平面壁画高分辨率图像的快速特征匹配方法

章昕烨 童卫青 李海晟

摘要：既有的图像特征匹配算法比较适合于一般分辨率的图像，且是在灰度图像上进行的.洞窟壁画图像的特点是分辨率非常高，并且还可能存在具有相同灰度纹理和不同颜色的区域.针对这类特殊图像，提出了一种面向高分辨率壁画图像的高速化特征匹配算法（简称NeoKPM算法）.NeoKPM算法有2个主要特点：①通过降采样图像获得原图像粗配准的单应变换矩阵，极大地降低了后续特征匹配的时间复杂度;②提出了一种基于灰度和颜色不变量的特征描述符，能很好地区分具有相同灰度纹理和不同颜色的特征点，提高了特征匹配的正确性.在实际壁画图像库上，对NeoKPM算法的性能进行了实验.实验结果表明，NeoKPM算法在分辨率为8 000万像素的壁画图像上，其每对图像的正确匹配点数量平均比SIFT（Scale Invariant Feature Transform）算法高出了近10万个;其特征点匹配平均处理速度是SIFT算法的20倍;其基于图像单个像素的双图像平均误差小于0.04像素.

关键词：壁画数字化;特征匹配;暴力匹配;颜色不变量

中图分类号：TP391文献标志码：ADOI：10.3969/j.issn.l000-5641.2021.06.008

A fast key points matching method for high resolution images of a planar mural

ZHANG Xinye1，TONG Weiqing1，2，LI Haisheng1

（1. School of Computer Science and Technology. East China Normal University，Shanghai 200062. China;

2. Shanghai Commercial Digital Printing Co.，Ltd. Shanghai 200041，China）

Abstract：Existing methods of key points matching were invented for grayscale images and are not suitable for high resolution images. Mural images typically have very high resolution，and there may be areas with the same gray textures and different colors. For this special kind of image，this paper proposes a high-speed algorithm of key points matching for high-resolution mural images （NeoKPM for short）. NeoKPM has two main innovations：（1）first，the homography matrix of rough registration for the original image is obtained by downsampling the image，which substantially reduces the time required for key points matching;（2）second，a feature descriptor based on gray and color invariants is proposed，which can distinguish different colors of texture with the same gray level，thereby improving the correctness of key points matching. In this paper，the performance of the NeoKPM algorithm is tested on a real mural image library. The experimental results show that on mural images with a resolution of 80 million pixels，the number of correct matching points per pair of images is nearly 100 000 points higher than that of the SIFT （Scale Invariant Feature Transform）algorithm，the processing speed of key points matching is more than 20 times faster than that of the SIFT algorithm，and the average error of dual images based on a single pixel of theimage is less than 0.04 pixels.

Keywords：mural digitizing;key points matching;brute force matching;color invariance

0引言

洞窟壁畫是人类的艺术瑰宝，数字化保存是其重要的保护方法.根据我国国家文物局关于古壁画的一级影像采样分辨率不低于300 DPI（Dots Per Inch，每英寸点数）的技术要求[1]，目前任何高分辨率的相机都无法通过拍摄一幅图像来保存大幅面的洞窟壁画.因此，一般采用划分壁画采集区块的方法，即把一幅大幅面的壁画划分成n×m大小的有重叠的采集区块，然……