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首页> 外文会议>Media forensics and security >Lighting analysis of diffusely illuminated tableaus in realist paintings: An application to detecting 'compositing' in the portraits of Garth Herrick
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Lighting analysis of diffusely illuminated tableaus in realist paintings: An application to detecting 'compositing' in the portraits of Garth Herrick

机译：写实绘画中的漫反射场景的照明分析：用于检测Garth Herrick肖像中“合成”的应用

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The problem of estimating the direction of point-source illumination in digital photographs has been studied extensively, and the cast-shadow and occluding-contour algorithms have been used to detect tampering and compositing; differences between the lighting directions estimated from different objects indicate that at least one of them was composited into the image. Such methods have also been applied to the analysis of realist paintings to estimate the position of illuminants within a tableau and thereby test for artists' use of optical aids. Recently, the occluding-contour algorithm has been enhanced to address the case of diffuse illumination, for instance from light passing through several windows, from multiple lamps, and so forth. Here, the pattern of lightness along the occluding contour of an object is expressed as a weighted sum of spherical harmonics. Significant differences between the coefficients extracted from different objects indicates that they were recorded under different illumination conditions, and thus that one or more was likely composited into the image. We apply this technique to the analysis of diffuse lighting in realist paintings, focussing on the portraits of the contemporary American realist Garth Herrick. Herrick often works with multiple photographs as referents, for instance a photograph of the portrait subject and a different photograph of the background. There is no guarantee that the two lighting conditions are the same, nor that Herrick can perceive or compensate for such lighting discrepancies when executing his painting. We tested for lighting consistency throughout two of his paintings: one based on a single photographic referent, and another "composited," i.e., based on two photographic referents. Our algorithms found great illumination consistency in the first painting and significant inconsistencies in the second painting-inconsistencies difficult to discern by eye. As such, our methods reveal this artist's working methods. Our algorithms have broad applicability to the study of studio practice throughout the history of art.
机译：数码照片中估计点源照明方向的问题已被广泛研究，并且使用投射阴影和遮挡轮廓算法来检测篡改和合成。从不同对象估计的照明方向之间的差异表明，至少有一个被合成到了图像中。此类方法也已应用于现实主义绘画的分析，以估计光源在画面中的位置，从而测试艺术家使用光学辅助工具的情况。最近，增强了遮挡轮廓算法，以解决漫射照明的情况，例如，来自穿过多个窗口的光线，来自多个灯的光线等等。在此，沿着物体的遮挡轮廓的亮度模式被表示为球谐函数的加权和。从不同物体提取的系数之间的显着差异表明它们是在不同的照明条件下记录的，因此一个或多个可能会合成到图像中。我们将这种技术应用于现实主义绘画中的漫射照明分析，重点是当代美国现实主义画家Garth Herrick的肖像。 Herrick经常将多张照片作为对象，例如肖像对象的照片和背景的其他照片。不能保证两个照明条件都相同，也不能保证Herrick在执行绘画时可以感知或补偿这种照明差异。我们测试了他的两幅画的照明一致性：一幅是基于一个摄影对象，另一幅是“合成的”，即基于两个摄影对象。我们的算法发现在第一次绘画中存在很大的照明一致性，而在第二次绘画中存在显着的不一致，这是肉眼很难辨认的。因此，我们的方法揭示了这位艺术家的工作方法。我们的算法在整个艺术史上对工作室实践的研究具有广泛的适用性。

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