changes in the degree of contour correction in accordance with luminance signal level differences in image processing are adjusted to be visually preferable . gamma correction is performed by a gamma correction circuit with respect to an intermediate image signal in which an edge signal is added to an original image signal . meanwhile , gamma correction is performed by a gamma correction circuit with respect to an intermediate image signal in which the edge signal is subtracted from the original image signal . these two intermediate image signals are subtracted from each other by a subtracter and the output thereof is added as an aperture signal to the original image signal that is output from a y signal gamma correction circuit .