1. An image forming system for printing an image including a plurality of objects, a part of the objects overlapping one another, the image forming system comprising: a computer that includes a print data generating circuit to generate print data of the image; and an image forming apparatus that includes a rendering circuit to execute rendering of the image based on the print data to print the image, wherein: the computer generates an object list indicating a list of the object that constitutes the image; the object list includes i) identification information of the object, ii) a “coordinate” indicating which position in the image the object is arranged, iii) an “attribution” of the object including a vector object, a raster object, and a text object, iv) a “transparency setting” indicating whether or not the object has transparency, v) an “overlapping target” indicating another object overlapping the object, and vi) an “overlapping condition” including a “partial”, a “fill”, and an “enclosed”, and indicating how the other object indicated in the “overlapping target” overlaps the object; the computer further includes an image generating circuit that generates an image object to indicate a state where the objects are overlapped in the image based on the “attribution”, the “transparency setting”, the “overlapping target”, and the “overlapping condition” included in the object list, with a reduced resolution at least partially compared with an actual resolution of the image; the print data generating circuit generates the print data including the at least one object included in the image, the image object generated by the image generating circuit, and overlapping information; and when processing the image object, the rendering circuit enhances the resolution of a part corresponding to the object in the image object based on a shape of the object indicated by the overlapping information, and wherein: if a specified image object of the print data indicates a state where a specified vector object is overlapping a specified raster object in the image, the specified image object is a raster object generated in a state where the resolution of a part that the specified vector object is overlapping the specified raster object is made lower than the actual resolution of the image, and the print data indicates that the specified image object overlaps the specified vector object; and the rendering circuit i) draws the specified vector object based on the print data, ii) draws the specified image object on the specified vector object based on the print data, and iii) performs a complementing process to the part corresponding to the specified vector object in the specified image object from a peripheral area based on the shape of the specified vector object indicated on which the specified image object overlaps by the overlapping information of the print data to enhance the resolution of the part.