Parallax Image Alignment With Two-stage Mesh Optimization Based on Homography Diffusion Constraints
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摘要: 目前, 在带有视差场景的图像对齐中, 主要难点在某些无法找到足够匹配特征的区域, 这些区域称为匹配特征缺失区域. 现有算法往往忽略匹配特征缺失区域的对齐建模, 而只将有足够匹配特征区域中的部分单应变换系数(如相似性变换系数)传递给匹配特征缺失区域, 或者采用将匹配特征缺失区域转化为有足够匹配特征区域的间接方式, 因此对齐效果仍不理想. 在客观事实上, 位于相同平面的区域应该拥有相同的完整单应变换而非部分变换参数. 由此出发, 利用单应变换系数扩散的思想设计了一个二步网格优化的图像对齐算法, 简称单应扩散变换(Homography diffusion warping, HDW)算法. 该方法在第一步网格优化时获得有足够匹配特征区域的单应变换, 再基于提出的单应性扩散约束将这些单应变换系数扩散到邻域网格, 进行第二步网格优化, 在保证优化任务简洁高效的前提下实现单应变换系数的传播与图像对齐. 相较于现有的针对视差场景图像对齐算法, 所提方法在各项指标上都获得了更好的效果.Abstract: At present, the main difficulty in the image alignment with parallax scene is in the areas that cannot find sufficient matching features. We call these areas featureless regions. Cutting-edge research on parallax image alignment neglects modeling of regions without matching features. Indirect methods such as transferring partial homography of regions with matching features to featureless regions or transforming featureless regions to regions with matching features have been popularly used, which, however, do not guarantee satisfactory results. In fact, image regions belonging to the same plane should possess the same homography. In this paper, a two-stage mesh optimization algorithm, homography diffusion warping (HDW), is designed by homography diffusion. In the first stage, homography coefficients of mesh cells in the image regions with matching features are obtained. Then we propagate these homography coefficients to adjacent cells to form homography diffusion constraints, and perform the second stage optimization of the mesh by enforcing the constraints on the premise of ensuring the simplicity and efficiency of the optimization task. Compared with existing image alignment algorithms, the method proposed in this paper achieves better results on all metrics.
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Key words:
- Image alignment /
- parallax scene /
- mesh optimization /
- featureless regions
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表 1 HDW相对其他算法在Err、PSNR和SSIM上的平均改进(%)
Table 1 The average improvement of HDW compared with other algorithms on Err, PSNR, and SSIM (%)
表 2 图像对的对齐效果量化指标对比
Table 2 Quantitative comparison of alignment performance on image pairs
Plant Carpark Stationery SMH[17] Err 1.2338 1.2659 1.0580 PSNR 15.7496 12.3758 22.9365 SSIM 0.6516 0.5719 0.9316 PCPS[18] Err 0.9396 1.1923 0.6695 PSNR 15.3314 11.5550 23.5924 SSIM 0.6858 0.5687 0.9355 APAP[6] Err 4.1854 1.1337 1.0154 PSNR 13.2995 11.9361 23.4257 SSIM 0.6245 0.6354 0.9236 CPW[8] Err 6.3718 1.6435 0.9038 PSNR 12.7397 11.2034 23.4680 SSIM 0.4818 0.5862 0.9258 ACW[41] Err 3.4302 0.7918 0.8070 PSNR 13.2159 12.0738 23.6319 SSIM 0.6589 0.6505 0.9278 HDW Err 0.2741 0.2787 0.5134 PSNR 18.1968 13.5019 24.2972 SSIM 0.8221 0.7143 0.9400 -
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