Laser Stripe Center Detection Under the Condition of Uneven Scattering Metal Surface for Geometric Measurement

The uneven reflective metal surface has great influence on the high-precision measurement of the structured light 3-D shape. By analyzing the laser scattering and reflection models, a set of light stripe center’s subpixel extraction methods which has strong robustness is proposed. The method first cuts off the influence of the uneven fixed background by using the difference image method to process the bright field and the dark field. Then, the regional growth statistics method is used to eliminate the influence of random laser speckle noise, and then the gray-gravity method is used to obtain the coarse center of the laser stripe. The Sobel operator is used to obtain the gradient vector of the stripe pixel point, and then the normal direction field of the light stripe is obtained. The normal direction field vector is taken as the direction to find the $5\times5$ neighborhood of the coarse light stripe’s center, and then the gray-gravity method is reused to determine the center position of the laser stripe in the normal line direction; the pixel coordinates of the subpixel level are obtained by using bilinear interpolation. The experimental results show that the method can effectively eliminate the interference of flash point noise and has strong robustness. The detection error of the stripe is less than 0.1 pixels, which ensures the system measurement accuracy. Compared with other methods, the system’s resolution can reach 0.02 mm.