Currently

the resolution of industrial-grade array CCD sensor can hardly satisfy the high precision requirements on the edge detection across a huge field.For the system of steel plate dimensional measurement

this paper introduces running environment and operation principle.Then

it proposes a sub-pixel level edge detection algorithm for steel plate dimensional measurement based on Zernike moment and also its theory applied to sub-pixel detection.This algorithm has good anti-noise performance and high detection precision.Moreover the proposed algorithm also improves the traditional threshold method for processing edge points

which can obtain an edge within a single pixel width and the location in sub-pixel level.In practice

the results show that the proposed algorithm improves the measurement accuracy and has efficient effect as well as practical value.