1. An image processing apparatus comprising: an obtaining unit configured to obtain image data; an input unit configured to input a parameter related to a deformation process for the obtained image data; a processing unit configured to generate image data for projection by performing the deformation process to the obtained image data based on the parameter input by the input unit; and a control unit configured to determine whether an angle between the obtained image data and the image data for projection is out of a predetermined range and to control said processing unit not to perform the deformation process if said control unit determines that the angle between the obtained image data and the image data for projection is out of the predetermined range.