EMPA Media Technology

Publications 2010

Radial basis function neural networks for modeling growth rates of the basidiomycetes Physisporinus vitreus and Neolentinus lepideus

M. Schubert, S. Mourad, F. Schwarze

A radial basis function (RBF) neural network was developed and compared against a quadratic response surface (RS) model for predicting the specific growth rates of the biotechnologically important basidiomycetous fungi, Physisporinus vitreus and Neolentinus lepideus, under three environmental conditions: temperature (10–30 °C), water activity (0.950–9.998), and pH (4–6). Both the RBF network and polynomial RS model were mathematically evaluated against experimental data using graphical plots and several statistical indices. The evaluation showed that both models gave reasonably good predictions, but the performance of the RBF neural network was superior to that of the classical statistical method for all three data sets used (training, testing, full). Sensitivity analysis revealed that of the three experimental factors the most influential on the growth rate of P. vitreus was water activity, followed by temperature and pH to a lesser extent. In contrast, temperature in particular and then water activity were the key determinants of the development of N. lepideus. RBF neural networks could be a powerful technique for modeling fungal growth behavior under certain parameters and an alternative to time-consuming, traditional microbiological techniques.

Appl. Micorobiol. Biotechnol. 2010 85:703-712

Radial basis function neural networks for modeling growth rates of the basidiomycetes Physisporinus vitreus and Neolentinus lepideus

Aspects of computational geometry in gamut mapping implementations

D. Küpper, K. Simon

Even though gamut mapping (GM) is a three-dimensional polyhedron problem, algorithmically it is usually not treated as such. This is due to tight runtime constraints in practice, which suggest simple algorithms. We will show that basic geometric operations, like the intersection of a ray with the gamut surface, can be implemented very efficiently for typical GM applications that work with device gamuts. This opens up new possibilities to design algorithms without reducing their practicability.

Electronic Imaging 2010: Color Imaging XV: Displaying, Processing, Hardcopy, and Applications.

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Aspects of computational geometry in gamut mapping implementations

Filter methods to preserve local contrast and to avoid artifacts in gamut mapping

M. Meili, D. Küpper, Z, Baranczuk, U. Caluori, K. Simon

Contrary to high dynamic range imaging, the preservation of details and the avoidance of artifacts is not explicitly considered in popular color management systems. An effective way to overcome these difficulties is image filtering. In this paper we investigate several image filter concepts for detail preservation as part of a practical gamut mapping strategy. In particular we define four concepts including various image filters and check their performance with a psycho-visual test. Additionally, we compare our performance evaluation to two image quality measures with emphasis on local contrast. Surprisingly, the most simple filter concept performs highly efficient and achieves an image quality which is comparable to the more established but slower methods.

Electronic Imaging 2010: Color Imaging XV: Displaying, Processing, Hardcopy, and Applications.

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Filter methods to preserve local contrast and to avoid artifacts in gamut mapping

Chapter Gamut Mapping of the book Advances in Imaging and Electron Physics

Z. Baranczuk, J. Giesen, K. Simon, P. Zolliker

The visual system is the dominant component of human perception; an important part of this system is its ability to discriminate colors. Conse- quently, visual information in the form of color images is a natural part of modern communication, particularly on the Internet.

In modern electronic media, information is usually processed (i.e., captured, stored, transformed, and presented) as digital data. As a consequence, such data require a physical device to become visible. Physical devices have restricted color reproduction capabilities, and color scientists refer to the set of colors that a device or a process can present (monitor), reproduce (printer), capture (camera), or store (computer) as the color gamut of the device. Because of device limitations, a printer is typically not able to reproduce all the colors visible on a display screen.

Peter W. Hawkes: Advances in Imaging and Electron Physics, Vol. 160, Burlington: Academic Press, pp. 1-34. ISBN: 978-0-12-381017-5, 2010 Elsevier Inc. Academic Press.

