A method of processing image data according to an embodiment of the present invention includes: setting a permissible pitch range for a distance between adjacent ink blots; arranging image data for the line pattern in an x-y coordinate system; selecting a first base point corresponding to one side of the image data for the line pattern; selecting a first determination point from the first base point, in which the first determination point is parallel to and separated from one side of the image data for the line pattern; determining whether a distance between the first base point and the first determination point is within the permissible pitch range; and storing a coordinate as print data if the distance between the first base point and the first determination point is within the permissible pitch range, in which the coordinate is located at a shortest distance from the first determination point.