1. An image sensor, comprising: a) a pixel unit configured to output a bayer pattern by converting an optical signal of a subject into an electrical signal; b) a weight setting unit configured to set first weight information for a first row region and second weight information for a second row region at a first predetermined ratio, and third weight information for a first column region and fourth weight information for a second column region at a second predetermined ratio, wherein the first weight information, the second weight information, the third weight information, and the fourth weight information are based on extracted illuminance information; c) 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 the first and second weight information for the first and second row regions of the bayer pattern, respectively; d) 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 the third and fourth weight information for the first and second column regions of the bayer pattern, respectively; and e) an image composition unit configured to generate a weight-based binning image by composing the vertical and horizontal binning images.