Abstract: An automatic gain control apparatus wherein red, blue and green channels of an input image signal are supplied directly, and indirectly through variable gain amplifiers, to black-level non-additive mixing circuits, respectively, and the channel signals of the input image signal are further supplied to a white peak non-additive mixing circuit for selecting a maximum level of the input image signals. Each of the gains of the variable gain amplifiers is controlled based on the selected maximum level for varying the knee slope in a manner such that the output image signal obtained from the black-level non-additive mixing circuits takes a white clip level at the peak level of the input image signal. Since any collapse of peak portions in the white level of the input image signal can be prevented regardless of a wide variation in a dynamic range of the input image signal.