关键词: 感兴趣区域（ROI）, 聚类有效性指标, 阈值分割, C均值聚类

Abstract: All kinds of clouds are the interests for people in the satellite cloud images.Considering the complexity of cloud image，this paper proposes a weighted FCM method based on the gray level histogram for cloud image segmentation.The ROI is finally acquired after finishing post-process.A general clustering method needs the class number specified by people.This paper implements automatically confirming the optimized class number based on the clustering validity index.Cloud image segmentation is the important step during the process of ROI extraction.This paper combines the weighted idea with FCM to make the clustering more scientific.On the other hand，the clustering object is transformed from pixel to gray level histogram.The modified algorithm executes more efficiently.The experiment result demonstrates the ROI extraction method can classify the image content into six regions of interest：Land，water，stratus，middle cloud，cirrus and cumulonimbus.The results are consistent with the objective facts.

Key words: Region Of Interest（ROI）, clustering validity index, threshold partition, Fuzzy Clustering Method（FCM）