Fast focusing methods and devices for multi-spectral imaging are disclosed. The clock signal switching circuit includes a first selector that selects one of the clock signals according to the level of a selection signal, a second selector that selects one of first and second control signals according to the level of the selection signal. Because the system can be utilized during a ship’s transport, a positive detection of fissile material can be made and acted upon while the ship is still at sea far from the destination port, where detonation of a nuclear weapon could have catastrophic consequences. A map module coordinates EP data associated with each selected channel and its associated position on the template model to provide this result, and can update the resulting map in the event that the channel or location is changed. Prior to transferring charges at a sensing section to a floating diffusion section, the charges remaining at the sensing section are removed from the sensing section by a potential barrier formed between the sensing section and a charge injection adjusting section.