independent colorimetric space such as CIE-XYZ. Measured samples belonging to the calibration set are used for splitting the colorimetric space into Delaunay tetrahedrons. The second approach, the so-called “closed-loop” approach, directly calibrates scanner-printer pairs, without any reference to an objective colorimetric space. It enables a 3D mapping to be built between the scanner's RGB space and the printer's CMY space without requiring any colorimetric measurement. It offers very accurate calibrated output for input samples having the same characteristics (halftone dot, ink spectral reflectance) as the printed samples used for the calibration process. When the desktop scanners' RGB sensibilities are not a linear transform of the CIE x¯,y¯,z¯ matching curves, an accurate calibration can only be made if input color patches are based on the same primary inks as the patches used for device calibratio

How natural forest conversion affects insect biodiversity in the Peruvian Amazon : can agroforestry help?

The Amazonian rainforest is a unique ecosystem that comprises habitat for thousands of animal species. Over the last decades, the ever-increasing human population has caused forest conversion to agricultural land with concomitant high biodiversity losses, mainly near a number of fast-growing cities in the Peruvian Amazon. In this research, we evaluated insect species richness and diversity in five ecosystems: natural forests, multistrata agroforests, cocoa agroforests, annual cropping monoculture and degraded grasslands. We determined the relationship between land use intensity and insect diversity changes. Collected insects were taxonomically determined to morphospecies and data evaluated using standardized biodiversity indices. The highest species richness and abundance were found in natural forests, followed by agroforestry systems. Conversely, monocultures and degraded grasslands were found to be biodiversity-poor ecosystems. Diversity indices were relatively high for all ecosystems assessed with decreasing values along the disturbance gradient. An increase in land use disturbance causes not only insect diversity decreases but also complete changes in species composition. As agroforests, especially those with cocoa, currently cover many hectares of tropical land and show a species composition similar to natural forest sites, we can consider them as biodiversity reservoirs for some of the rainforest insect species