这个链接是将1000类分成大类：http://blog.csdn.net/zhangjunbob/article/details/53258524
imagenet编号和具体类别对应的表：https://gist.github.com/aaronpolhamus/964a4411c0906315deb9f4a3723aac57
rcnn中读取imagenet object前30类的代码：https://github.com/rbgirshick/rcnn/blob/ilsvrc/imdb/imdb_from_ilsvrc13.m
https://github.com/rbgirshick/rcnn/blob/ilsvrc/imdb/roidb_from_ilsvrc13.m
