Method for correcting luminance gradation in an image pickup apparatus

Abstract

A synthesized picture signal of a dynamic image is produced by combining a long-time picture signal representing a low luminance and a short-time picture signal representing a high luminance, pieces of histogram data corresponding to a plurality of luminance levels are detected from the synthesized picture signal, a sum of values of pieces of histogram data is repeatedly calculated as a summed value of a piece of summed histogram data while the number of pieces of histogram data is increased, and an inclination of a line indicated by a series of summed values is detected as a luminance gradation characteristic. Thereafter, the luminance gradation characteristic is corrected to a corrected luminance gradation characteristic according to a relationship between a maximum luminance level and an upper limit luminance level of a dynamic range, and a luminance gradation corrected signal composed of the pieces of histogram data corresponding to gradation corrected luminance levels is produced according to the corrected luminance gradation characteristic to make a maximum gradation corrected luminance level equal to or lower than the upper limit luminance level. Therefore, a low luminance object and/or a high luminance object can be clearly reproduced within the dynamic range.