A pixel array of an image sensor comprises a chromatic color pixel and an achromatic color pixel. The chromatic color pixel comprises: a first photo diode formed on a substrate; and a color filter formed on an upper part of the first photo diode. The achromatic color pixel is formed on the substrate and comprises a second photo diode having a nano pillar pattern in a surface area of the substrate. Therefore, an optical absorbing rate and a dynamic range of the image sensor can be increased.