Gamut Mapping

Conjoint Analysis for Evaluating Parameterized Gamut Mapping Algorithms

P. Zolliker, Z. Baranczuk, I. Sprow, J. Giesen

We show that conjoint analysis, a popular multiattribute preference assessment technique used in market research, is a well suited tool to evaluate a multitude of gamut mapping algorithms simultaneously. Our analysis is based on data from psychovisual tests assessed in a laboratory and in a web environment. Conjoint analysis allows us to quantify the contribution of every single parameter value to the perceived value of the algorithm; it also allows us to test the influence of additional parameters like gamut size or color shifts. We show that conjoint analysis can be individualized to images or observers if enough data is available. Especially promising in this respect is the combination of individual and population data.

IEEE Transactions on Image Processing, Vol. 19, No. 3, March 2010

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Conjoint Analysis for Evaluating Parameterized Gamut Mapping Algorithms

Image-Individualized Gamut Mapping Algorithms

Z. Baranczuk, P. Zolliker, J. Giesen

In this article the authors show that image quality measures can be successfully used to develop image-individualized gamut mapping algorithms. First the authors compare different image quality measures for the gamut mapping problem and then validate them using psychovisual data from four recent gamut mapping studies. The scoring function used to validate the quality measures is the hit rate, i.e., the percentage of correct choice predictions on data from psychovisual tests. Some of the image quality measures predict the observer’s preferences as good as scaling methods such as Thurstone’s method, which is used to evaluate the psychovisual tests. This is remarkable because the scaling methods are based on the experimental data, whereas the quality measures are independent of these data. The best performing image quality measure is used to automatically select the optimal gamut mapping algorithm for an individual image.

Journal of Imaging Science and Technology - May/June 2010 - Volume 54, Issue 3, pp. 030201-(7)

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Image-Individualized Gamut Mapping Algorithms

Stochastic modeling of polarized light scattering using a Monte Carlo based stencil method

M. Sormaz, T. Stamm, P. Jenny

This paper deals with an efficient and accurate simulation algorithm to solve the vector Boltzmann equation for polarized light transport in scattering media. The approach is based on a stencil method, which was previously developed for unpolarized light scattering and proved to be much more efficient (speedup factors of up to 10 were reported) than the classical Monte Carlo while being equally accurate. To validate what we believe to be the new stencil method, a substrate composed of spherical non-absorbing particles embedded in a non-absorbing medium was considered. The corresponding single scattering Mueller matrix, which is required to model scattering of polarized light, was determined based on the Lorenz–Mie theory. From simulations of a reflected polarized laser beam, the Mueller matrix of the substrate was computed and compared with an established reference. The agreement is excellent, and it could be demonstrated that a significant speedup of the simulations is achieved due to the stencil approach compared with the classical Monte Carlo.

J. Opt. Soc. Am. A/Vol. 27, No. 5 2010

Stochastic modeling of polarized light scattering using a Monte Carlo based stencil method

Saliency Models as Gamut-Mapping Artifact Detectors

G. Cao, M. Pedersen, Z. Baranczuk

When an image is reproduced with a device different artifacts can occur. These artifacts, if detectable by observers, will reduce the quality of the image. If these artifacts occur in salient regions (regions of interest) or if the artifacts introduce salient regions they contribute to reduce the quality of the reproduction. In this paper we propose a novel method for the detection of artifacts based on saliency models. The method is evaluated against a set of gamut mapped images containing the most common artifacts, which have been marked by a group of color experts. The results have shown that the proposed metrics are promising to detect the artifacts through the reproduction.

CGIV 2010 Final Program and Proceedings

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Saliency Models as Gamut-Mapping Artifact Detectors

Estimation of Backing Influence on Halftone Reflectance

M. Scheller Lichtenauer, H. Hoffstadt, A. Kraushaar, B. Oberhollenzer, P. Zolliker

In the graphic arts industry, there is a need to convert colorimetric readings taken on one backing (usually white) to values that would have been measured with a different backing (usually black). We describe and compare different models for such a conversion. Starting from published models using linear scaling, we developed a new nonlinear model for a strongly scattering substrate. Another new model was derived from the Clapper-Yule model, which includes effects of internal reflectances. All these models are applicable in both the spectral and the tristimulus domain.

