Ján Morovič

HANS print smoothness optimization and continuous control

Color and Imaging Conference, 2017

Natural color profile adjustment for professionals

While there may be no point in arguing about taste, creative professionals make a living from sha... more While there may be no point in arguing about taste, creative professionals make a living from sharing theirs. Making specific, individual color preferences that a creative professional knows how to achieve when creating content on a display also propagate into print is a significant challenge since it lacks real-time feedback. The present paper introduces a method for allowing creative professionals to use the tools they know and love to also personalize the color behavior of their devices. This is achieved by analyzing color changes applied to images and applying them to a device's ICC profile. As a result the personalized device results in customized color behavior regardless of the workflow used. The paper describes the ICC profile transformation algorithm in detail and provides a color error analysis of its performance.

Color printing on pre-colored textiles

Color and Imaging Conference, 2021

Managing color on a particular imaging system is a wellunderstood challenge with a wealth of exis... more Managing color on a particular imaging system is a wellunderstood challenge with a wealth of existing models, methods and techniques. In the case of printing systems, these tend to operate in the context of a single substrate, where managing color on every additional substrate is approach as a separate, detached problem. While such a mind-set works reasonably well in general, it breaks down when it comes to printing onto precolored textiles, such as pre-dyed fabrics. The present paper therefore introduces a family of approaches that support the use of multiple pre-colored textiles on a given printing system that also allow for a balance between characterization effort and color match accuracy. This, in turn provides solutions that can fit a variety of practical working patterns to maximize overall efficiency and performance.

Real World Metamer Sets: Or How we Came to Love Noise

Color and Imaging Conference, 2021

It is well known that color formation acts as a noise-reducing lossy compression mechanism that r... more It is well known that color formation acts as a noise-reducing lossy compression mechanism that results in ambiguity, known as metamerism. Surfaces that match under one set of conditions-an illuminant and observer or capture device-can mismatch under others. The phenomenon has been studied extensively in the past, leading to important results like metamer mismatch volumes, color correction, reflectance estimation and the computation of metamer sets-sets of all possible reflectances that could result in a given sensor response. However, most of these approaches have three limitations: first, they simplify the problem and make assumptions about what reflectances can look like (i.e., being smooth, natural, residing in a subspace based on some measured data), second, they deal with strict mathematical metamerism and overlook noise or precision, and third, only isolated responses are considered without taking the context of a response into account. In this paper we address these limitati...

A psychovisual study of print smoothness via metameric samples

Color and Imaging Conference, 2019

The smoothness of a print is one of its main image quality attributes. Here smoothness can refer ... more The smoothness of a print is one of its main image quality attributes. Here smoothness can refer to the level of unexpected changes or discontinuities in color transitions (at a macro scale) or the level of local variation (at a micro scale), sometimes also described as grain. This paper starts with presenting an approach to building a first-ever set of metameric printed samples that match in color but vary in grain, followed by a psychovisual study of smoothness perception based on a large number of evaluations by both experts and non-experts. This data shows high levels of intra- and inter-observer correlation and can therefore serve as a robust ground truth for understanding and modelling the print smoothness phenomenon. Then, a previously published predictive smoothness model is revisited, that estimates smoothness from a digital halftone before it is printed, and it is shown to result in high degrees of correlation between observer assigned smoothness judgments and computationa...

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Co-optimization of color and mechanical properties by volumetric voxel control

Structural and Multidisciplinary Optimization, 2019

Controlling the composition of individual voxels allows for a co-optimization of 3D-printed part ... more Controlling the composition of individual voxels allows for a co-optimization of 3D-printed part properties such as color and mechanical ones. As a result, choices can be made continuously about how to use a given system's materials, from favoring mechanical strength to giving preference to color variety. A processing pipeline is presented here that determines the composition of individual print-resolution voxels and exercises control over them in a volumetrically probabilistic way. As a result, it allows for all possible at-voxel contents (liquids, powders, system parameters, etc) to be arranged with all possible local volumetric probabilities. Results are shown here for applying such an approach to a prototype printing testbed for controlling color and mechanical properties as well as their combined domain to produce mechanically strong color parts.

