Luminance: a new visual feature for visual servoing

This chapter is dedicated to a new way to achieve robotic tasks by 2D visual servoing. Contrary to most of related works in this domain where geometric visual features are usually used, we directly here consider the luminance of all pixels in the image. We call this new visual servoing scheme photometric visual servoing. The main advantage of this new approach is that it greatly simplifies the image pro- cessing required to track geometric visual features all along the camera motion or to match the initial visual features with the desired ones. However, as it is required in classical visual servoing, the computation of the so-called interaction matrix is required. In our case, this matrix links the time variation of the luminance to the camera motions. We will see that this computation is based on a illumination model able to describe complex luminance changes. However, since most of the classical control laws fail when considering the luminance as a visual feature, we turn the visual servoing problem into an optimization one leading to a new control law. Ex- perimental results on positioning tasks validate the feasibility of photometric visual servoing and show its robustness regarding to approximated depths, Lambertian and non Lambertian objects, low textured objects, partial occlusions and even, to some extent, to image content