Abstract:

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 eliminate 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 collected 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.

Key words: laser scanning point cloud, intensity correction, defocusing effect, mural image rectification