EMPA Media Technology

Publications 2006

Doubling the Color Gamut Volume of Ink Jet Prints using a Simple Post-Processing

S. Mourad, C. Kornfeld

We describe a novel coating process for preserving and enhancing color images from ink jet prints. It involves stabilizing the printed image, followed by selective chemical interaction with the inks. The coating provides liquid, gas and UV light protection. It also changes the way light interacts with the original colorants. Untrained viewers (e.g. ordinary consumers) report the coated images appear more photographic than the original ink jet image. They prefer these images to the originals by a wide margin and report that they would pay up to $1.00 per print for them. They describe the colors as more luminous and vibrant. To better understand the reaction of these people we have conducted a small study of the spectral properties of the treated images using standard color calibration prints as test samples. Measurements of the treated samples and their comparisons with untreated samples show the method’s ability to enlarge the gamut’s volume up to at least the double size of the initial color gamut volume.

The 3rd European Conference on Colour in Graphics, Imaging and Vision, Leeds, Great Britain, June 2006.

Gamut doubling

Continuity of gamut mapping algorithms

P. Zolliker, K. Simon

The design of a gamut mapping algorithm (GMA) is always a compromise between preserving different competing aspects such as color, contrast, and lightness. A natural requirement of a GMA is that the algorithmic treatment of this competition has to avoid any additional artifacts such as doscontinuities or oss of contrast. In this word, several common gamut mapping algorithms are studied from this aspect, resulting in the observation that problems with geometric discontinuities are widespread. For the assessment of the phenomena induced by local mapping properties, an algorithmic test is developed and applied. This new test supports both the quality check of existing as well as the deveoplment of new GMAs.

J. Electron. Imaging 15, 013004 (Jan-March 2006).

Color Patches

Adding Local Contrast to Global Gamut Mapping Algorithms

P. Zolliker, K. Simon

This paper deals with the potential of spatial gamut mapping methods as a complement to global 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. As a typical representative for such a spatial mapping concept, we study unsharp masking applied to an image of the difference of the original and the result of a given gamut mapping algorithm. Thereby an edge preserving smoothing algorithm is used to avoid halo artefacts. In our psychophysical experiments every considered gamut mapping algorithm shows a significant gain in preference by our local contrast approach. The presented method can be seen as an additional feature towards an image-to-device gamut mapping design.

The 3rd European Conference on Colour in Graphics, Imaging and Vision, Leeds, Great Britain, June 2006.

Contrast enhancement

Modeling Light Scattering in Paper for Halftone Print

P. Jenny, M. Vöge, S. Mourad, T. Stamm

This paper is concerned with the study and description of light scattering in turbid material such as paper. We present a new modeling approach, which is based on the transport theory. A statistical description for the scattering and absorption behavior inside the material is used to obtain spatial distributions of wavelength dependent photon number density and fluxes. Opposed to previous methods, the new approach can account for complex multi-point statistics of the material properties in an efficient and general way. This is achieved by solving a model equation for photon number density and propagation direction distribution. The present method is able to account for the spacial distribution of specific, wavelength dependent scattering and absorption characteristics. Thereby, it offers a general framework which allows to predict for example the appearance of colors in halftone prints.

The 3rd European Conference on Colour in Graphics, Imaging and Vision, Leeds, Great Britain, June 2006.

Contrast enhancement

A Kernel Approach to Gamut Boundary Computation

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

We present a kernel based method to associate an image gamut given as a point cloud in three-dimensional Euclidean space with a continuous shape. The shape we compute is implicitly given as the zero-set of a smooth function that we compute from the point cloud using an efficient optimization method. The feasibility of our approach is demonstrated on a couple of examples.

Special Session “Color Image Processing” at Eusipco 2006 Florence, Italy

Gamut Blob

A Framework for Image-Dependent Gamut Mapping

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

We treat image-to-device gamut mapping as a multi-criteria optimization problem. Our approach leads to a parameterized mathematical optimization problem that allows to constrain the degree to which ob jectives like contrast preservation, hue preservation, saturation preservation and the continuity of the mapping can be violated while maximizing the device gamut exploitation. We demonstrate the feasibility of our approach on several benchmark image- and device gamuts.

Color Imaging XI: Processing, Hardcopy, and Applications, edited by R. Eschbach and G. Marcu, Proceedings of the SPIE-IS&T Electronic Imaging, SPIE Vol. 6058, (2006).

Gamut Overlapping

Optimized RGB for Image Data Encoding

B. Münch, Ú. Steingrímsson

The present paper discusses the subject of an RGB optimization for color data coding. The current RGB situation is analyzed and those requirements selected which exclusively address the data encoding, while disregarding any application or workflow related objectives. In this context, the limitation to the RGB triangle of color saturation, and the discretization due to the restricted resolution of 8 bits per channel are identified as the essential drawbacks of most of today’s RGB data definitions. Specific validation metrics are proposed for assessing the codable color volume while at the same time considering the discretization loss due to the limited bit resolution. Based on those measures it becomes evident that the idea of the recently promoted e-sRGB definition holds the potential of being qualified as a global RGB data standard without imposing restrictions in regard to feasible surface colors. Optimizing strategies are thus suggested and adapted to the e-sRGB concept focusing on 8 bits per channel. The resulting RGB makes it possible to store a color value to a 32 bit word, yet covering the entire gamut of all existing surface colors at a resolution above the perceptible limit for any color sector, thus satisfying the requirements of a universal RGB which is particularly optimized for color image data encoding.

Journal of Imaging Science and Technology 50(2), 125-138, 2006

Gamut Overlapping