1. An image processing apparatus comprising: an input unit configured to input image data; a first determination unit configured to determine whether a pixel included in the input image data belongs to an edge; a second determination unit configured to determine whether a pixel included in the input image data is achromatic; and a processing unit configured to perform a process for forming a pixel only with an achromatic color material on a pixel determined as belonging to an edge and being achromatic by the first and the second determination units, wherein, in a case where the pixel has been determined as belonging to an edge and being achromatic, the processing unit determines whether the process is to be performed on a pixel adjacent to the pixel which has been determined as belonging to an edge and being achromatic, and, in a case where it has been determined that the process is to be performed, performs the process on the adjacent pixel.