Calibration of an LCD projector with pinhole model in active stereovision applications

Abstract

In applications like 3D surfacic reconstruction, it can be interesting to use an active stereovision system. We are working on such a system consisting of a colour camera and a LCD projector. The use of colour is a way to differentiate the patterns emitted towards the scene by the projector. By using the LCD projector to project an image with colour patterns onto the scene, the 3D position of the patterns can be reached: one have to match the location of the patterns in the emitted image with their position in the acquired image. This step needs the knowledge of the geometric calibration parameters of the stereovision system. The LCD projector is connected to the computer and the resulting image is projected onto a graduated plane for the object referential. So, a set of 2D cursor positions p_i (in the referential of the emitted image) can be associated to a set of 3D points Pi (in the object referential). Because the plane is motorized, the set of 3D points can cover all the working space while the 2D positions cover all the screen of the emitted image. Then, the half of the couple of points is used to calculate the calibration parameters by using the Faugeras and Toscani method. Finally, the 3D points which belong to the second half of the couples of points are used. They allow to calculate their theoretic corresponding 2D points in the referential of the emitted image, by using the calibration parameters. The comparison with their practical values, obtained during the acquisition step, shows low errors.