An image sensor includes a row driver, a pixel array, an analog-to-digital converter, and an output compensating circuit. The row driver generates a photo-gate control signal, a storage control signal, a transfer control signal, a reset control signal and a row selecting signal. The pixel array includes a plurality of pixels, and each pixel uses a deep trench isolation (DTI) region as a photo gate. The pixel array receives optical signals, converts the optical signals to electric signals, and outputs the electric signals as image signals in response to the photo-gate control signal, the storage control signal, the transfer control signal, the reset control signal, and the row selecting signal. The analog-to-digital converter performs an analog-to-digital conversion on the image signals to generate first signals, and the output compensating circuit compensates the first signals.