Calibration image pre-processing in 3D body surface measurement system

The three-dimensional (3D) imaging technique based on phase measuring profilometry has numerous advantages in comparison with other structured light techniques. Measurement accuracy is often used as the primary performance index to evaluate three-dimensional imaging systems. To obtain satisfactory accuracy, the error sources are analyzed and the following three methods related to three aspects of the error source are proposed in this paper. Gamma pre-encoding process is used to eliminate gamma distortion of fringe patterns, and multi-frequency heterodyne principle is applied to reduce the influence of skin color and non-uniform reflectivity of the body surface. In addition, a subpixel contour detection based method is proposed, which accurately extracts the edge of elliptical pattern in calibration images. The experimental results show that the root mean square (RMS) error of the measurement system reaches 0.01 mm, and smoother body surface is obtained.