New software for comparing the color gamuts generated by printing technologies

In the color industry, it is vital to know the color gamut of a given device. Several tools for visualizing and comparing color gamuts are available but they each have some drawbacks. Therefore, the aim of this work was to develop and validate new software for comparing the color gamuts generated by printing devices; we also developed an automated color measurement system. The software simultaneously represents the gamuts in the 3D CIELAB space. It also calculates the Gamut Comparison Index and the volume using two algorithms (Convex Hull and Alpha Shapes). To evaluate the performance of our software, we first compared the results it obtained for the color gamuts with those from other comparison methods such as representation in the CIE 1931 chromaticity diagram or other color spaces. Next, we used Interactive Color Correction in 3 Dimensions (ICC3D) software to compare the gamut representations and volumes. Our software allowed us to identify differences between color gamuts that were not discriminated by other methods. This new software will enable the study and comparison of gamuts generated by different printing technologies and using different printing substrates, International Color Consortium profiles, inks, and light sources, thereby helping to achieve high quality color images.Optics Group (FQM151, University of Granada)University of Granada (pre-doctoral contract, Training Programme for Research Staff, FPU)Funding for open access charge: University of Granada/CBU

N-colour separation methods for accurate reproduction of spot colours

In packaging, spot colours are used to print key information like brand logos and elements for which the colour accuracy is critical. The present study investigates methods to aid the accurate reproduction of these spot colours with the n-colour printing process. Typical n-colour printing systems consist of supplementary inks in addition to the usual CMYK inks. Adding these inks to the traditional CMYK set increases the attainable colour gamut, but the added complexity creates several challenges in generating suitable colour separations for rendering colour images. In this project, the n-colour separation is achieved by the use of additional sectors for intermediate inks. Each sector contains four inks with the achromatic ink (black) common to all sectors. This allows the extension of the principles of the CMYK printing process to these additional sectors. The methods developed in this study can be generalised to any number of inks. The project explores various aspects of the n-colour printing process including the forward characterisation methods, gamut prediction of the n-colour process and the inverse characterisation to calculate the n-colour separation for target spot colours. The scope of the study covers different printing technologies including lithographic offset, flexographic, thermal sublimation and inkjet printing. A new method is proposed to characterise the printing devices. This method, the spot colour overprint (SCOP) model, was evaluated for the n-colour printing process with different printing technologies. In addition, a set of real-world spot colours were converted to n-colour separations and printed with the 7-colour printing process to evaluate against the original spot colours. The results show that the proposed methods can be effectively used to replace the spot coloured inks with the n-colour printing process. This can save significant material, time and costs in the packaging industry

Nuevo software para la comparación de gamas de color

ABSTRACT. In colour industry it is really important to know the colour gamut of a device. Through the comparison of gamuts we can see the effects that the use of different inks, papers, light sources or printing technologies has on the colour obtained. There are several programs that make this comparison, but they have some drawbacks. Therefore, we have developed and validated a software to compare colour gamuts generated by printing devices. Before doing so, we have selected the most suitable procedure to carry out this comparison. The software, programmed in MATLAB, represents the gamuts simultaneously in the 3D CIELAB space by interpolating the most external data of the gamut. It also calculates their volume using two algorithms: Convex Hull and Alpha Shapes. The representation is made by interacting with the buttons on the interface. To validate our software, we have performed a double analysis. On the one hand, we have compared the results obtained from the study of the colour gamuts with our software and those obtained in a previous work with the same data. On the other hand, we have used the program ICC3D to compare the representations of the gamuts superimposed in 3D with those of our program, in addition to the volume obtained. The conclusions obtained after using the two programs were the same. Even so, our program presents some advantages. It allowed us to identify differences between the gamuts that were not discriminated by other methods, obtaining more precise information. The new software will allow the study and comparison of gamuts generated by different printing technologies with different papers, ICC profiles and light sources. RESUMEN. En la industria del color es muy importante conocer la gama de colores de un dispositivo. Mediante la comparación de gamas podemos evaluar el efecto que tiene el uso de distintas tintas, papeles, fuentes de iluminación o dispositivos de impresión en el color obtenido. Existen diversos programas que realizan esta comparación, pero tienen inconvenientes. Por ello hemos desarrollado y validado un software para comparar gamas de color generadas por dispositivos de impresión gráfica. Antes de ello, hemos seleccionado el procedimiento más adecuado para realizar esta comparación. El software, programado en MATLAB, representa las gamas simultáneamente en el espacio 3D CIELAB a partir de la interpolación de los datos más externos de la gama, además de calcular su volumen mediante dos algoritmos: Convex Hull y Alpha Shapes. La representación se realiza a partir de la interacción con los botones de la interfaz. Para validar nuestro software hemos realizado un doble análisis. Por un lado, hemos comparado los resultados obtenidos del estudio de las gamas de color con nuestro software y los obtenidos en un TFG previo con los mismos datos. Por otro lado, hemos usado el programa ICC3D para comparar las representaciones de las gamas superpuestas en 3D con las de nuestro programa, además del volumen obtenido. Las conclusiones tras el uso de los dos programas fueron las mismas, encontrando figuras muy similares. Aun así, nuestro programa presenta algunas ventajas. Este nos permitió distinguir diferencias entre las gamas que mediante otros métodos no se discriminaron, obteniendo información más precisa. El nuevo software va a permitir el estudio y comparación de las gamas generadas por distintos dispositivos de impresión gráfica con distintos sustratos de impresión, perfiles ICC e iluminación

