Selective Darkening Filter and Welding Arc Observation for the Manual Welding Process

An optical see-through LCD (GLCD) with a resolution of n x m pixels gives the ability to selectively control the darkening in the welders view. The setup of such a Selective Auto Darkening Filter is developed and its applicability tested. The setup is done by integrating a camera into the welding operation for extracting the welding arc position properly. A prototype of a GLCD taylored for welding is mounted in the welder's view. The extraction of the welding arc position requires an enhanced video acquisition during welding. The observation of scenes with high dynamic contrast is an outstanding problem which occurs if very high differences between the darkest and the brightest spot in a scene occur. The application to welding with its harsh conditions needs the development of supporting hardware. The synchronization of the camera with the flickering light conditions of pulsed welding processes in Gas Metal Arc Welding (GMAW) stabilizes the acquisition process and allows the scene to be flashed precisely if required by compact high power LEDs. The image acquisition is enhanced by merging two different exposed images for the resulting image. These source images cover a wider histogram range than it is possible by using only a single shot image with optimal camera parameters. After testing different standard contrast enhancement algorithm a novel content based algorithm is developed. It segments the image into areas with similar content and enhances these independently.