1. An image processing unit that smoothens a notice pixel of input image data with pixel values of pixels around the notice pixel to reduce noise in the image data, the image processing unit comprising: an edge extraction unit that extracts an edge based on the pixel values of the image data; a region determination unit that determines a region to be processed where a sum of edge intensities of the pixels including the notice pixel becomes greater than or equal to a threshold; and a smoothening unit that changes a smoothening intensity in accordance with a size of the region to be processed to smoothen the notice pixel corresponding to the region to be processed.