Spherical harmonics vs. Haar wavelets: basis for recovering illumination from cast shadows
Spherical harmonics vs. Haar wavelets: basis for recovering illumination from cast shadows
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DOI：
10.1109/cvpr.2004.239
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发表时间：
2004-07
期刊：
影响因子：
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通讯作者：
Takahiro Okabe;Imari Sato;Yoichi Sato
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文献类型：
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作者：
Takahiro Okabe;Imari Sato;Yoichi Sato
从图像估计照明分布的问题称为逆照明。对于逆向照明，基于镜面反射分量、漫反射分量和投射阴影开发了三种方法。本研究提供了关于为什么基于投射阴影的方法能够以可靠的方式工作的理论见解，并讨论了哪种基函数适合用于从投射阴影中恢复照明。首先，我们使用球谐函数形式化基于投射阴影的方法。然后，我们在频域中分析该方法并展示该方法的优点和局限性。其次，受频域观察的启发，我们提出了一种使用 Haar 小波的有效方法，该方法提供紧凑的支持和系数的稀疏性。最后，我们报告了比较使用球谐函数的方法和使用 Haar 小波的方法的实验结果。
The problem of estimating an illumination distribution from images is called inverse lighting. For inverse lighting, three approaches have been developed based on specular reflection components, diffuse reflection components, and cast shadows. The present study provides theoretical insights as to why the approach based on cast shadows works in a reliable manner, and discusses what kind of basis functions are appropriate to be used for recovering illumination from cast shadows. First, we formalize the approach based on cast shadows by using spherical harmonics. Then, we analyze the approach in the frequency domain and show the advantages and the limitations of the approach. Second, motivated by the observations in the frequency domain, we propose an efficient method using Haar wavelets that provide compact supports and sparsity of coefficients. Finally, we report the results of experiments that compared the method using spherical harmonics and the method using Haar wavelets.