1. An image-processing apparatus for processing images, comprising: acquiring means for acquiring image signals composed of multiple color components of a 2×2 color-coding array; filtering means for calculating the average of pixel values of any (2n−1) pixels, each including a target pixel and the adjacent pixels having the same color component as that of the target pixel, from the image signals acquired by the acquiring means, and defining the average as a pixel value of the target pixel; and extracting means for extracting the pixel having the average calculated by the filtering means as the pixel value at an extraction rate of 1/(2n−1).