An image sensor comprises a first photodiode, a second photodiode, and a deep trench isolation structure. The first photodiode and the second photodiode are each disposed within a semiconductor substrate. The first photodiode is adjacent to the second photodiode. The deep trench isolation structure has a varying depth disposed within the semiconductor substrate between the first photodiode and the second photodiode. The DTI structure extends the varying depth from a first side of the semiconductor substrate towards a second side of the semiconductor substrate. The first side of the semiconductor substrate is opposite of the second side of the semiconductor substrate.