1. An imaging device, comprising: an imaging optical system which forms a subject image; an imaging element which has a sensitive wavelength region including an infrared wavelength region, and selectively including a visible wavelength region, the imaging element being composed of at least three types of pixels having spectral sensitivities different from each other, and configured to generate original image data including at least three types of original image components to be outputted from each of the pixels by imaging the subject image; and an image processing section, the image processing section including: a dynamic range compressor which compresses a dynamic range based on the original image data for generating dynamic range compressed image data; a luminance signal generator which generates a luminance signal including an infrared wavelength component based on the dynamic range compressed image data; a color signal data generator which generates color signal data based on a visible wavelength component in the original image data; a color-difference signal generator which generates a color-difference signal based on the color signal data; and a color image generator which generates a color image based on the luminance signal and the color-difference signal.