This article uses first by the Sobel operator determination picture edge approximate position

then uses three time transect interpolating function to carry on the interpolation computation to the gradation edge chart

enables the goal edge localization to achieve sub-pixel element level. Uses the threshold value iterative algorithm after the interpolation image to obtain the threshold value characteristic image again. The experiment indicated that this method can accurately locate object′s edge

to achieve sub-pixel accuracy

superior to the traditional edge detection methods.