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PARAWACS: color halftoning with a single selector matrix

Color and Imaging Conference, 2016

PARAWACS: color halftoning with a single selector matrix

Color and Imaging Conference, 2016

Direct Pattern Control Halftoning of Neugebauer Primaries

IEEE Transactions on Image Processing, 2017

The associate editor coordinating the review of this manuscript and approving it for publication ... more

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Computational Print Control

Lecture Notes in Computer Science, 2017

Printing may seem like a dinosaur among today’s imaging technologies, since its roots stretch bac... more Printing may seem like a dinosaur among today’s imaging technologies, since its roots stretch back to Becquerel’s work that lead to the first color photographs and the first mechanical color reproduction at the end of the nineteenth century. Ten years ago, we then made the fundamental discovery of a new print control domain, where instead of choices about colorant amounts that are akin to the effect of color filters used since the beginning of color printing, print can be specified by the probabilities of colorant combinations, the Neugebauer Primaries. This has led to the ability to print patterns that were previously inaccessible and consequently, by using large-scale computational optimization, to delivering more color gamut, greater ink use efficiency and greater sharpness and detail in print, while using the same materials and printing system as before. This keynote will present the basic principles of the HANS print control paradigm, review the highlights of results obtained using it to date and indicate its potential future developments.

$Research paper thumbnail of Large color gamut displays with diffraction gratings$

Large color gamut displays with diffraction gratings

Journal of the Optical Society of America A, 2016

The ability to display a broad variety of colors has great benefits not only in the context of en... more The ability to display a broad variety of colors has great benefits not only in the context of entertainment but also as a means to streamline design in prototyping and manufacturing processes. Displays that use RGB filters or backlights cannot span all colors that occur in nature. To improve the accuracy of color reproduction, there have been attempts to include additional color primaries in displays. Existing solutions, however, have an impact on cost, scalability, and spatial resolution and are predominantly applicable to projection systems. We propose an approach based on combining diffraction grating extractors and the HANS imaging pipeline initially developed for printing. This combination offers unprecedented potential to attain large color gamuts with the same backlights commercially used today.

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Color Scrambling for Secure Digital Content Distribution

Traditionally the choices made by color separation are expressed as amounts of each of the availa... more Traditionally the choices made by color separation are expressed as amounts of each of the available colorants to use for each of the reproducible colors. Halftoning then deals with the spatial distribution of colorants, which also results in the nature of their overprinting. However, having a colorant space as the way for color separation to communicate with halftoning gives access only to some of the possible printed patterns that a given printing system is capable of and therefore only to a reduced range of print attributes. In the present paper a method – HANS – is proposed to gain access to all possible, printable patterns by specifying relative area coverages of a printing system’s Neugebauer primaries instead of only colorant amounts. This results in delivering prints with more optimal print attributes than were possible using existing methods, allowing for up to 34% less ink use while delivering a 10% greater color gamut on a test printing system using CMYKcm inks.

