a method an apparatus for detecting lines in medical images is disclosed , wherein a direction image array and a line image array are formed by filtering a digital image with a single - peaked filter , convolving the resultant array with second order difference operators oriented along the horizontal , vertical , and diagonal axes , and computing the direction image arrays and line image arrays as direct scalar functions of the results of the second order difference operations . advantageously , line detection based on the use of four line operator functions along the horizontal , vertical , and diagonal directions in accordance with the preferred embodiments actually results in fewer computations than line detection based on the use of three line operator functions . in particular , because of the special symmetries involved , 3 × 3 second order difference operators may be effectively used . moreover , the number of computations associated with the second order difference operations may be achieved with simple register shifts , additions , and subtractions , yielding an overall line detection process that is significantly less computationally intensive than prior art algorithms . also according to a preferred embodiment , computational complexity is reduced by selecting a separable single - peaked filter , and sequentially convolving the digital image with the component kernels of the separable single - peaked filter .