A Visualization Tool for Comparing Paintings and Their Underdrawings

This paper will present a visualization tool for comparing images of paintings. The method starts with two types of images, one showing the color surface, the other the underdrawing the first concept of a painting. The purpose of the tool is to support art historians in understanding differences and similarities of the preliminary sketches and the final painting. The algorithm consists of two consecutive steps. In the first step, the two images are registered with an affine transformation based on manually positioned control points. In the second step, the registered images are combined by replacing the value component of the color image – after conversion to the HSV color space – with the gray values of the infrared image. Several examples illustrate the steps and results of the method. Despite the simplicity of the algorithm, we can show the usefulness of the tool for art historians for identification, localization, and comparison.