EMPA Media Technology

Publications 2007

Improved Calibration of Optical Paper Characteristics by an Adapted Paper-MTF Model

S. Mourad

The calibration of color printers is highly influenced by optical scattering. Light scattered at microscopic level within printed papers induces a blurring phenomenon that affects the linearity of the tone reproduction curve. The induced non-linearity is known as optical dot-gain. Engeldrum and Pridham analyzed its impact on printing by Oittinen’s light scattering model. They determined the scattering and absorption coefficients based on spectral measurements of mere solid patches. Their calibration achieves a good independence from any printing irregularities. However, microscopic knife-edge measurements of Arney et al. showed that the model overestimates the influence of the absorption coefficient. As opposed to Oittinen’s model, our approach intrinsically accounts for laterally scattered light fluxes. This is achieved by an extended three-dimensional Kubelka-Munk model. We describe how to determine our coefficients using a similar calibration approach, which decouples the optical dotgain from other printing influences. Our improved model successfully corrects the observed overestimation and is able to predict Arney’s microscopic measurements.

Journal of Imaging Science and Technology 51(4): 283–292, 2007.

Dotgain

Computing Light Statistics in Heterogeneous Media Based on a Mass Weighted Probability Density Function (PDF) method

P. Jenny, S. Mourad, T. Stamm, M. Vöge, and K. Simon

Based on the transport theory, we present a modeling approach to light scattering in turbid material. It uses an efficient and general statistical description of the material's scattering and absorption behavior. The model estimates the spatial distribution of intensity and the flow direction of radiation, both of which are required, e.g., for adaptable predictions of the appearance of colors in halftone prints. This is achieved by employing a computational particle method, which solves a model equation for the probability density function of photon positions and propagation directions. In this framework, each computational particle represents a finite probability of finding a photon in a corresponding state, including properties like wavelength. Model evaluations and verifications conclude the discussion.

JOSA A, Vol. 24, Issue 8, pp. 2206-2219

Point spread function

Retaining Local Image Information in Gamut Mapping Algorithms

P. Zolliker, K. Simon

Our topic is the potential of combining global gamut mapping with spatial methods to retain the percepted local image information in gamut mapping algorithms. The main goal is to recover the original local contrast between neighboring pixels in addition to the usual optimization of preserving lightness, saturation, and global contrast. Special emphasis is placed on avoiding artifacts introduced by the gamut mapping algorithm itself. We present an unsharp masking technique based on an edge-preserving smoothing algorithm allowing to avoid halo artifacts. The good performance of the presented approach is verified by a psycho-visual experiment using newspaper printing as a representative of a small destination gamut application. Furthermore, the improved mapping properties are documented with local mapping histograms.

Image Processing, IEEE Transactions on Volume 16, Issue 3, March 2007 Page(s):664 - 672

Retaining results

The Kubelka–Munk model and Dyck paths

M. Voege, K. Simon

We present a discrete model for light reflection and transmission of turbid media based on lattice paths. We compare the results with the popular Kubelka-Munk model. We introduce a substitution that allows for a lateral scattering interpretation of the scattering and absorption coefficients. The underlying mathematical structure is governed by Chebyshev polynomials of the second kind.

Journal of Statistical Mechanics: Theory and Experiment, Issue 02, pp. 02018 (2007)

Retaining results

Image-Dependent Gamut Mapping as Optimization Problem

J. Giesen, E. Schuberth, K. Simon, P. Zolliker

We explore the potential of image-dependent gamut mapping as a constrained optimization problem. The performance of our new approach is compared to standard reference gamut mapping algorithms in psycho-visual tests.

IEEE Transactions on Image Processing, Publication Date: Oct. 2007 Volume: 16, Issue: 10 On page(s): 2401-2410

Gamut mapping

Conjoint Analysis to Measure the Perceived Quality in Volume Rendering

J. Giesen, K. Mueller, E. Schuberth, L. Wang, P. Zolliker

Visualization algorithms can have a large number of parameters, making the space of possible rendering results rather high-dimensional. Only a systematic analysis of the perceived quality can truly reveal the optimal setting for each such parameter. However, an exhaustive search in which all possible parameter permutations are presented to each user within a study group would be infeasible to conduct. Additional complications may result from possible parameter co-dependencies. Here, we will introduce an efficient user study design and analysis strategy that is geared to cope with this problem. The user feedback is fast and easy to obtain and does not require exhaustive parameter testing. To enable such a framework we have modified a preference measuring methodology, conjoint analysis, that originated in psychology and is now also widely used in market research. We demonstrate our framework by a study that measures the perceived quality in volume rendering within the context of large parameter spaces.

IEEE Transactions on Visualization and Computer Graphics archive Volume 13, Issue 6 (November 2007), Pages 1664-1671

Skeleton feet