Abstract: A kind of image processing method is introduced, which is based on the classical method about edge detection. Gray restrain is brought in，and the relations between the grid and its eight neighbours are considered in calculating the gradient. There are several optics which are laid with Browster angle and the image collected by CCD includes many noises, so the components of the image are quite complex and the quality is bad. The advanced method has been proved that it is possible to get over the problem and get information about the size of damage accurately. In addition, systemic analysis and calculation of optic damages are presented. The result shows that the damage size calculated in advance accords with the real size, and the error is in the scope of permission. The image processing m