A method of processing noise in image data by an image processor having a signal-processing portion converting an image signal from an image sensor into a digital signal and outputting the converted signal as image data for each frame, the image data indicating sets of pixel values each having a brightness at a corresponding one of coordinate points arranged in directions of rows and columns is disclosed. The method includes the steps of: extracting pixel values; deciding pixel value; finding autocorrelation coefficients of pixel values which are less than a first threshold value; and deciding random noise in the image.