Peter Morovič

HP Labs, Color, Pricinpal Scientist

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I have a background in theoretical computer science and maths, and have specialised in colour and imaging with a broad set of skills in fundamental research and development (input and output colour pipelines) as well as applied development of colour workflow solutions addressing technical gaps and experience centred solution design.

Proven research track record with 40+ refereed journal and conference papers (public and company private), 180+ invention disclosures of which 140+ patent applications (filed or pending) to date.

Specialties: Color science, color reproduction, color vision, image processing, camera pipelines (color correction, color constancy), printing pipelines (separation/halftoning), computational geometry, numerical optimization, mathematical modelling, machine learning.

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Omri Gillath

University of Kansas

Quentin F Stout

University of Michigan

Javier Díaz Noci

Pompeu Fabra University

David Seamon

Kansas State University

Remo Caponi

University of Cologne

Armando Marques-Guedes

UNL - New University of Lisbon

Fabio Cuzzolin

Oxford Brookes University

Lev Manovich

Graduate Center of the City University of New York

Simon Cropper

University of Melbourne

marcello frixione

University of Genova

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Papers by Peter Morovič

The Perceptibility of Color Differences between Thin Lines and its Application to Printing Imaging Pipelines

Color and Imaging Conference

HANS print smoothness optimization and continuous control

Color and Imaging Conference, 2017

HANS3D: A Multi-Material, Volumetric, Voxel-By-Voxel Content Processing Pipeline for Color and Beyond

Color and Imaging Conference, 2017

Color Scrambling for Secure Digital Content Distribution

Revisiting spectral printing: A data driven approach

Spectral printing is a well–established part of imaging that can boast of a rich body of literatu... more Spectral printing is a well–established part of imaging that can boast of a rich body of literature. Nonetheless there has been limited commercial uptake of this approach to visual content reproduction, in spite of its clear benefits. The aim of the present paper is therefore to explore what may lie behind this apparent mismatch by looking at how colorimetric (metameric) and spectral reproduction compare on an 11–ink printing system. To aid the above exploration, the paper proposes a new metric for evaluating spectral reproduction in a visually meaningful way and presents an analysis of the spectral properties of colorimetric and spectral reproductions of a variety of original content including spot colors and fine art. Introduction A key choice when making a print is to decide how it is to relate to original content. This can range from the print becoming the first „original‟ (e.g., fine art created digitally, where its viewing on a display is only an intermediate step of the creative process), via its aim being to please (e.g., holiday snaps) to it being as close to a facsimile as possible (e.g., fine art reproduction, proofing). In the last case, the question arises of how broadly the match needs to hold: only under specific viewing conditions or under any (or a broad range of) lighting and viewing. Here the former is a colorimetric (metameric) reproduction while the latter is a spectral one, which has the benefits of mimicking an original more closely so that looking at it gives the same visual experience as looking at the original would, regardless of where they are viewed and who does the viewing. Conversely, the colorimetric case is set up for specific lighting (typically D50 or D65) and with a specific viewer in mind (usually the 2° CIE Standard Observer) and tends to break down under other conditions (hence its „metameric‟ label). As the case looks very strong for spectral reproduction, it is worth putting two caveats on the table: first, how accurately a spectral match can be achieved and second, how much closer it is to an original than the spectral match obtained when colorimetric matching is set up. The two questions are related in that both spectral and colorimetric reproduction have potentially the same spectral variety at their disposal (being a consequence of the inks, substrate and their interactions) where the difference between an explicit spectral match and the spectral fit of the colorimetrically– selected match may be significantly smaller than the mismatch of either of these to the original reflectance spectrum. In other words, a key question is the spectral „compatibility‟ of the original content and printing system‟s potential. Spectral printing is a topic that can boast of a rich body of literature exploring its various aspects, developing its component building blocks (e.g., spectral capture, printer models (e.g., Taplin 1996), gamut mapping, error metrics for minimization) and applying it in various ways (e.g., fine art reproduction, proofing – including of textiles). Given such a well–established field, it is maybe surprising that it has not found more commercial application and the aim of the present paper is also to look for possible reasons for this fact. Two test cases will therefore be considered: fine art reproduction and spot color proofing, both of which are, in principle, a very good match to the benefits of spectral reproduction. The spectral properties of originals and the way they relate to the spectral variety accessible using two printing setups will then be evaluated. Finally the closest achievable matches will be quantified using an evolution of existing multi–illuminant ∆E metrics that aims to be more representative of an original–reproduction pair being viewed under a broad variety of viewing conditions. Before proceeding with an overview of the state of the art, it may be worth underlining why the above two aspects of spectral characteristics (a physical, „device dependent‟ feature) and perceived difference under a variety of conditions (a psychophysical, „device independent‟ aspect) are considered side by side. The reason for this is that image reproduction is concerned precisely with the interplay between reproduction capabilities and their effects on a viewer – i.e., the device dependent seen in a device independent way. State of the art of spectral match metrics Before turning to the analysis outlined above, two areas of the literature will be reviewed: dimensionality reduction (allowing for an analysis of spectral „compatibility‟) and metrics for evaluating spectral matches. In terms of dimensionality reduction, the basic idea is that the underlying variance in spectral data is often of lower dimensionality than that of the measured reflectance space (i.e., typically having 31D for a 400–700nm range sampled at 10nm steps) and that it can therefore be expressed as a weighted combination of a smaller number of bases. In other words: R=B*w, where R is a…

Generating color lookup table

Method and System to Determine Whether an Image Includes Spatial Adjustments

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.

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

Direct Pattern Control Halftoning of Neugebauer Primaries

IEEE Transactions on Image Processing

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

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Color printing on pre-colored textiles

Color and Imaging Conference

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

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...

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

Structural and Multidisciplinary Optimization

Large-gamut color and spectral display using sub-wavelength gratings

Color and Imaging Conference

PARAWACS: color halftoning with a single selector matrix

Color and Imaging Conference

Computational Print Control

Lecture Notes in Computer Science, 2017

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

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.

A psychovisual study of print smoothness via metameric samples

Color and Imaging Conference

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...

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

Color separation is currently used to decide how much of each available colorant to use for each ... more Color separation is currently used to decide how much of each available colorant to use for each printable color and halftoning then builds patterns that meet those choices. Print color, however, depends not only on how much of each colorant is used, but also on how those colorants are superimposed. Furthermore, there are many halftone patterns that correspond to a given combination of ink amounts. HANS (Halftone Area Neugebauer Separation), which we introduced at last year's IS&T's CIC conference, is a move towards specifying halftone pattern statistics and enables control over print properties beyond their current limits. While the benefits of HANS for color gamut and ink use efficiency have been shown, at this year's NIP, we would like to look more closely at how to determine the set of all possible halftone patterns that match a given color and demonstrate how access to such sets -metamer sets -benefits print control. We will also illustrate how even for a simple CMY ink set, which using current approaches leads to exactly one ink combination per printable color, there are sets of alternative halftone patterns that match a given color. Such sets in turn allow for tradeoffs to be made, e.g., between grain and ink use, even in this simple case.

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Printer management

The Perceptibility of Color Differences between Thin Lines and its Application to Printing Imaging Pipelines

Color and Imaging Conference

HANS print smoothness optimization and continuous control

Color and Imaging Conference, 2017

HANS3D: A Multi-Material, Volumetric, Voxel-By-Voxel Content Processing Pipeline for Color and Beyond

Color and Imaging Conference, 2017

Color Scrambling for Secure Digital Content Distribution