Dr. Ole L. Norberg Profile

Dr. Ole L. Norberg

Senior Lecturer at Umeå Univ

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Publications (7)

Proceedings Article | 24 February 2014 Paper

Extension of Murray-Davies tone reproduction model by adding edge effect of halftone dots

G. M. Atiqur Rahaman, Ole Norberg, Per Edström

Proceedings Volume 9018, 90180F (2014) https://doi.org/10.1117/12.2037754

KEYWORDS: Reflectivity, Image segmentation, Solids, Halftones, Printing, Performance modeling, Frequency modulation, RGB color model, Fermium, Light sources

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Proceedings Article | 3 February 2014 Paper

Microscale halftone color image analysis: perspective of spectral color prediction modeling

G. M. Atiqur Rahaman, Ole Norberg, Per Edström

Proceedings Volume 9015, 901506 (2014) https://doi.org/10.1117/12.2037256

KEYWORDS: Image segmentation, Solids, Halftones, Reflectivity, Frequency modulation, Fermium, Mathematical modeling, Printing, Color prediction, RGB color model

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Proceedings Article | 4 February 2013 Paper

Extending color primary set in spectral vector error diffusion by multilevel halftoning

Ole Norberg, Daniel Nyström

Proceedings Volume 8652, 86520M (2013) https://doi.org/10.1117/12.2005147

KEYWORDS: Printing, Binary data, Color reproduction, Diffusion, Electroluminescence, Neptunium, Reflectivity, Visualization, Visual system, Imaging systems

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Ever since its origin in the late 19th century, a color reproduction technology has relied on a trichromatic color reproduction approach. This has been a very successful method and also fundamental for the development of color reproduction devices. Trichromatic color reproduction is sufficient to approximate the range of colors perceived by the human visual system. However, tricromatic systems only have the ability to match colors when the viewing illumination for the reproduction matches that of the original. Furthermore, the advancement of digital printing technology has introduced printing systems with additional color channels. These additional color channels are used to extend the tonal range capabilities in light and dark regions and to increase color gamut. By an alternative approach the addition color channels can also be used to reproduce the spectral information of the original color. A reproduced spectral match will always correspond to original independent of lighting situation. On the other hand, spectral color reproductions also introduce a more complex color processing by spectral color transfer functions and spectral gamut mapping algorithms. In that perspective, spectral vector error diffusion (sVED) look like a tempting approach with a simple workflow where the inverse color transfer function and halftoning is performed simultaneously in one single operation. Essential for the sVED method are the available color primaries, created by mixing process colors. Increased numbers of as well as optimal spectral characteristics of color primaries are expected to significantly improve the color accuracy of the spectral reproduction. In this study, sVED in combination with multilevel halftoning has been applied on a ten channel inkjet system. The print resolution has been reduced and the underlying physical high resolution of the printer has been used to mix additional primaries. With ten ink channels and halfton cells built-up by 2x2 micro dots where each micro dot can be a combination of all ten inks the number of possible ink combinations gets huge. Therefore, the initial study has been focused on including lighter colors to the intrinsic primary set. Results from this study shows that by this approach the color reproduction accuracy increases significantly. The RMS spectral difference to target color for multilevel halftoning is less than 1/6 of the difference achieved by binary halftoning.

Proceedings Article | 4 February 2013 Paper

Improved spectral vector error diffusion by dot gain compensation

Daniel Nyström, Ole Norberg

Proceedings Volume 8652, 86520L (2013) https://doi.org/10.1117/12.2004403

KEYWORDS: Printing, Diffusion, Reflectivity, Color reproduction, Neptunium, Halftones, Light scattering, Binary data, Spectral resolution, Visualization

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Proceedings Article | 12 February 2007 Paper

Paper whiteness and its effect on the reproduction of colors

Ole Norberg

Proceedings Volume 6492, 64920V (2007) https://doi.org/10.1117/12.703013

KEYWORDS: Visualization, Printing, Ultraviolet radiation, Color reproduction, Reflectivity, Color difference, Visual system, Colorimetry, Light sources, Image processing

