Abstract: A 3D information extraction algorithm based on a single image was designed in this paper for the difficulties of this research field, in this algorithm, camera imaging matrix M3x4 was obtained by camera calibration firstly, the pseu do inverse matrix M4X3 was calculated by M3x4，the essence of this computation was solving inconsistent ectuations by least squares approximation, 3D information would be extracted from a single image through M1x3，the result wasshown in a image by projection operator. The result could be used for qualitative analysis (qualitative vision) currently due to the limited information from a single image. The experiment indicates that the extracted object should be coplanar. Moreover, the essential theories of 3D to 2D's projection were deduced, the conclusion of the deduce is that imaging process is an irreversible process.

Key words: Pseudo inverse matrix, 3D information extraction, Single image, Qualitative vision