Highly Accurate 3-D Position Measurement and Non-Linear Coordinate Transformation

An important preprocess in computer vision is to measure the position of an object and to eradicate lens distortion which hampers the recognition of an object from its image. At first, the slit-ray projection method is investigated and some ideas for increasing measurement accuracy are proposed. A regression to normal distribution is achieved by the least squares method for the pixel positions and their intensities. Because of this, the slit-ray center position can be determined with a high accuracy of 0.05 pixel. A method for correcting the distortion of the slit-ray intensity caused by non-uniform reflection is described. It involves compensating the intensity on the basis of a uniform reference light. Optimum measurement conditions for the slit-ray width and the regression range are obtained by examining the relation between intensity fluctuations and measurement error. In order to increase 3-D measurement accuracy, methods for calibrating various parameters are described. Next, by combining three ideas, i.e., the reference of the shift quantities, the en bloc processing of pixel groups and the separation of the transformation into two directions, non-linear coordinate transformation time is reduced. This is effective for the speedy correction of image distortion.