Edge extraction is necessary and plays an important role in visual quality control in manufacturing process.Aiming at rapid and high-accuracy edge location for on-line examination,a kind of sub-pixel edge location technique based on lookup table is studied.Firstly,it is proved that the abscissa of the point corresponding to one-order derivative maximum of continuous image edge spread function is a precise edge location point.Then,the relation between real edge location error and gray gap is deducted by simulation.According to the simulation result,sub-pixel edge location can be realized by calculating maximum point of one-order differential of continuous edge spread function.Finally,X-ray imaging experiments are designed to establish the general model of edge location and error analysis of edge location is also provided.