1. An image processing apparatus, comprising: a document reading unit configured to read a plurality of image data each having a different phase from a document by single scanning; a super-resolution processing unit configured to generate super-resolution image data by using the plurality of image data each having a different phase, so as to have super-resolution higher than those of the plurality of image data; and an image processing unit configured to carry out multiple image processing to the super-resolution image data, wherein each of the multiple image processing is associated with specific resolution; and wherein the super-resolution processing unit starts super-resolution processing at the time when image data necessary for obtaining the specific resolution associated with any of the image processing is obtained.