1. A signal processing apparatus comprising: an input unit which inputs moving image information; a designation unit which designates a plurality of objects in the moving image information; a detection unit which detects a position of each of the plurality of objects, designated by the designation unit, the moving image information; an enlargement unit which generates a plurality of enlarged images by enlarging an image including a part of each of the plurality of objects designated by the designation unit; a superimposition unit which superimposes the plurality of enlarged images on the moving image information; an output unit which outputs the moving image information obtained by the superimposition unit to a display apparatus; and a controller which controls the superimposition unit so as to decide a superimposition position of each of the enlarged images in accordance with the positions detected by the detection unit, wherein, if the positions, detected by the detection unit, of the plurality of designated objects in the moving image information are in a predetermined relation to each other, the enlargement unit generates one enlarged image by enlarging an image simultaneously including parts of the plurality of objects having the predetermined relation in place of the plurality of enlarged images obtained by enlarging the parts of the plurality of the objects under the predetermined relation.