An image processing apparatus for simulating a print output of a printing machine. The image processing apparatus firstly acquires color value information for converting color value information of image data so that a color reproduced on one surface of a recording medium by the printing machine based on the color value information is reproduced as an output. The image processing apparatus secondly acquires show-through color profile information for converting the color value information so that the color reproduced on the one surface by the printing machine as seen from the other surface is reproduced. The image processing apparatus then generates image data formed by composing first image data obtained by converting the color value information based on the color profile information, with second image data obtained by converting the color value information based on the show-through color profile information and by inverting the converted color value information horizontally or vertically.