A process for detecting the edges of collimator blades in digital radiography images in the first pass detects the edges of the collimator blades using original image, and the in the second pass repeats edge detection using an image enhanced by a histogram matching technique, for example. The edge detection using an enhanced image may also be repeated any number of times in cases of complex anatomy or when selected radiographic techniques does do not provide sufficient imaging data. The results of the second pass, or the collection of the results of multiple second passes, are then combined with the result from the first pass to form a list of the potential blade edge candidates. A desirable number of edges are then selected from the combined list to form a polygon which encloses the target area of the image, thereby providing the shutter area.