Automatic focus algorithms for TDI X-Ray image reconstruction

摘要

In food industry, most products are checked by X-rays for contaminations.These X-ray machines continuously scan the product passing through. Tominimize the required X-ray power, a Time, Delay and Integration (TDI)CCD-sensor is used to capture the image. While the product moves across thesensor area, the X-ray angle changes during the pass. As a countermeasure,adjusting the sensor shift speed on a single focal plane of the product canbe selected. However, the changing angle result in a blurred image independance to the thickness of the product. This so-called ''laminographiceffect'' can be compensated individually for one plane by inverse filtering.As the plane of contamination is unknown, the blurred image will be inverselyfiltered for different planes, but only one of these images shows thecorrectly focussed object. If the correct image can be found, the planecontaining the contamination is identified. In this contribution wedemonstrate how the correctly focussed images can be found by analyzing theimages of all planes. Different characteristics for correctly and incorrectlyfocussed planes like sharpness, number of objects and edges are investigatedby using image processing algorithms.