Single step coarse registration and inspection of circular objects

DETAILED DESCRIPTION The present invention provides a very fast, memory-efficient, single-step solution for coarse alignment with determination of object angular displacement, and inspection for surface defects on circular objects with non-symmetric patterns and random angular displacement.
According to the invention, a geometric partitioning of an image includes a plurality of spatial bins or regions for estimating rotation and for defect detection.
In one embodiment for inspection of circular objects the geometric partitioning comprises 256 spatial bins, each bin being a sector of one concentric circular ring of a plurality of concentric circular rings.
The number of sectors and thickness of the rings are such that the approximate number of pixels in each sector is the same.
Angular displacement and grey-level information for a plurality of spatial bins representing 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.
An intensity histogram is optionally generated for the reference object at train-time for comparison with an intensity histogram of the object being inspected.
A spatial histogram of the grey image is also generated during train-time in accordance with the geometric partitioning.
The geometrically partitioned image is of the same size as the grey image of the object being inspected and defines the plurality of spatial bins or regions for purposes of angular displacement determination.
The value of pixels of the grey image for each region are summed and optionally normalized by the number of pixels in each bin.
The simultaneous angular registration or orientation determination and inspection is achieved by deriving data in accordance with the specific geometric partitioning, and the data are aligned and compared to determine both the coarse rotation and grey level difference in pertinent ones of the plurality of spatial bins.
Features of the invention include a highly efficient inspection process with inspection times in the low tens of milliseconds using the single step technique according to the invention, as opposed to prior art implementations that typically require hundreds of milliseconds to run