1. A method of classifying image data, the image data relating to a set of pixels forming an image in two dimensions, each pixel having a gray level associated therewith, comprising: for a center pixel, entering gray levels associated with neighboring pixels into a first algorithm to yield a result, the neighboring pixels having a predetermined spatial relationship with the center pixel, the result being indicative of a likelihood that the center pixel is part of a line image; wherein the first algorithm determines that each of a first subset of the neighboring pixels which is radially symmetric around the center pixel differs in gray level from the gray level of the center pixel by less than a predetermined threshold amount.