A Color Gamut Description Algorithm for Liquid Crystal Displays in CIELAB Space

Because the accuracy of gamut boundary description is significant for gamut mapping process, a gamut boundary calculating method for LCD monitors is proposed in this paper. Within most of the previous gamut boundary calculation algorithms, the gamut boundary is calculated in CIELAB space directly, and part of inside-gamut points are mistaken for the boundary points. While, in the new proposed algorithm, the points on the surface of RGB cube are selected as the boundary points, and then converted and described in CIELAB color space. Thus, in our algorithm, the true gamut boundary points are found and a more accurate gamut boundary is described. In experiment, a Toshiba LCD monitor's 3D CIELAB gamut for evaluation is firstly described which has regular-shaped outer surface, and then two 2D gamut boundaries (CIE- * * boundary and CIE- * * boundary) are calculated which are often used in gamut mapping process. When our algorithm is compared with several famous gamut calculating algorithms, the gamut volumes are very close, which indicates that our algorithm's accuracy is precise and acceptable

Spectral Gamut Mapping and Gamut Concavity

A spectral gamut-mapping algorithm is introduced that works well for printers with a large number of inks. It finds the best mapping onto the convex hull of the printer spectral gamut while preserving color defined in CIE XYZ as much as possible. The technique employs a non-negative least-square fit. Since the gamut-mapping algorithm depends on the common assumption that the gamut is convex, an experimental study of the degree of gamut concavity is conducted. It finds that there is a significant amount of concavity, and that that the degree does not appear to change much as the number of inks is increased. Finally, the performance of the gamut-mapping algorithm and gamut coverage in spectral space is compared for 3-, 4-, 5- and 6-ink printers using both synthetic ink models and real ink data

Origins of the Ambient Solar Wind: Implications for Space Weather

The Sun's outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its ability to forecast how variations in the solar wind (i.e., fast and slow wind streams) impact the Earth. Although the last few decades have seen significant progress in observations and modeling, we still do not have a complete understanding of the relevant physical processes, nor do we have a quantitatively precise census of which coronal structures contribute to specific types of solar wind. Fast streams are known to be connected to the central regions of large coronal holes. Slow streams, however, appear to come from a wide range of sources, including streamers, pseudostreamers, coronal loops, active regions, and coronal hole boundaries. Complicating our understanding even more is the fact that processes such as turbulence, stream-stream interactions, and Coulomb collisions can make it difficult to unambiguously map a parcel measured at 1 AU back down to its coronal source. We also review recent progress -- in theoretical modeling, observational data analysis, and forecasting techniques that sit at the interface between data and theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue connected with a 2016 ISSI workshop on "The Scientific Foundations of Space Weather." 44 pages, 9 figure

A comparative analysis between the RIT Contrast Resolution Test Target And the Gutenberg Test Target

