A driver program is provided for causing a host apparatus to execute a processing of generating color-converted image data and transferring it to a printing apparatus, this program making it possible to decrease the volume of image data to be stored in the host apparatus and to conduct data transfer without delaying the printing completion. A driver program causes a host apparatus to execute a processing of generating image data comprising data of a plurality of colors and transferring it to a printing apparatus. When the transfer of the image data of one plane is conducted, the driver program causes the host apparatus to execute a transfer processing conducted by intermingling a step of transferring by each band of the bands obtained by dividing the image data of one plane at the prescribed height, and a step of transferring by each color of the plurality of colors.