Title :
Linearity of each channel pixel values from a surface in and out of shadows and its applications
Author :
Tian, Jiandong ; Tang, Yandong
Author_Institution :
State Key Lab. of Robot., Chinese Acad. of Sci., Shenyang, China
Abstract :
Shadows, the common phenomena in most outdoor scenes, are illuminated by diffuse skylight whereas shaded from direct sunlight. Generally shadows take place in sunny weather when the spectral power distributions (SPD) of sunlight, skylight, and daylight show strong regularity: they principally vary with sun angles. In this paper, we first deduce that the pixel values of a surface illuminated by skylight (in shadow region) and by daylight (in non-shadow region) have a linear relationship, and the linearity is independent of surface reflectance and holds in each color channel. We then use six simulated images that contain 1995 surfaces and two real captured images to test the linearity. The results validate the linearity. Based on the deduced linear relationship, we develop three shadow processing applications include intrinsic image deriving, shadow verification, and shadow removal. The results of the applications demonstrate that the linear relationship have practical values.
Keywords :
hidden feature removal; image colour analysis; realistic images; spectral analysis; SPD; channel pixel values; color channel; daylight; diffuse skylight; direct sunlight; intrinsic image deriving; linear relationship; outdoor scenes; real captured images; shadow processing applications; shadow removal; shadow verification; shadows; simulated images; spectral power distributions; sun angles; sunny weather; surface reflectance; Cameras; Image color analysis; Lighting; Linearity; Polynomials; Reflectivity; Sun;
Conference_Titel :
Computer Vision and Pattern Recognition (CVPR), 2011 IEEE Conference on
Conference_Location :
Providence, RI
Print_ISBN :
978-1-4577-0394-2
DOI :
10.1109/CVPR.2011.5995622