1. A projector for displaying an image on a projection surface comprising: a light source configured to emit light; an image formation panel configured to form an effective panel image for modulating light emitted by the light source into effective image light representing an image, the image formation panel being formed in an image formation area of a panel surface; and an image processor including a zoom adjusting module and a keystone correcting module, the image processor configured to correct for trapezoidal distortion on the projection surface by (1) adjusting the zoom level of a zoom lens to a target zoom level, and (2) performing a keystone correction; the image processor correcting for trapezoidal distortion of the image displayed on the projection surface by means of forming the effective panel image in a revised image formation area, the revised image formation area being part of the image formation area of the panel surface; the zoom adjusting module adjusting the zoom level to the target zoom level; the target zoom level being a zoom level in which a total projection area encompasses the projection surface, and in which a perimeter of the total projection area contacts the perimeter of the projection surface at one or more contact points, the total projection area being an area onto which is projected image light corresponding to all areas of the image formation area of the panel surface; and the keystone correcting module performing a keystone correction such that the perimeter of the revised image formation area contacts the perimeter of the image formation area of the panel surface, the contact between the revised image formation area and the perimeter of the image formation area of the panel surface being at a point on the perimeter of the image formation area of the panel surface corresponding to the contact point of the perimeter of the total projection area with the perimeter of the projection surface.