An image processing apparatus comprises: an unit configured to extract first color data and first attribute data from a pixel value, and to extract second to fourth color data and second to fourth attribute data corresponding to a second pixel value to a fourth pixel value corresponding to the arrangement pattern defined in a specified pattern flag; an unit configured to hold the pattern flag, the first color data, the second to fourth color data, the first attribute data, and the second to fourth attribute data; an unit configured to determine whether attribute data of all pixels included in a tile are identical; and an unit configured to perform control to delete the first attribute data and the second to fourth attribute data, and to store, in header information, information indicating that the attribute data in the tile are identical and information of the attribute data determined to be identical.