An image sensor includes at least a first row and a second row of photodiodes, each photodiode being coupled with an associated transistor, each associated transistor including a gate, the first and second row of photodiodes forming a series of 2×2 Bayer-pattern units. In each Bayer-pattern unit, a first photodiode and a second photodiode in the first row are designated respectively as a first green pixel and a blue pixel, and a third photodiode and a fourth photodiode in the second row are designated respectively as a red pixel and a second green pixel, wherein a position of the gate of the transistor associated with the first photodiode relative to the first photodiode and a position of the gate of the transistor associated with the fourth photodiode relative to the fourth photodiode are the same.