单幅航空影像中云阴影的自动去除

云阴影的存在严重影响了高分辨率航空遥感影像的视觉效果和影像质量.为去除云阴影,提出了一种无需人工参与的自动处理方法.首先采用光谱特征阈值法初步检测云阴影,再结合形态学方法进行后处理,提取完整的云阴影区域;阴影去除时,设计了一种利用非阴影区域信息、阴影整体区域信息、阴影像素局部窗口及像素本身信息的综合补偿模型,所需参数均可自动获取,进而实现阴影的自动去除.实验表明,区域级、窗口级和像素级多层次信息的引入,使模型的细节敏感度增强,提升了对比度,能灵活根据复杂的云阴影遮挡情况对阴影进行合理提升,有效解决了部分补偿方法存在的补偿效果不均匀的问题,阴影中地物的色彩与纹理等信息均得到更真实的再现.

Automatic Cloud Shadow Removal in Single Aerial Image

The existence of cloud shadow has a serious influence on the visual effect and image quality of aerial im-agery. In order to remove cloud shadow,an automatic method without any manual help was proposed. Firstly, according to the spectral characteristics of cloud shadow,the initial cloud shadow could be detected by spectral sig-nature with relative automatic threshold. Then the detection result would be post-processed by mathematical morphol-ogy to extract the complete cloud shadow area. Next,cloud shadow would be removed by a newly designed synthe-sized compensation model which utilizes the information of different areas including the whole shadow area and no-shadow area,a pixel-centered window area and the pixel itself. All the parameters in the model could be automati-cally acquired according to the information from aforementioned areas. Experimental results show that the use of dif-ferent information from whole area,window area and single pixel improves the ability of recognizing details and differences between pixels. In consequence,the contrast is promoted remarkably. Furthermore,the model is more flexible to deal with complex information shaded by cloud shadow,which resolves the problem existing in other methods that shadow areas are compensated unreasonably. The information of objects in shadow area including color and texture is restored more similarly to the truth.