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Color Research

For different illuminants, original (bottom) und copy (top) slightly diverge in color.

We are living in a colorful world, where color is not only an important part of our visual perception but in many cases also an information carrier with significant impact on decisions in our everyday live. More and more frequently, we make these decisions based on copies, if we shop online or using catalogues, for instance.

Unfortunately, the copied world has only little in common with reality.

What are the reasons for that? How can we improve the quality of reproductions?

These questions are investigated by the color group at the Institute of Printing Science and Technology. Modeling and improving imaging systems such as cameras, projectors or printers is not sufficient to comprehensively solve the reproduction problem. A prerequisite is a detailed understanding of the human visual system and considering its multiple properties to adjust the reproduction to human perception.

Our multidisciplinary research covers physical, chemical, mathematical, engineering and psychological aspects related to color reproduction.

For instance, we have developed a spectral copying system that allows reproductions mimicking originals under multiple viewing conditions.

Many sub-problems are still an active research field. One example is the physical modeling of printing systems utilizing many colorants. This requires a detailed knowledge of the interactions between photons, substrate and inks.

Another problem is the typical case, that an output system is physically not capable to reproduce a given image. In what way does an image need to be distorted to allow a reproduction with a minimum of perceptual difference to the original? For determining such reproductions a perception-based image difference measure is required on which we are currently working.

New materials pose new challenges for reproductions. Printed interference effect colors, for instance, change their color depending on the illuminating and viewing geometry. Furthermore, they show distinct texture and glint impression. How many dimensions are required to describe the appearance of such materials? How can we construct an appearance space where the Euclidean distance between two points agrees with their perceived difference? Solutions of such problems have significant impact on tolerance bounds used for reproductions and determine whether a copy is judged to be good or not.

Our vision is to model the complex interaction between physical effects and perception for improving imaging systems and reproduction methods. Our ultimate goal are copies that match with the originals independently of the viewing conditions.