ScanFormer: Referring Expression Comprehension by Iteratively Scanning
Authors: Wei Su, Peihan Miao, Huanzhang Dou, Xi Li

Referring Expression Comprehension (REC) aims to localize the target objects specified by free-form natural language descriptions in images. While state-of-the-art methods achieve impressive performance they perform a dense perception of images which incorporates redundant visual regions unrelated to linguistic queries leading to additional computational overhead. This inspires us to explore a question: can we eliminate linguistic-irrelevant redundant visual regions to improve the efficiency of the model? Existing relevant methods primarily focus on fundamental visual tasks with limited exploration in vision-language fields. To address this we propose a coarse-to-fine iterative perception framework called ScanFormer. It can iteratively exploit the image scale pyramid to extract linguistic-relevant visual patches from top to bottom. In each iteration irrelevant patches are discarded by our designed informativeness prediction. Furthermore we propose a patch selection strategy for discarded patches to accelerate inference. Experiments on widely used datasets namely RefCOCO RefCOCO+ RefCOCOg and ReferItGame verify the effectiveness of our method which can strike a balance between accuracy and efficiency.