Dark-field microscopic image stitching method for surface defects evaluation of large fine optics

Abstract

One of the challenges in surface defects evaluation of large fine optics is to detect defects of microns on surfaces of tens or hundreds of millimeters. Sub-aperture scanning and stitching is considered to be a practical and efficient method. But since there are usually few defects on the large aperture fine optics, resulting in no defects or only one run-through line feature in many sub-aperture images, traditional stitching methods encounter with mismatch problem. In this paper, a feature-based multi-cycle image stitching algorithm is proposed to solve the problem. The overlapping areas of sub-apertures are categorized based on the features they contain. Different types of overlapping areas are then stitched in different cycles with different methods. The stitching trace is changed to follow the one that determined by the features. The whole stitching procedure is a region-growing like process. Sub-aperture blocks grow bigger after each cycle and finally the full aperture image is obtained. Comparison experiment shows that the proposed method is very suitable to stitch sub-apertures that very few feature information exists in the overlapping areas and can stitch the dark-field microscopic sub-aperture images very well.

Image Stitching for Achilles Tendon Ultrasonography Using Particle Swarm Optimization of Boundary Vector Field Based Similarity and Log-Domain Diffeomorphic Registration

“…The weighted averaging method is performed at the overlap region I 1 ' on the fixed image and the fine-aligned overlap region I 4 ' on the moving image [27][28][29], as shown in figure 3. I s (z) is the intensity at pixel z on the blended image of overlap regions, which is the weighted average of I 1 '(z) and…”

A New Stitching Method for Dark-Field Surface Defects Inspection Based on Simplified Target-Tracking and Path Correction

“…Through sub-aperture scanning and stitching, the dark-field imaging system is able to inspect micrometer-level defects on large optical surfaces of tens of millimeters or even hundreds of millimeters over a relatively short period of time. Compared with other defect inspection methods, such as atomic force microscopy (AFM) and scanning electron microscopy (SEM), this camera-based inspection system presents a good balance between working performance and time consumed (especially for large optics) [11][12][13][14]. Compared with traditional human operators, the camera-based inspection system provides more repeatable and more reliable test results [15].…”

“…In order to obtain more detailed information of the surface defects, the field of view (FOV) of the inspection system should not be very large, usually designed to be several millimeters. Thus, for large optical surfaces, the sub-aperture scanning and stitching method is introduced into the inspection system to obtain the entire distribution of defects [6,7,9,[12][13][14].…”

“…It is also quite time consuming in pixel-level template feature matching calculation. A detailed description of this problem has been discussed by Liu et al in reference [14].…”

Quantitative measurement for the structure of defects on optical surface with lensless Fourier transform digital holographic microscopy

“…Therefore, quantitative measurement for the defects on optical surface with comprehensive information is significantly important for assuring the success of ICF experiment. At present, in engineering, microscopic scattering dark-field imaging technique [4][5][6] is used for measuring the area of the defects on optical surface. Nevertheless, the three-dimensional (3D) structure of defects can't be acquired with this method, which is disadvantageous to the further research and understanding the influence of surface defects on the high-power laser system.…”