a 50 mm lens 104 the pinhole camera is positioned after the first beam splitter 151 the aperture of the pinhole camera is f 12 the pinhole camera 103 is focused on the foreground plane 162 because acquiring a correct matte is more important than correctly reconstructing the background the foreground and background cameras have f 1 6 apertures and are positioned after the second beam splitter 152 although each camera receive only half the light of the pinhole camera the relative large apertures acquire a relatively large amount of illumination therefore the exposure for these two cameras 101 102 is shorter than the exposure for the pinhole camera as long as the acquired images are not under exposed or over exposed the color calibration process corrects remaining intensity differences between cameras the cameras are calibrated to within a few pixels calibration is maintained by software the optical axes are aligned to eliminate parallax between cameras because the focus is different for the different cameras the acquired images are of different sizes we correct for this with an affine transformation we color correct the images by solving a similar problem in color space here the feature points are the colors of an image of a color chart and the affine transformation is a color.