This invention has as its object to efficiently encode an image. To this end, for example, an image undergoes a color reduction process using a dither matrix with a predetermined size. A print control command is output. A compression parameter designation command that designates an up copy vertical offset value (a value according to the matrix size), a near left copy horizontal offset value (a value according to the matrix size), and a far left copy horizontal offset value (a value according to the period of background patterns), which are used in encoding, is output. Image data is encoded according to an encoding sequence.