Sub-pixel technique in ring light method

Aiming at the deep hole detection, the method of ring light section is introduced and its principle is analyzed. To enhance its detection precision and eliminate the influence of error and noise on its detection result, such as the error caused by CCD quantization and saturation, the unevenness and speckle of the laser light and so on, a sub-pixel detection technique is proposed. This technique layouts a series of transversal lines on the ring light spot image, reconstructs their continuous gray distributions, estimates their ideal gray distributions based on wavelet transform, and computes their ideal extreme gray points. By these extreme gray points, the ideal extreme gray line of ring light spot is detected in sub-pixels and then the profiles of deep hole are measured. With a property of high precision (0.1 pixels), high power of noise proof, no data deficit and data redundancy, and a capability of complicated profile line detection, this technique is important for measuring complicated inner surface of deep hole.