Naturalness of warping is gaining extensive attention in image stitching. Recent warps such as SPHP, AANAP and GSP, use a global similarity to effectively mitigate projective distortion (which enlarges regions), however, they necessarily bring in perspective distortion (which generates inconsistency). In this paper, we propose a quasi-homography warp, which balances perspective distortion against projective distortion in the non-overlapping region, to create natural-looking mosaics. Our approach formulates the warp as a solution of a system of bivariate equations, where perspective distortion and projective distortion are characterized as slope preservation and scale linearization respectively. Our proposed warp only relies on a global homography thus is totally parameter-free. A comprehensive experiment shows that quasi-homography outperforms some state-of-the-art warps in urban scenes, including homography, AutoStitch and SPHP. A user study demonstrates that quasi-homography wins most users' favor as well, comparing to homography and SPHP.

本文提出了一种新型准同（quasi-homography）变形方案，通过全局相似性变形有效平衡了透视畸变和投影畸变。对于非重叠区域，该方案使全景图更自然展现。实验结果表明，相比于同源性（homography）、自动拼接（AutoStitch）和SPHP等算法，准同变形在城市场景中表现更优，并且在用户调查中获得了大多数用户的青睐。

图像拼接中的准同态变换