In addition to color, the other two most important properties that determine quality of reproduction of a printing/imaging system are contrast and resolution. Contrast and resolution limitations of an output device partially define output quality. These limitations can be attributed to various factors such as the screening method used by the RIP, the image transfer method of the output device, the substrates used, and capabilities of the postscript interpreter or a combination of all these factors. This study introduces a new test target for quality evaluation called the Gutenberg Test Target. A comparative analysis between the Gutenberg Test Target and the RIT Contrast Resolution Target has been performed. Both targets have been developed collectively by Dr. Edward Granger and Franz Sigg and both are used to measure the contrast and resolution limitations of an imaging system. The Gutenberg target uses a visual subjective comparison to evaluate overall output quality of an imaging/printing system. On the other hand, the RIT Contrast Resolution Target uses a method of analysis to calculate a Contrast-Resolution-Volume (CRV) value, which then is used as a relative indicator of the reproduction quality of the imaging/printing system. For this study both test targets were printed on a selected imaging /printing system with varying degrees of image deteriorations (Gaussian Blur) applied on the images. The image deteriorations simulated different Modulation Transfer Functions (MTF) for different devices. The printed test targets were analyzed by performing two visual experiments, one for each target, using a number of observers. The generated data from the experiment was used for mathematical analysis and a comparison was made between the two targets. The final analysis and results showed that both targets do a good job in measuring the resolution contrast limitation of the system

Modeling Perceptual Trade-offs for Designing HDR Displays

Display technology has evolved in pursuit of perceptual pleasure by providing realism and visual impact. The endeavor of the evolution has brought HDR displays to the market. HDR displays, which have become the mainstream display technology recently, are considered not only the present but also the future of displays because of their daunting technical goals: A peak luminance of 10,000 cd/m^2 and near-monochromatic primaries. However, both positive and negative prospects in terms of perceptual aspects for future HDR displays coexist. On the positive side, it is expected that HDR displays will provide better image quality and more vivid color. On the negative side, apart from technical barriers such as production cost and power consumption, HDR displays will induce side effects, for example, observer metamerism, which refers to the phenomenon that color matches for one observer result in color mismatches for other observers. This particular side effect could be a severe issue in HDR displays as their narrow-band primaries likely worsen the color mismatches. Hence, critical to the success of future HDR displays is dealing properly with the perceptual trade-offs. In other words, future HDR display designers need to select physical specifications that maximize perceptual benefits while minimizing adverse effects. This dissertation aims at exploring both potentially positive and negative aspects of future HDR displays, using various perceptual assessments. In particular, the dissertation focuses on two physical factors of a display device: peak luminance and chromaticity color gamut, and the effects of the two factors on related human perception: image quality, observer metamerism, and colorfulness. The ultimate goal of this dissertation is to address the related human perception aroused by the physical factors and propose models to help design future HDR displays. In order to achieve the goal, the dissertation first addresses the image quality trade-off relationship between peak luminance and chromaticity color gamut. A psychophysical experiment was used to develop models to predict equivalent image quality under the trade-off between peak luminance and chromaticity gamut as a function of the perceptual attributes lightness and chroma. Second, a novel approach based on a computational evaluation to investigate potential observer metamerism in HDR displays was explored. This research shows how observer metamerism in HDR displays varies with varying peak luminance and chromaticity color gamut. This research aims at developing a straightforward model to predict observer metamerism in HDR displays based on the computational evaluation. Third, a psychophysical experiment to derive a colorfulness scale for very saturated colors is carried out. This experiment focuses on understanding how the sensitivity of the human visual system responds to highly-saturated colors that extend beyond the stimuli studied in previous research. The colorfulness scale would help both advanced lighting system and display system designers. Fourth, the dissertation suggests an evaluation tool devised based on the observer metamerism and colorfulness scale works that can be utilized to determine the physical specification of HDR displays, maximizing perceptually positive effects while minimizing perceptually negative effects at the same time

LOW-ORDER DISCRETE DYNAMICAL SYSTEM FOR H\u3csub\u3e2\u3c/sub\u3e-AIR FINITE-RATE COMBUSTION PROCESS

A low-order discrete dynamical system (DDS) for finite-rate chemistry of H2-air combustion is derived in 3D. Fourier series with a single wavevector are employed to represent dependent variables of subgrid-scale (SGS) behaviors for applications to large-eddy simulation (LES). A Galerkin approximation is applied to the governing equations for comprising the DDS. Regime maps are employed to aid qualitative determination of useful values for bifurcation parameters of the DDS. Both isotropic and anisotropic assumptions are employed when constructing regime maps and studying bifurcation parameters sequences. For H2-air reactions, two reduced chemical mechanisms are studied via the DDS. As input to the DDS, physical quantities from experimental turbulent flow are used. Numerical solutions consisting of time series of velocities, species mass fractions, temperature, and the sum of mass fractions are analyzed. Numerical solutions are compared with experimental data at selected spatial locations within the experimental flame to check whether this model is suitable for an entire flame field. The comparisons show the DDS can mimic turbulent combustion behaviors in a qualitative sense, and the time-averaged computed results of some species are quantitatively close to experimental data