1. A method of processing image data formed of an array of image elements, each image element having a display value, said method comprising the steps of: identifying a set of target image elements having display values within a target range of display values from B min to B max ; identifying a set of low display value image elements having display values below B min ; identifying a set of high display value image elements having display values above B max ; applying a morphological dilation to said set of low display value image elements to generate a dilated set of low display value image elements; applying a morphological dilation to said set of high display value image elements to generate a dilated set of high display value image elements; identifying an intersection set of image elements that are present in both said dilated set of low display value image elements and said dilated set of high display value image elements; and removing from said set of target image elements any image elements also present within said intersection set of image elements to form a modified set of target image elements.