Single step coarse registration and inspection of circular objects

Abstract

A very fast, memory efficient, single-step solution for coarse alignment with determination of angular displacement, and inspection for surface defects on circular objects with non-symmetric patterns and random orientation is described. A suitable geometric partition model of an image is constructed that includes a plurality of spatial bins that can be used for rotation estimation and defect detection. In one embodiment for inspection of circular objects, the geometric partitioning includes 256 spatial bins constituted by concentric circular rings divided into sectors. The number of sectors and thickness of the rings are such that the approximate number of pixels in each region is the same. A set of numbers that encode rotational position and gray level information on the plurality of spatial bins of a reference object are acquired during training and used during run-time wherein the same information relative to a circular object being inspected is computed, and the data are correlated to determine both the coarse rotation and gray level difference in pertinent ones of the plurality of spatial bins.