and the ceiling value it may be noticed that each of these statistical methods if used alone may not produce the best statistical results and therefore the best image exposure for instance with the peak value method a very focused bright spot in a region may force a few pixels to reach the preset saturation ceiling very quickly while the rest of the pixels in the region are underexposed or not be exposed at all however if an average luminance value for the region was also calculated it may become obvious that a bright spot exists and an adjustment in the exposure time made to compensate an ordinary person skilled in this art may be able to determine the best combination of statistical methods to obtain the most reliable statistical method fig6 illustrates the idea of time interval sampling in the present invention fig6 is a graphical illustration of the exposure status of an exemplary photodetector the monitoring unit 112 may be preset to sample the photodetector every 100 ms from the beginning of the exposure period the luminance value after 100 ms have elapsed from the beginning of the exposure period is illustrated by 602 and after 200 ms is illustrated by 604 at 400 ms the photodetector is close to the.