1. An apparatus for converting an original set of source objects by reducing the number of objects required to display a description document, said apparatus comprising a generating means for generating a set of new objects, from said original set of source objects in the document, a number of new objects in said set of new objects being fewer than a number of objects in said original set of source objects, said fewer objects obtaining a display image equivalent to the display of an image obtained from said original set of source objects, wherein said generating means generates said new objects from a semi-transparent source object and other source objects located at a layer lower than a layer including said semi-transparent source object and spatially overlapping said semi-transparent source object, wherein said generating means generates a new merged object including at least a first source object having an area and a second source object having an area and superimposed on said first source object.