Depth Measurement for the Objects with a Small Height Using Depth-Focus-Based Microscopic Vision System

Based on the depth-focus measurement technique, a height-measuring method for the objects with a small height is proposed. It features a simple hardware structure, a low algorithm complexity and a large measurement depth range. The images at different focusing locations, with clear or unclear regions, are used to help calculating the depth positions of focus plane. An algorithm for evaluating the clear image regions is needed for calculating the depth of focus plane. Hence, a weighted evaluation algorithm for the focusing images is given to calculate the degree of focus. Firstly, according to the measurement principle, the hardware system is designed, and the coordinate frames of each part for calculating the depth of focusing plane are created. An image sequence corresponding to the variations in vertical distances is captured by the system. Secondly, the depth calculation theory is introduced, and the image processing method, using a weighted evaluation principle, is designed. Finally, the performance of the proposed method is tested, with a 1um capturing image gap in vertical direction, and the results show that the weighted evaluation algorithm is effective in depth calculation.