For calibration, we used measurements of the bare substrate on both backings. We intentionally make only use of the measured spectral or XYZ values, and do not require knowledge of the nominal CMYK values. This is particularly useful for arbitrary patches measured with a stand-alone measurement device. The test data sets consisted of a large set of test prints, originating from digital or conventional printing processes, and covering typical ranges of mass per area. Both new models outperformed linear regression models and the spectral versions always yielded better results than their corresponding versions in tristimulus space.

CGIV 2010 Final Program and Proceedings

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Estimation of Backing Influence on Halftone Reflectance

Error estimation of paired comparison tests for Thurstone’s Case V

P. Zolliker, Z. Baranczuk

Pair comparison methods based on Case V of Thurstone’s Law of Comparative Judgment are widely used to derive interval scales for perceptual image quality. A thorough treatment of the involved statistical errors is often neglected, even though this is the base for computing confidence intervals and other statistical tests. In this paper we show, that consequent error estimation through all steps of the data analysis provides a simple and reliable method to compute confidence intervals. Monte Carlo simulations are used to verify the results and to compare the proposed error estimation with other known methods.

CGIV 2010 Final Program and Proceedings

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Error estimation of paired comparison tests for Thurstone’s Case V

Segmentation of Images of Lead Free Solder

M. Scheller Lichtenauer, S. Avelar, G. Toporek

We present two approaches to segment metallic phases in images of lead free solder joints. We compare the results of a method without user interaction with another one extrapolating information from a relatively small set of user labeled pixels. The segmented images provide statistical data of spatial characteristics of phases to serve as input in numerical models of solder joints.

Lecture Notes in Computer Science, Springer, Proceedings of ICISP 2010

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Segmentation of Images of Lead Free Solder

Influence of linear birefringence in the computation of scattering phase functions

M. Sormaz, T. Stamm, P. Jenny

Birefringent media, like biological tissues, are usually assumed to be uniaxial. For biological tissues, the influence of linear birefringence on the scattering phase function is assumed to be neglectable. In order to examine this, a numerical study of the influence of linear birefringence on the scattering phase function and the resulting backscattering Mueller matrices was performed. It is assumed that the media consist of spherical scattering particles embedded in a non-absorbing medium, which allows us to employ the Lorenz-Mie theory. In the Monte Carlo framework, the influence of linear birefringence on the components of the electric field vector is captured through the Jones N-matrix formalism. The Lorenz-Mie theory indicates that a given linear birefringence value delta_n has a bigger impact on the scattering phase function for large particles. This conclusion is further supported by Monte Carlo simulations, where the phase function was calculated based on the refractive index once in the ordinary direction and once in the extraordinary one. For large particles, comparisons of the resulting backscattering Mueller matrices show significant differences even for small delta_n values.

Journal of Biomedical Optics 2010, 15(5), Article number 055010 (11 pp)

Influence of linear birefringence in the computation of scattering phase functions

Evaluation of color differences: use of LCD monitor

I. Sprow, T. Stamm, P. Zolliker

The use of LCD monitors as a test platform for the evaluation for perceived color differences is examined. The setup and verification of an accurate color reproduction workflow is presented. As a first application we compare a monitor based color difference test with a corresponding already existing test based on printed samples. In view of the results, we regard this method as a good candidate for extended color perception studies allowing more flexible test setups compared to tests using surface colors.

CIC 2010, 18th Color and Imaging Conference, San Antonio Tx., USA, 8-12 November 2010, 115-120

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Evaluation of color differences: use of LCD monitor

Mapping the journey from home to school: a study on children’s representation of space

E. Thommen, S. Avelar, V. Zbinden Sapin, S. Perrenoud, D. Malatesta

This paper describes a study conducted with 235 children from Brazil and Switzerland. The children, from 5 to 13 years of age, were asked to draw the journey they undertake every day from home to school. The purpose of the study is to understand the relationship between the cognitive development and map-drawing abilities of children in both countries. The maps were analyzed qualitatively by focusing on elements of space representation such as paths and landmarks. The analysis shows that younger children can draw simple topological maps and then move on to egocentric landmarks. Older children can identify and draw more streets and buildings and move on to decentered maps. Country differences are mostly related to local geographic and social particularities. No gender differences were found. Results are discussed in relation to the underlying process in developmental abilities of children.

International Research in Geographical & Environmental Education (2010), 19(3):191-205

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Example of a child's map