| Description: The minimum allowable exposure time from an MDIS automatic exposure time calculation. In a test image that it analyzed to determine an exposure time using automatic exposure, DPU hardware generates a histogram of the image. The histogram is analyzed by the software to determine if the image is overexposed or underexposed, and the exposure time is adjusted accordingly by analyzing the histogram of raw DN values in different brightness bins. The background or dark current level (mess.mdis.aex_bacb) is taken into account an is assumed to be a constant value. A threshold of number of pixels (mess.mdis.aex_sthr) is allowed to exceed a target brightness (mess.mdis.aex_tgtb). Starting with the maximum value, the number of pixels exceeding the target is counted, and the brightness of the histogram bin in which that threshold is reached (mess.mdis.aex_stat) is reported. The exposure time is scaled back by the ratio of mess.mdis.aex_tgtb/mess.mdis.aex_stat. |