A Sub-Pixel Extraction Method for the Center of the Circular Structure from Spot Array Calibration Target

The imaging measurement system must be calibrated before application. In calibration procedure, sub-pixel center extraction is the crucial step for the final accuracy. In this paper, a new sub-pixel extraction method is proposed. Edge detection at pixel level is obtained using LOG operator, then sub-pixel edge detection is realized using the Facet model. Finally, the least squares ellipse fitting is operated on the sub-pixel edge to determine the sub-pixel center. Experiment on a series of simulated images indicates that this algorithm is able to realize the center location accuracy of 0.01-0.02 pixel, and meets the requirement of sub-pixel level.