tailieunhanh - Advances in Theory and Applications of Stereo Vision Part 3

Tham khảo tài liệu 'advances in theory and applications of stereo vision part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 40 Advances in Theory and Applications of stereo Vision Fig. 4. The pinhole camera model. According to the pinhole model the camera is represented by a small point hole the optical center c and an image plane at a distance F behind the hole Duda Hart 1973 Fig. 4 . This model has a small drawback which is to reverse the images so it is common to replace it by an equivalent one in which the optical center c is located behind the image plane. Then the orthogonal projection that passes through the optical center is called the optical axis. Homogeneous coordinates are suitable to describe the projection process in this model Vince 1995 . First consider the center of coordinates of the real world at the optical center and the following axes z orthogonal to the image plane and the axes X and Y orthogonal and also orthogonal to z. The origin of coordinates in the image plane will be the intersection of the z axes with this plane and the axes ÍÍ and V in the image plane will be orthogonal to each other and parallel to X and Y respectively then the projected coordinates in the image plane LT V S T of a point at .r y z l T will be given by Faugeras 1993 cap. 3 u V s -f 0 0 0 0 -f 0 0 0 0 10 y z 1 m PgM 3 Now we must also take into account all the possible transformations that can happen between the coordinates of a point in the space and a projection in the image plane. Consider a modification of the coordinates system in the image plane a scaling of the axes and a translation. These operations in the 2D space of projections can be represented by H ku 0 tu 0 kv tv 0 0 1 4 so that we can obtain a new matrix Pl H P that takes into account these transformations. The parameters au fku av fkv tu y tv are called the intrinsic parameters and they depend only on the camera itself. Markov Random Fields in the Context of stereo Vision 41 Of course we will probably desire to modify the usable coordinates system in the real world. Often a rotation and a translation of the coordinates .