基于分区域自适应阈值Zernike矩的骨签轮廓尺寸测量方法

Bone Stick Contour Dimension Measurement Based on Sub-Regional Adaptive Threshold Zernike Moments

汉长安城遗址出土骨签数量庞大,基于数字图像技术的骨签尺寸自动测量方法能够提高工作效率。针对骨签纹理繁多、边缘对比度低导致测量精度不高的问题,提出一种基于分区域自适应阈值Zernike矩的骨签图像尺寸测量方法。首先,利用Canny算子进行像素级定位;然后,对称设定边缘有效分区域,以欧氏距离为比例系数计算各个分区域像素点与中心点的加权灰度值,作为各区域Zernike矩提取边缘的判定阈值,提取骨签亚像素级边缘;其次,引入边缘轮廓判别条件剔除无效纹理,获取骨签图像精确轮廓;最后,使用最小外接矩算法计算骨签不规则轮廓,结合相机标定完成骨签尺寸测量。实验结果表明,与其他方法相比,该方法测量的骨签长宽的均方根误差分别降低1.3 mm和1.2 mm,平均相对误差分别降低3%和6.3%,平均绝对误差分别降低1.23 mm和1.08 mm,能够有效提高复杂边缘轮廓的骨签尺寸测量精度。

A huge number of bone swabs are unearthed from the Chang’an city site of the Han dynasty,and the automatic measurement method of bone swab size based on digital image technology can improve the work efficiency at such sites.An approach for measuring the size of a bone swab image based on an adaptive threshold Zernike moment in various places is proposed to address the issue of low measurement accuracy brought on by variable bone swab textures and low edge contrast.First,the Canny operator is used for pixel-level localization.Then,the effective edge of each sub-region is fixed symmetrically;the weighted gray value of each sub-region pixel point and center point is calculated with Euclidean distance as the proportion coefficient;and the judgment threshold of the Zernike moment extraction edge of each region is used to extract the subpixel edge of the bone swab.Finally,to remove the invalid texture,the edge contour discrimination condition is added,and the precise contour of the bone swab picture is obtained;the size of the bone swab is estimated using camera calibration,and the irregular contour is obtained using the minimum circumscribed rectangle algorithm.The experimental results demonstrate that the root mean square error of the length and width of the bone swab measured by this method decreases by 1.3 mm and 1.2 mm,the average relative error decreases by 3%and 6.3%,and the average absolute error decreases by 1.23 mm and 1.08 mm,respectively,compared with other methods.Thus,the method can effectively enhance the measurement accuracy of the size of the bone swab with complex edge profiles.