In an image sensor provided on a chip, there are a plurality of photodiodes for receiving light. The photodiodes are disposed in at least two rows which are spaced apart from one another. An elongated photodiode which is at least partially covered by a light shield is used to monitor the photodiodes in the first and second rows. The outputs from image sensor are amplified by first and second amplifiers which are also located on the same chip as the image sensor.