The Application of direct linear trasformation for two-dimensional cinematography

Abstract

Although three-dimensional motion analysis recently has become popular in biomechanical study, tow-dimensional analysis based on the images obtained through a single camera is still used in biomechanical research because it costs less in the staff, economic, time and equipment necessary for both experiment and calculation. To obtain two-dimensional coordinate from the human body, two principal methods, 4 point method and DLT (direct linear transformation) method, are regularly used. The purpose of this study was to discuss these two methods applied in different filming condition by esimating standard errors. The results showed that the DLT method has a higher accuracy than the 4 point method in two kinds of photographic angles of look side and look down, but delicate care should be paid for perspective errors when human movement lies out calibration plane in the DLT method.