监控系统中，观测视场被遮挡，会导致显示的图像中存在遮挡阴影，影响对图像的进一步分析和处理。针对该问题，提出了一种实时检测遮挡阴影的算法。该算法基于图像序列的帧间运动特性对图像进行分区处理；利用图像子区域的灰度均值进行帧间预测，用来判断图像序列中被遮挡图像帧和可能的遮挡阴影区域；利用空域滤波器剔除误检区域，确定阴影区域。该算法实时性好，易于工程实现。

Shadowed area will appear in the displayed image when the field of view of a surveillance system is obscured, and it influences the analysis and further processing of the image. A real time shadow detection algorithm is presented to solve this problem. Firstly, the image is divided into image blocks based on inter-frame movement feature of sequence images in this algorithm. Secondly, the algorithm judges if this image frame is obscured and detects the possible shadowed area with the inter-frame predictor based on the gray mean of the image block. Finally, the shadow area is confirmed with a space domain filter for eliminating the erroneous detection areas. The experiment shows that this algorithm is real time and feasible.