A large undivided image may be displayed by combining primary images displayed by two or more display units. Due to inactive edge regions of the display units, there is a gap between the primary images. To eliminate the gap, the paths of light rays transmitted from the display units are shifted and/or bent to form secondary images based on said primary images. Paths of light rays transmitted from a single display unit are shifted and/or bent substantially in only one direction. Consequently, the secondary images are shifted with respect to said primary images such that a gap between said secondary images is substantially eliminated. Advantageously, the secondary images are formed using an element comprising a plurality of linear and parallel prisms which have equal prism angles.