依据点云强度校正的壁画纠正

摘要

Image rectification can reduce the distortion of digital mural image and attach rectified image with spatial properties, thus becomes one of key steps in mural image digital protection.As an intermediate data of 2D and 3D,intensity information of laser scanning is significant on texture mapping and rectification of mural images in grottos.However,the unusual phenomenon of laser intensity at near distance makes it very difficult on extracting feature points for image rectification needed.To el iminate the near distance effect on intensity-based mural rectification,the procedure of laser transmission was studied and the intensity function of defocusing effect of laser receiving optics was deduced.By dividing point cloud intensity values with corresponding values of functions with estimated parameters from col lected sample data,range and incidence angle invariant relative reflectance was generated,thus unusual intensity of point cloud data was corrected effectively.Experiments demonstrate that this method can effectively solve the problem of feature points in respect of low density and uneven distribution,thus achieve better results than general digital image processing method.%壁画纠正能消除数字壁画影像的变形并赋予其空间参数特性，是壁画数字化保护中的关键步骤之一。激光扫描数据作为壁画影像与三维空间的媒介，在壁画影像的纹理映射和纠正中具有重要的意义。然而，激光点云强度的近距离反常现象给壁画纠正中特征点的提取带来了困难。本文针对基于点云的壁画纠正中强度信息的近距离反常问题，研究了激光成像原理，推导了顾及激光接收系统散焦效应的强度函数，并采集样本数据进行模型参数估计，通过对估计模型和实际采集数据进行比较，生成不受距离和入射角影响的相对反射率，从而有效校正了强度异常的点云数据。试验表明，在壁画影像纠正过程中，该方法能有效解决强度影像提取特征点少且分布不均的问题，效果明显优于通用的数字图像处理方法。