Luminance: A New Visual Feature for Visual Servoing - Visual Servoing via Advanced Numerical Methods - page 67

Chapter 5
Luminance: A New Visual Feature for Visual
Servoing

Christophe Collewet and Eric Marchand

Abstract. 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.

5.1 Introduction

Visual servoing is now a widely used technique in robot control [4]. More generally,
it consists of using information provided by a vision sensor to control the state
of a dynamic system. Robust extraction and real-time spatio-temporal tracking of
visual cues is then usually one of the keys to the success of a visual servoing task.
We will show here that this tracking process can be totally removed and that no