The image processing procedure of the invention receives mosaic image data and calculates a vertical-direction color difference component with regard to each of pixel columns in the mosaic image data in a vertical direction and a horizontal-direction color difference component with regard to each of pixel rows in the mosaic image data in a horizontal direction. The image processing procedure subsequently selects pixels from the mosaic image data, and compares the sign of the vertical color difference component of the target pixel to the signs of the vertical color difference components of the pixels above and below the target pixel, compare the sign of the horizontal color difference component of the target pixel to the signs of the horizontal color difference components of the pixels to the left and to the right of the target pixel, sets the corresponding edge map value of a corresponding edge map to 1 where the signs in one or more of the comparisons are not equal, and sets the corresponding edge map value of the corresponding edge map to 0 where the signs in all of the comparisons are equal.