Novel, fast, edge-directed image reconstruction algorithm using a substepping system for critical-dimension measurement of glass panels

Abstract

We report a system for performing critical-dimension (CD) measurements of glass panels that uses a substepping system to generate a sequence of lower-resolution images and a fast, edge-directed image reconstruction algorithm to combine these images into a higher-resolution image. A large working distance and large aperture of microscope objective is required in glass panel manufacturing, to measure very small distances at high-level repeatability in a short time, which in turn allows only low magnification objectives. Low-resolution images are obtained when the camera of the CD measurement system is moved at step intervals smaller than the normal pixel size of the camera sensor. We propose a fast, edge-directed image registration (IR) algorithm to find the subpixel accuracy information for full-size images to be registered. The number of processed pixels is only about 5% to 10% of the number of pixels in the image, and the algorithm runs noniteratively. Thus, the subpixel IR algorithm is faster than other methods. In addition, a weighting calculation method for fast and robust edge-directed image interpolation algorithm is proposed to form a high-resolution image. Our experimental results prove that the proposed method offers faster processing time than the standard process and acceptable repeatability of CD measurements.