In the process of crack identification for round logs, conventional edge extraction cannot effectively suppress noise because of the tree's annual ring lines and the similarity between the burr noises during cutting and the gray level of the target. Therefore, it is no easy to extract the target crack. The method of continuous gray-scale transformation enhancement is put forward in this thesis to increase the difference between the gray level of the background pixel and the gray level of the target so that can obtain an ideal pre-processed image. In the process of image preprocessing, the method of continuous gray-scale transformation enhancement is applied, that is to combine the gray-scale transformation enhancement and the non-linear filtering process so that can realize the preprocessing of the original image. The gray level difference between the extraction target and the background is increasing under the premise of preserving the image-extraction features. In the extraction process, the extracted target crack image is obtained through utilizing the localization minimum in mathematical morphology and then the compound morphological algorithm is designed based on the basic algorithm of mathematic morphology so as to obtain the target crack image which is connected by the edge curves. Results The MATLAB image processing algorithm is used to simulate each step of the method. The results show that the extracted target crack images are ideal. The mentioned algorit can not only ensure the integrity of the extraction target, but also can suppress the noise very well so that can satisfy the needs during the extraction of complex background images, especially the images with little difference between the background gray level and the extraction target gray level.
In order to improve the accuracy of phase extraction in 3D surface profile measurement of fringe reflection, combined with the phase-shifting technology and the calibration method of plane calibration target, the phase extraction and calibration experiments are carried out based on the establishment of a complete detection system and a non-linear camera model. For a plane mirror with a diameter of 100mm and a thickness of 25mm, first, according to the calibration method of the plane calibration target, the intrinsic and extrinsic parameters of camera are obtained; then, the images of the distortion stripes are obtained by the fringe reflection system, and they are corrected based on the camera calibration results; finally, the phase distribution before and after image correction is calculated by digital phase-shifting and phase unwrapping technique respectively. Experimental results show that the maximum phase extraction error is 0.1026 rad when only considering the second-order radial distortion coefficient: k1=-0.06068, k2=-0.09116.
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