fact the simplest geometrical case is when the camera image planes are on the same plane. The images may alternatively be converted by reprojection through a linear transformation to be on the same image plane. This is called image rectification. Computer stereo vision with many cameras under fixed lighting is called structure from motion. Techniques using a fixed camera and known lighting are called photometric stereo techniques, or "shape from shading". Computer stereo display Many attempts have been made to reproduce human stereo vision on rapidly changing computer displays, and toward this end numerous patents relating to 3D television and cinema have been filed in the USPTO. At least in the US, commercial activity involving those patents has been confined exclusively to the grantees and licensees of the patent holders, whose interests tend to last for twenty years from the time of filing. Discounting 3D television and cinema (which generally require more than one digital projector whose moving images are mechanically coupled, in the case of IMAX 3D cinema), several stereoscopic LCDs are going to be offered by Sharp, which has already started shipping a notebook with a built in stereoscopic LCD. Although older technology required the user to don goggles or visors for viewing computer-generated images, or CGI, newer technology tends to employ Fresnel lenses or plates over the liquid crystal displays, freeing the user from the need to put on special glasses or goggles. Tests In stereopsis tests (short: stereotests), slightly different images are shown to each eye, such that a 3D image is perceived in case stereovision is present. This can be achieved by means of vectographs (visible with polarized glasses), anaglyphs (visible with red-green glasses), lenticular lenses (visible with the naked eye), or head-mounted display technology. The type of changes from one eye to the other may differ depending on which level of stereoacuity is to be detected. A series of stereotests for selected levels thus constitutes a test of stereoacuity. There are two types of common clinical tests for stereopsis and stereoacuity: random dot stereotests and contour stereotests. Random-dot stereopsis tests use pictures of stereo figures that are embedded in a background of random dots. Contour stereotests use pictures in which the targets presented to each eye are separated horizontally. Random dot stereotests The ability of stereopsis can be tested by, for example, the Lang-Stereotest, which consists of a random-dot stereogram upon which a series