Method for determining a desired image signal range from an image having

Abstract

An image signal representing a radiation image comprising an object image and a background region is converted with a predetermined threshold value into a two-valued system, from which a binary image comprising regions approximately corresponding to the object image and the background region is formed. In cases where only one area makes up the region approximately corresponding to the background region in the binary image, a picture element, which corresponds to the image signal value closest to the threshold value among at least some of the picture elements constituting an edge of the binary image in the region approximately corresponding to the object image, is set as another area making up part of the region approximately corresponding to the background region. Thereby two areas separated by the region approximately corresponding to the object image are formed. Binary images are formed repeatedly with the threshold value being changed sequentially so that the two area forming the region approximately corresponding to the background region expand until they meet each other. The desired image signal range is determined from the image signal components corresponding to the picture elements located in the regions approximately corresponding to the background region, which is formed when the two areas become connected to each other.