1. A method of exchanging between devices information related to a look-up table that is referenced in order to obtain a post-adjustment processing image data value corresponding to pre-adjustment processing image data value, comprising: exchanging at least a plurality of control points between an image input apparatus and an information processing apparatus, which is an external device of the image input apparatus, the control points, in combination with an interpolation operation, specifying a characteristics curve that defines conversion characteristics of a look-up table; the exchanging comprising, outputting the control points from the image input apparatus to the information processing apparatus, receiving adjustments of the control points in the information processing apparatus from a user and generating the look-up table, based on the adjusted control points, and outputting the adjusted control points and the generated look-up table from the information processing apparatus to the image input apparatus; and converting the pre-adjustment processing image data value to the post-adjustment processing image data value with reference to the look-up table received by the image input apparatus.