Thumbnail can greatly increase the efficiency of browsing pictures,videos and other image resources and improve the user experience prominently.Map service is a kind of graphic resource coupling spatial information and representation scale,its crafting,retrieval and management will not function well without the support of thumbnail.Sophisticated designed thumbnails bring users vivid first impressions and help users make efficient exploration.On the contrast,coarse thumbnail cause negative emotion and discourage users to explore the map service positively.Inspired by video summarization,key position and key scale of web map service were proposed.Meanwhile,corresponding quantitative measures and an automatic algorithm were drawn up and implemented.With the help of this algorithm,poor visual quality,lack of map information and low automation of current thumbnails was solved successfully.Information entropy was used to determine areas richer in content and tran-scale similarity was calculated to judge at which scale the appearance of the map service has changed drastically,and finally a series of static pictures were extracted which can represent the content of the map service.Experimental results show that this method produced medium-sized,content-rich and well-representative thumbnails which effectively reflect the content and appearance of map service.%缩略图可显著提高图片和视频等图形图像资源的展现效率,有效改善信息检索过程中的用户体验.地图服务是一种耦合空间和尺度信息的图像资源,其设计创作、检索筛选和存储管理均需要缩略图的支撑.设计精巧的缩略图带给人良好、鲜活的第一印象,帮助用户实现高效的交互与探索;粗糙凌乱的缩略图则让用户产生抵触情绪,打消其继续探索地图服务的主动性.本文借鉴视频关键帧的思路并结合地图表达特点,提出了地图服务关键位置和关键尺度的概念,并设计了相应的量化指标和提取算法,重点解决了缩略图视觉效果不佳、地图信息量不足和自动化程度不高等问题.算法基于信息量识别地图中内容丰富的关键位置,然后利用跨比例尺相似度判断发生显著变化的关键尺度,最后自动筛选出若干张代表地图服务内容的缩略图.试验表明本方法提取的缩略图数量适中、内容丰富、代表性强,可高度还原地图服务的内容构成和外观样式.
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