An image processing apparatus handling combined data including read data from a scanner and written data written by a touch pen, capable of performing appropriate color conversion both on the read data and written data is provided. When a display image obtained by combining the read data and the written data is to be printed, the image processing apparatus executes first image processing on the read data, and second image processing on the written data, respectively. By an image forming apparatus, the combined data including the read data and the written data, which have been appropriately color-converted by respective image processing, is printed.