In this paper, we propose a technique for automatic-exposure control and synthesis for a wide-dynamic-range sensor based on dual-exposure method. Using the proposed technique, a sensor can adaptively adjust its exposure to widely varying illumination conditions and consequently accomplish an infinite dynamic range in theory. An artificial test bench consisting of a virtual illumination source and its imaging system is introduced to verify the performance of the proposed technique. Simulations show how a wider dynamic range can be achieved by the proposed technique. It is also shown that a VGA-resolution CMOS image sensor developed based on the proposed technique can support up to a 119-dB dynamic range.