An image processing apparatus is provided in which, even if a nonlinear characteristic of a luminance-type gamma correction circuit for converting a luminance signal is changed, saturation with respect to a luminance output can be nearly constant. A signal amount of the luminance signal generated from image data that exceeds a previously defined threshold is calculated. A first nonlinear characteristic is selected from a plurality of nonlinear characteristics previously set depending on the calculated signal amount. Nonlinear conversation is performed on a signal generated from the image data to determine luminance with the selected first nonlinear characteristic. An output ratio of the first nonlinear characteristic to a second nonlinear characteristic is prepared and the second nonlinear characteristic is defined so that the output ratio is satisfied. Nonlinear conversion is performed on a signal that has been generated from the image data to determine saturation with the selected second nonlinear characteristic.