A signal processing apparatus comprises an input unit for inputting first image data having a first resolution, a resolution converting unit for converting the resolution of the input first image data and outputting second image data having a second resolution which is lower than the first resolution, a character data producing unit for producing first character data in accordance with the second resolution, an enlargement unit for enlarging the first character data to produce second character data in accordance with the first resolution, a first multiplexing unit for multiplexing the input first image data and the second character data to produce first multiplex image data, and a second multiplexing unit for multiplexing the second image data output from the resolution converting unit and the first character data output from the character data producing unit to produce second multiplex image data.