Image transmission apparatus and control method therefor, and image display system

摘要

An image of an area smaller than the number of horizontal pixels and the number of vertical pixels of an external image display apparatus is extracted from a display area if the number of horizontal pixels of a part of a display area designated by a designation unit is greater than the number of horizontal pixels of the external image display apparatus acquired by an acquisition unit and/or if the number of vertical pixels of the part of the display area designated by the designation unit is greater than the number of vertical pixels of the external image display apparatus acquired by the acquisition unit.