A method to extract irradiation field areas in an X-ray image represented by a digital signal representation comprising the steps of segmenting the image in multiple regions of pixels which have similar local image characteristics, fitting line segments to the boundaries of these regions whereby said line segments correspond with candidate irradiation field boundaries and constitute a segmentation map, classifying regions in said segmentation map into at least two classes, one class being irradiation field and the other class being collimated region on the basis of at least one of local, regional and global image characteristics.