Projection-type display apparatus and geometric distortion correcting method for correcting geometric distortion

A geometric distortion correcting method comprising the steps of:

• obtaining, with a processor, information relating to a first effective area, which is the largest usable area for a display of a display unit, information relating to a second effective area, which is set in and smaller than the first effective area and is a virtual effective area whose geometric distortion has not yet been corrected, and information used to correct a geometric distortion;
• and
• correcting, with the processor based on the information obtained by the obtaining step, a geometric distortion by performing, for an input image that is superimposed onto an image of the second effective area, enlargement processing so that a third effective area, which is a post-correction virtual effective area, has a portion located in an area between the first effective area and the second effective area and the second effective area, which is the post-correction virtual effective area, is enlarged, if the third effective area is entirely contained in the first effective area, and by further performing reduction processing, if the third effective area has a portion that is located outside the first effective area, to reduce the third effective area so that the third effective area is entirely contained in the first effective area.