Global query expansion (GQE): The BoW vectors of the N images at the top of the ranking are averaged together with the BoW of the query to form the new representation for the query.
Local query expansion (LQE): Locations obtained in the local reranking step are used to mask out the background and build the BoW descriptor of only the region of interest of the N-top images in the ranking. These BoW vectors are averaged together with the BoW of the query bounding box to perform a second search.
다른 논문 읽다가 비슷한 용어가 나오길래.. 다름 아닌 MAC 논문임.
"Query expansion (QE). Re-ranking brings positive images at the very top ranked positions. Then, we collect the 5 top-ranked images, merge them with the query vector, and compute their mean. Finally, the similarity to this mean vector is adopted to re-rank once more the top N images."
즉, 일반 결과중에 상위 결과 Top-K 결과가 어느정도 타당성을 가지고 있다면, query+Top-K vector들 평균값을 취해, 새로운 query vector로 사용한다는 의미이다.
참조 paper : "PARTICULAR OBJECT RETRIEVAL WITH INTEGRAL MAX-POOLING OF CNN ACTIVATIONS"
이외 query expansion 알고리즘을 다양하게 존재 - ex) manifold learning
Experiments
instance dataset - landmark data : oxford building, paris building,,,
caffe - vgg16: conv5_1, conv5_2, conv5_3 > best : conv5_1