HANS – A New Color Separation and Halftoning Paradigm

Traditionally the choices made by color separation are expressed as amounts of each of the availa... more Traditionally the choices made by color separation are expressed as amounts of each of the available colorants to use for each of the reproducible colors. Halftoning then deals with the spatial distribution of colorants, which also results in the nature of their overprinting. However, having a colorant space as the way for color separation to communicate with halftoning gives access only to some of the possible printed patterns that a given printing system is capable of and therefore only to a reduced range of print attributes. In the present paper a method – HANS – is proposed to gain access to all possible, printable patterns by specifying relative area coverages of a printing system’s Neugebauer primaries instead of only colorant amounts. This results in delivering prints with more optimal print attributes than were possible using existing methods, allowing for up to 34% less ink use while delivering a 10% greater color gamut on a test printing system using CMYKcm inks. Introduction Print is the result of a number of colorants of different colors being superimposed on top of a substrate. Since the majority of printing technologies only allow for a very small number of levels of ink to be deposited at a given location on a substrate, halftoning is used to obtain ink patterns that result in a given color when seen from an appropriate viewing distance. These halftone patterns also result in inks being deposited on top of or next to one another in a specific way, giving a color that relates non-linearly to the amounts of the inks used. How much of an ink to use is the result of color separation, where ink amounts are chosen for each printable color. This is preceded by color management, where a choice of color reproduction objective (e.g., accuracy or pleasingness) can be made, where differences between the color gamuts of source content and the destination printing system are dealt with and where a color characterization of a printing system is employed with the aim of accurately rendering the chosen color reproduction objective Early color separation methods for three–ink printing systems, used since the late 19th century, involved the photomechanical construction of halftone patterns by filtering a projection of an original image through a set of color filters, each determining how much of a cyan, a magenta and a yellow ink to use, and then through a halftone screen, which resulted in the formation of dots of proportional sizes on the three printing plates. Here color separation filters determined ink amounts while halftone screens resulted in corresponding per–ink patterns, which were finally superimposed. The effectiveness of such methods was relatively limited given their very indirect control over the resulting printed patterns and therefore colors. Such control was significantly increased when computational color reproduction was pioneered during the first half of the 20th century. Here Neugebauer’s model of halftone color reproduction was key, which in its simplest form states that the color of a halftone pattern is the convex combination of the colors (i.e., CIE XYZs) of the Neugebauer Primaries (NPs) used in it. Here an NP is one of the possible ink overprints, with its convex weight being the relative area covered by it (Fig. 1). Figure 1. Relationship between print materials (top), resulting Neugebauer Primaries (center) for a three–colorant, bi–level printing system and an example of how colorant amounts and Neugebauer Primary area coverages relate in a halftone (bottom). The Neugebauer model enabled much tighter control over a printing system and was used as follows: For each color to be reproduced, find the amounts of inks, which, when halftoned using a given halftoning method, match that color. This involves having a model of the halftoning method, which for given ink amounts predicts corresponding NP area coverages. Having measured the NPs and using the Neugebauer model, a prediction can then be made of the resulting color from the NPs’ colors and their area coverages. Using these two models in reverse, appropriate ink amounts can be obtained for in–gamut colors. Broadly the same principle is employed even in the most recent color separation approaches and halftoning techniques. 10–15 A key to the success of such color separation is the accuracy of the model used and there have been numerous improvements here since the Neugebauer model’s introduction in 1937. In the above approaches, color separation and halftoning communicate via an ink space where color separation determines amounts of inks to use for a given color and halftoning then constructs patterns that deliver them. However, only certain Page 1 of 6

HANS – A New Color Separation and Halftoning Paradigm

Traditionally the choices made by color separation are expressed as amounts of each of the availa... more Traditionally the choices made by color separation are expressed as amounts of each of the available colorants to use for each of the reproducible colors. Halftoning then deals with the spatial distribution of colorants, which also results in the nature of their overprinting. However, having a colorant space as the way for color separation to communicate with halftoning gives access only to some of the possible printed patterns that a given printing system is capable of and therefore only to a reduced range of print attributes. In the present paper a method – HANS – is proposed to gain access to all possible, printable patterns by specifying relative area coverages of a printing system’s Neugebauer primaries instead of only colorant amounts. This results in delivering prints with more optimal print attributes than were possible using existing methods, allowing for up to 34% less ink use while delivering a 10% greater color gamut on a test printing system using CMYKcm inks. Introduction Print is the result of a number of colorants of different colors being superimposed on top of a substrate. Since the majority of printing technologies only allow for a very small number of levels of ink to be deposited at a given location on a substrate, halftoning is used to obtain ink patterns that result in a given color when seen from an appropriate viewing distance. These halftone patterns also result in inks being deposited on top of or next to one another in a specific way, giving a color that relates non-linearly to the amounts of the inks used. How much of an ink to use is the result of color separation, where ink amounts are chosen for each printable color. This is preceded by color management, where a choice of color reproduction objective (e.g., accuracy or pleasingness) can be made, where differences between the color gamuts of source content and the destination printing system are dealt with and where a color characterization of a printing system is employed with the aim of accurately rendering the chosen color reproduction objective Early color separation methods for three–ink printing systems, used since the late 19th century, involved the photomechanical construction of halftone patterns by filtering a projection of an original image through a set of color filters, each determining how much of a cyan, a magenta and a yellow ink to use, and then through a halftone screen, which resulted in the formation of dots of proportional sizes on the three printing plates. Here color separation filters determined ink amounts while halftone screens resulted in corresponding per–ink patterns, which were finally superimposed. The effectiveness of such methods was relatively limited given their very indirect control over the resulting printed patterns and therefore colors. Such control was significantly increased when computational color reproduction was pioneered during the first half of the 20th century. Here Neugebauer’s model of halftone color reproduction was key, which in its simplest form states that the color of a halftone pattern is the convex combination of the colors (i.e., CIE XYZs) of the Neugebauer Primaries (NPs) used in it. Here an NP is one of the possible ink overprints, with its convex weight being the relative area covered by it (Fig. 1). Figure 1. Relationship between print materials (top), resulting Neugebauer Primaries (center) for a three–colorant, bi–level printing system and an example of how colorant amounts and Neugebauer Primary area coverages relate in a halftone (bottom). The Neugebauer model enabled much tighter control over a printing system and was used as follows: For each color to be reproduced, find the amounts of inks, which, when halftoned using a given halftoning method, match that color. This involves having a model of the halftoning method, which for given ink amounts predicts corresponding NP area coverages. Having measured the NPs and using the Neugebauer model, a prediction can then be made of the resulting color from the NPs’ colors and their area coverages. Using these two models in reverse, appropriate ink amounts can be obtained for in–gamut colors. Broadly the same principle is employed even in the most recent color separation approaches and halftoning techniques. 10–15 A key to the success of such color separation is the accuracy of the model used and there have been numerous improvements here since the Neugebauer model’s introduction in 1937. In the above approaches, color separation and halftoning communicate via an ink space where color separation determines amounts of inks to use for a given color and halftoning then constructs patterns that deliver them. However, only certain Page 1 of 6

