1. An image generating apparatus comprising: a first input unit to which a predetermined parameter value about an image to be displayed is inputted; a second input unit to which a plurality of original images with respective parameters defined therefor are inputted; and an image generating unit for performing a predetermined converting process upon the plurality of original images in order to generate intermediate images from the plurality of original images such that the parameter values of the plurality of original images match each other, for combining the plurality of intermediate images thus generated such that their corresponding areas are made to overlap, and for outputting a final combined image; wherein said image generating unit performs a processing such that a parameter value of the final image matches the parameter value inputted with respect to said image to be displayed.