LUMINANCE LEVEL CHANGING METHOD

PURPOSE:To correctly execute a level change by preparing a histogram based on the luminance level of each infrared detector for each frame and calculating true minimum and maximum luminance levels by accumulating generation frequencies in the histograms. CONSTITUTION:A histogram preparation part 11 prepares the histogram based on the luminance level obtained from the output of each infrared detector for each frame, and an accumulated picture element number calculation part 12 accumulates the number of generated picture elements in a direction from the minimum luminance to the maximum luminance of the histogram. Next, the number of generated picture elements is accumulated in a direction from the maximum luminance to the minimum luminance of the histogram, and a minimum/maximum luminance level decision part 13 defines the luminance level when being the number of accumulated picture elements more than a set value Nthr as the true minimum and maximum luminance levels respectively. By using these true minimum and maximum luminance levels, a level change part 14 changes the luminance level in the next frame to the level of a signal processing side. Thus, the minimum and maximum levels are stabilized and can be correctly changed.