A control apparatus for controlling an image forming system is provided. The image forming system includes transparent toner image forming device configured to form a transparent toner image on a sheet on which a color toner image has been fixed and includes fixing device configured to fix the transparent toner image formed on the sheet. The control apparatus includes an obtaining means for obtaining information of a first part of a color toner image area on which transparent toner is to be applied with a first amount per unit area after the color toner image is fixed, and a control means for controlling the transparent toner image forming device to apply the transparent toner, with a second amount per unit area, on a second part of the color toner image area which is the color toner image area excluding the first part, after the color toner image is fixed. The second amount is smaller than the first amount.