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The whiteness level of a printing paper is considered as an important quality measure. High paper whiteness improves the contrast to printed areas providing a more distinct appearance of printed text and colors and increases the number of reproducible colors. Its influence on perceived color rendering quality is however not completely explained. The intuitive interpretation of paper whiteness is a material with high light reflection for all wavelengths in the visual part of the color spectrum. However, a slightly bluish shade is perceived as being whiter than a neutral white. Accordingly, papers with high whiteness values incline toward bluish-white. In paper production, a high whiteness level is achieved by the use of highly bleached pulp together with high light scattering filler pigment. To further increase whiteness levels expensive additives such as Fluorescent Whitening Agents (FWA) and shading dyes are needed. During the last years, the CIE whiteness level of some commercial available office paper has exceeded 170 CIE units, a level that can only be reached by the addition of significant amounts of FWA. Although paper whiteness is considered as an important paper quality criterion, its influence on printed color images is complicated. The dynamic mechanisms of the human visual system strive to optimize the visual response to each particular viewing condition. One of these mechanisms is chromatic adaptation, where colored objects get the same appearance under different light sources, i.e. a white paper appears white under tungsten, fluorescent and day light. In the process of judging printed color images, paper whiteness will be part of the chromatic adaptation. This implies that variations in paper whiteness would be discounted by the human visual system. On the other hand, high paper whiteness improves the contrast as well as the color gamut, both important parameters for the perceived color reproduction quality. In order to quantify the influence of paper whiteness pilot papers with different amount of FWA but in all other respects similar were produced on a small scale experimental paper machine. The fact that only the FWA content changes reduces the influences of other properties separated from the paper whiteness in the evaluation process. A set of images, all having characteristics with the potential to reveal the influence of the varied whiteness level on color reproduction quality, were printed on the pilot papers in two different printers. Prior to printing the test images in the experiment, ICC-profiles were calculated for all the used printer-substrate combinations. A visual assessment study of the printed samples was carried out in order to relate the influence of the paper whiteness level to perceived color reproduction quality. The results show an improved color rendering quality with increased CIE whiteness value up to a certain level. Any further increase in paper whiteness does not contribute to an improved color reproduction quality. Furthermore, the fact that some printing inks are UV blocking while others are not will introduce a non uniform color shift in the printed image when the FWA activation changes. This non uniform color shift has been quantified both for variations in illuminant as well as variations of FWA content in the paper.

Proceedings Article | 29 January 2007 Paper

Color measurements on prints containing fluorescent whitening agents

Mattias Andersson, Ole Norberg

Proceedings Volume 6493, 64930Q (2007) https://doi.org/10.1117/12.704196

KEYWORDS: Spectrophotometry, Light sources, Printing, Ultraviolet radiation, Reflectivity, Graphic arts, Dysprosium, Inkjet technology, Optical filters, Calibration

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Papers with a slightly blue shade are, at least among a majority of observers being perceived as whiter than papers having a more neutral color1. Therefore, practically all commercially available printing papers contain bluish dyes and fluorescent whitening agents (FWA) to give the paper a whiter appearance. Furthermore, in the paper industry, the most frequently used measure for paper whiteness is the CIE-whiteness. The CIE Whiteness formula, does in turn, also favor slightly bluish papers. Excessive examples of high CIE-whiteness values can be observed in the office-paper segment where a high CIE-whiteness value is an important sales argument. As an effect of the FWA, spectrophotometer measurements of optical properties such as paper whiteness are sensitive to the ultraviolet (UV) content of the light source used in the instrument. To address this, the standard spectrophotometers used in the paper industry are equipped with an adjustable filter for calibrating the UV-content of the illumination. In the paper industry, spectrophotometers with d/0 measurement geometry and a light source of type C are used. The graphical arts industry on the other hand, typically measures with spectrophotometers having 45/0 geometry and a light source of type A. Moreover, these instruments have only limited possibilities to adjust the UV-content by the use of different weighting filters. The standard for color measurements in the paper industry governs that measurements should be carried out using D65 standard illumination and the 10^o standard observer. The corresponding standard for the graphic arts industry specify D50 standard illumination and the 2^o standard observer. In both cases, the standard illuminants are simulated from the original light source by spectral weighting functions. However, the activation of FWA, which will impact the measured spectral reflectance, depends on the actual UV-content of the illumination used. Therefore, comparisons between measurements on substrates containing FWA from two instruments having light sources with different UV-content are complicated. In this study, the effect of FWA content in paper on color reproduction has been quantified for an officetype paper. Furthermore, examples are given on how color measurement instruments give different readings when FWA is present. For the purpose of this study and in order to ensure that only the effect of FWA was observed, a set of papers with varying additions of FWA otherwise identical, were produced on a small-scale experimental paper machine. The pilot papers were printed in three different printers. Two spectrophotometers representative to the instruments used in the Graphical Art Industry and the Paper Industry respectively where used to measure the printed papers. The results demonstrate how the use of spectral weighting functions for simulating standard illuminants works properly on nonfluorescent material. However, when FWA is present, disparities in UV content between the light source and the simulated illuminant will result in color differences. Finally, in many printing processes, some of the used inks are UVblocking, this further complicates the effect of FWA in printed material. An example is shown on how different color differences are obtained for different process ink combinations when the amount of FWA added to the paper is varied.

Proceedings Article | 22 March 1999 Paper

HUGIN: a small satellite trying to be intelligent

Vlatko Becanovic, Ulrik Eklund, Sven Grahn, Thomas Lindblad, Rickard Lundin, Clark Lindsey, Olle Norberg, Joakim Waldemark, Karina Waldemark

Proceedings Volume 3728, (1999) https://doi.org/10.1117/12.343073

KEYWORDS: Satellites, Sensors, Cameras, Control systems, Computing systems, Space operations, Image sensors, Sun, Evolutionary algorithms, Neural networks

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