1. An image processing method comprising: subjecting captured-image data outputted from an image-capturing device to an optimization processing for appreciation to produce viewing image referred image data; and conducting a pre-processing before the optimization processing is carried out; wherein, the pre-processing comprises to transform the frequency characteristic of the captured-image data into the scene-referred frequency characteristic by removing the effect of a frequency characteristic specific to the image-capturing device from the frequency characteristic of the captured-image data.