Raw image data obtained by shooting is thinned at a thinning rate, which is determined in accordance with a shooting scene, to produce simple raw image data. The thinning rate is determined such that necessary information for proper checking is maintained and unnecessary information for checking is thinned. Image correction is performed for the simple raw image data with predetermined processing parameters, and this data is converted into a simple display image to be shown on a monitor. An operator observes the simple display image to change the processing parameters. Whenever the processing parameters are changed, the image correction is performed for the simple raw image data with the changed processing parameters to update the simple display image. For the raw image data, image correction is performed with the finally determined processing parameters.