1. An image processing apparatus for inputting image data of a photographed image containing a plurality of pixels and for converting the image data of each of the pixels, the apparatus comprising: a first holding unit which holds a plurality of correspondence relationship information for a conversion of the image data; a second holding unit which holds relationship information related to an applicable object of an image processing, correlating it to process content information representing details of the image processing; an applicable object judgment unit which judges, with reference to the relationship information, whether a pixel corresponding to the input image data is the applicable object of the image processing; a correspondence relationship specification unit which, in a case where it is judged that the pixel is the applicable object of the image processing, with reference to the process content information correlated to the referenced relationship information, specifies the correspondence relationship which actualizes the contents of the image processing from among the plurality of correspondence relationships; and an image data converting unit which, in the image data of a pixel on which the specification of the correspondence relationship is performed, makes the conversion on the image data of the pixel, with reference to the specified correspondence relationship, and in the image data pixels in a transition region between regions being different in terms of correspondence relationship, makes the conversion on the image data of the pixel in such a way that a level of correspondence relationship is gradually adjusted in image data conversion.