<title>Data-driven spectral model for color gamut simulation</title>

Color Imaging XIV: Displaying, Processing, Hardcopy, and Applications, 2009

We present a new method to estimate color gamut from primary color spectra only. By using this me... more We present a new method to estimate color gamut from primary color spectra only. By using this method, the number of prints and measurements for printer characterization is greatly reduced, which is of particular importance if there are many ink candidates to be combined. The method consists in building a mapping between primary color spectra and their combinations, based on a training set. The mapping is data-driven, without relying on assumptions based on classic theoretical models. Furthermore, we study the effects of smoothing this mapping and its consequences in color estimation accuracy. We tested the method on recently released Latex-based ink-jet ink, for different pigment and latex loads. The mean simulation accuracy error, optimizing the smoothing parameter, was below 1.5 dE, and gamut estimation error below 2% error. For pigment kinds, mean accuracy was below 4 dE, and gamut estimation error about 5%. In all cases, this new method outperforms other overprint estimation methods, such as Kubelka-Munk.

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Spectral data-driven model for overprint estimation

HANS–Unlocking New Print Control Alternatives By Bringing Color Separation And Halftoning Closer Together

Spectral discrimination of color input devices

Optimizing HANS color separation: meet the CMY metamers

HANS – the Neugebauer Primary based color separation and halftoning print control approach – was ... more HANS – the Neugebauer Primary based color separation and halftoning print control approach – was presented in broad terms at CIC18. The present paper provides an in–depth look at how HANS color separation can be optimized, what level of variety it provides access to and how it can be used for direct optimization of print attributes. The results show that even in the case of having only three colorants – CMY, where current approaches lead to unique solutions, HANS provides significant metamer sets that lead to variety in print attributes such as the 12.7% ink use range show in the results. Introduction Print has many uses, each of which has different requirements in terms of print attributes. Professional photographers tend to focus on image quality, color accuracy and color gamut while print service providers pay close attention to cost and throughput. Architects and engineers care more about line and small text quality for their drawings, while looking for pleasing appearance in prints made of rendered work. The level at which each of a print’s attributes is achieved then depends on the materials used (inks, toners, substrates, varnishes, etc.), on the imaging technology and also on the color separation and halftoning algorithms used. Direct optimization of print attributes and their explicit trading–off is highly desirable, since color resources need to be tuned to individual substrate types and since a single printer model is typically aimed at more than one target use case. Having to tune resources by hand becomes costly and unreliable and also has to deal with the challenges of transitioning between individually chosen colorant combinations (Morovic, 2007). A solution to this problem is the Halftone Area Neugebauer Separation (HANS) approach presented at CIC18 (Morovic et al., 2010), which both gives access to a larger set of printable halftone patterns and allows for explicit optimization of print attributes. While the HANS approach was sketched out previously (Morovic et al., 2011), details of its color separation optimization will first be presented here. A brief summary of HANS will be followed by a detailed exposition of its optimization framework and the paper will conclude with results for the simple case of a printer with CMY inks and a bi–level halftoning mechanism.

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