“…A related technique is enhancement of high frequency details (sharpening). A variety of preprocessing techniques for chest radiographs based on local equalization, sharpening and combinations and modifications of these techniques have been proposed [98,41,176,180,218,109,21,230], sometimes not only through software but also by using hardware [23,78]. Nowadays almost all vendors sell digital chest units with a larger dynamic range than conventional units and most vendors automatically preprocess the images with proprietary algorithms.…”