A FLASH system for fast and accurate pattern localization

The needs for accurate and efficient object localization prevail in many industrial applications, such as automated visual inspection and factory automation. Image reference approach is very popular in automatic visual inspection due to its general applicability to a variety of inspection tasks. However, it requires very precise alignment of the inspection pattern in the image. To achieve very precise pattern alignment, traditional template matching is extremely time-consuming when the search space is large. In this paper, we present a new FLASH (Fast Localization with Advanced Search Hierarchy) algorithm for fast and accurate object localization in a large search space. This object localization algorithm is very useful for applications in automated visual inspection and pick-and-place systems for automatic factory assembly. It is based on the assumption that the surrounding regions of the pattern within the search range are always fixed, which is valid for most industrial inspection applications. The FLASH algorithm comprises a hierarchical nearest-neighbor search algorithm and an optical-flow based energy minimization algorithm. The hierarchical nearest-neighbor search algorithm produces a rough estimate of the transformation parameters for the initial guess of the iterative optical-flow based energy minimization algorithm, which provides very accurate estimation results and associated confidence measures. Experimental results demonstrate the accuracy and efficiency of the proposed FLASH algorithm.