A novel shadow detection and restoration algorithm based on atmospheric phenomena

Due to the degradation of an aerial image due to occluding of sunlight, namely shadows, algorithms like segmentation and object recognition may be highly influenced negatively. This paper describes a novel shadow restoration algorithm based on atmospheric effects and characteristics of sun-light for aerial images. In this work, first shadow regions are detected exploiting the Rayleigh scattering phenomena and the fact that shadows have low illumination intensity. After detection shadow restoration is achieved by first restoring partially occluded shadow areas, with modeling these transition regions with a sigmoid function. Then, fully occluded shadow regions are restored by first segmenting the image to uniformly illuminated regions, then multiplying the intensity in these regions with a constant, which is determined by the ratio of intensities between each segment and its non-shadow neighborhood. The experimental results yield better results when compared with the other methods in the literature.