1. An apparatus for reducing noise in a digital image, the apparatus comprising: a high pass filtering unit determining an edge region of an input image; a low pass filtering unit performing low pass filtering on a region of the input image determined not to be the edge region thereof by the high pass filtering unit; and a sigma filtering unit performing sigma filtering on the region of the input image determined not to be the edge region by the high pass filtering unit, wherein the low pass filtering unit and the sigma filtering unit perform filtering in parallel, wherein the low pass filtering unit compares an average luminance of pixels existing in a mask used for the low pass filtering with an average luminance of pixels in the input image, and calculates a low pass filtering value when the average luminance of the pixels existing in the mask is larger than the average luminance of the pixels in the input image.