1. An image sensor including: a pixel unit configured to output a bayer pattern by converting an optical signal of a subject into an electrical signal; a vertical interpolation unit configured to generate a vertical binning image by adding or averaging values of vertical pixels of the bayer pattern based on weight information set for each row region of the bayer pattern; a horizontal interpolation unit configured to generate a horizontal binning image by adding or averaging values of horizontal pixels of the bayer pattern based on weight information set for each column region of the bayer pattern; and an image composition unit configured to generate a weight-based binning image by composing the vertical and horizontal binning images.