An image sensor comprises a first photodiode and a second photodiode having a smaller full-well capacitance than the first photodiode, wherein the second photodiode is adjacent to the first photodiode; a first micro-lens is disposed above the first photodiode and on an illuminated side of the image sensor; a second micro-lens is disposed above the second photodiode and on the illuminated side of the image sensor; and a coating layer disposed on both the first and second micro-lens, wherein the coating layer forms a flat top surface on the second micro-lens and a conformal coating layer on the first micro-lens.