1. An image processing method, comprising: obtaining an input image; enhancing an object in the input image, wherein the act of enhancing the object comprises using a rolling ball filter; and after the object in the input image is enhanced, applying a low-pass filter using a processor to obtain a processed image, wherein the low-pass filter comprises a first parameter that is associated with an image resolution of a volumetric image, and a second parameter that is associated with a slice spacing of the volumetric image.