Since painting with brushes needs precise interaction we measure the surface characteristics of the canvas using a distance sensor which is mounted on the robot arm. Besides working with (slightly) curved canvases this allows us also to compensate for mechanical tolerances of the robot while moving the brush over the canvas. Such tolerances are in the sub-millimeter range but still visible for image styles with long strokes and fine brushes. Due to restrictions in the sensor (color dependency of the precision) we so far measure the distance only before we start painting for the entire canvas.