A terminal device usable in connection with an external display device is disclosed, which receives a plurality of sub-image data sets into which an original image data set has been divided, with each sub-image data set having a size within a display area size of the terminal device; converts an image format of the plurality of sub-image data sets into the same image-format as an image format of the external display device, on a per-sub-image-data-set basis; regenerates the original image data set from the plurality of format-converted sub-image data sets, such that the original image data set is formed in its entirety or in plural data blocks; and outputs the regenerated original-image-data-set to the external display device.