PURPOSE: To provide picture quality having more natural resolution feeling by satisfactorily balancing the size of an aperture signal and that, of a luminance signal corresponding to a photographic scene, improving the reproducibility of a high luminance signal by fluctuating a knee point, and applying the suitable aperture signal interlocked with the fluctuation of the knee point.

CONSTITUTION: When an image is made brighter than standard brightness, the reproducibility of the high luminance signal is improved by lowering the knee point of an automatic knee circuit 32. While being interlocked with the fluctuation of the knee point, the gain of the aperture signal generated based on the input side image signal of the automatic knee circuit is fluctuated, and this gain adjusted aperture signal is added to the output side of a gamma correction circuit 34. Therefore, since the high luminance signal is more compressed when the knee point is low, the gain of the aperture signal is lowered so as to prevent aperture from being unnaturally over applied.