Interdisciplinary projects between the field of art history and digital image analysis brought new aspects in both of the fields. While art historians benefit from new objective analysis methods and improved efficiency, for technicians a new field of application and research was opened.

In this project a computer aided system to analyze underdrawings in medieval paintings was developed. Underdrawings are the basic concept of an artist when he starts the creation of his work of art. A systematic analysis of underdrawings, starting with medieval paintings, yields insights to the practice in painting schools, drawing media, drawing tools, and drawing styles. This new experience is important for both, art historians and conservators.

The technical or engineering goal was to set up the environment for a systematic analysis of underdrawings. To visualize an underdrawing, which is usually hidden by covering pigment layers and therefore invisible to the observer in the visible light spectrum, specific infrared sensors were used. Infrared sensors which are sensitive especially in the spectral range from 1.000 nm to 2.200 nm produce digital images of the underdrawing (infrared reflectograms).

The goal from the research point of view was to investigate image processing methods for analysis of underdrawings. In contrast to other infrared projects our goal was not only to digitize, visualize, and improve images of underdrawings but to analyze the structure of the underdrawings with image processing and pattern recognition methods. The system allows to segment underdrawings from the background, analyze strokes in the drawings with respect to drawing tool and drawing material used, and it further allows to differentiate between freehand drawings and drawings created by the help of stencils.