An image sensor having an image acquisition mode and an ambient light sensing mode includes a pixel array having pixel cells organized into rows and columns for capturing image data and ambient light data. Readout circuitry is coupled via column bit lines to the pixels cells to read out the image data along the column bit lines. An ambient light detection ("ALD") unit is selectively coupled to the pixel array to readout the ambient light data and to generate an ambient light signal based on ambient light incident upon the pixel array. Control circuitry is coupled to the pixel array to control time sharing of the pixels cells between the readout circuitry during image acquisition and the ALD unit during ambient light sensing.