Visual Measurement Method for Transparent Elements Based on Sub-Pixel Image Mosaics

A vision measurement scheme based on sub-pixel image stitching is proposed to solve the problems of unclear features of transparent optical elements, difficulty in the large field of view, and high-precision dimension measurement by machine vision. Furthermore, the rotation angle between the camera coordinate system and the world coordinate system is calibrated in the proposed scheme to obtain accurate scale factors and image-matching results. The rotation angle of the image coordinate system is less than 0. 1 degrees after correction. Additionally, feature matching of transparent components is achieved by adding a grid background. The proposed registration algorithm based on sliding window pre- matching and random sampling consistency to screen the best offset vector increases the image mosaic accuracy to attain 0. 05 pixel, which is significantly improved compared with the previous studies. The scheme is applied to the vision inspection system of transparent optical elements. Under the condition that the moving accuracy is only 0. 02 mm, the image mosaic result with an average error of 0. 12 pixel is obtained, and the large field of view and high-precision size measurement of transparent optical elements are realized.