Image formation free from quality degradation is achieved by selecting whether to perform correction of color shift before or after a halftone process. When the amount of color shift is determined as larger than a predetermined threshold value, the halftone process is executed before a color shift correction process. On the other hand, when the amount of color shift is determined as equal to or smaller than the predetermined threshold value, the halftone process is executed after the color shift correction process. That is, with the large amount of color shift, the image degradation as a result of not being able to keep the number of screen lines when the correction of color shift is performed before the halftone process looks more conspicuous than the case with the correction of color shift after the halftone process.