US Patent 7686457 Projection image display apparatus and multi-projection system

A projection image display apparatus is disclosed which enable users to observe an image in an overlap area well. The apparatus comprises a first projector which projects a first image onto a projection surface, a projection area detector which acquires a projection area onto which a second projector projects a second image in a certain area of the projection surface. Further, the apparatus comprises a projection area controller which controls a projection area onto which the firs projector projects the first image, based on an input signal from the projection area detector.