如何拍摄剪影效果

http://www.eportfolios.cn/node/1498

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查看以下剪影效果，思考剪影效果照片有何特点，如何才能拍摄出剪影效果的照片？<br />
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<iframe frameborder="0" scrolling="no" title="Preview" marginheight="0" marginwidth="0" style="width: 98px; height: 115px; padding: 0pt; background-color: rgb(252, 252, 252);" src="http://cid-851bc636709107db.skydrive.live.com/embedicon.aspx/mirror%20image%20and%20inverted%20image/silhouette"></iframe><br />
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观看剪影效果照片：<a href="http://cid-851bc636709107db.skydrive.live.com/play.aspx/mirror%20image%20and%20inverted%20image/silhouette?ref=1">点击查看</a><br />
<iframe frameborder="0" scrolling="no" title="Preview" marginheight="0" marginwidth="0" style="width: 122px; height: 137px; padding: 0pt; background-color: rgb(252, 252, 252);" src="http://cid-851bc636709107db.skydrive.live.com/embedalbum.aspx/silhouette"></iframe>