An image sensor, comprising: a first sensing region having a first size, configured to sense first kind of light having a first range of wavelengths; and a second sensing region having a second size, configured to sense second kind of light having a second range of wavelengths, wherein the first size and the second size are different, wherein at least portion of the first range of wavelengths and at least portion of the second range of wavelengths are different. The image sensor has a first light sensitivity level for sensing the first kind of light and has a second light sensitivity level for sensing the second kind of light, and a relation between the first size and the second size corresponds to a relation between the first light sensitivity level and the second light sensitivity level.