Combining attention and recognition for rapid scene analysis

Bottom-up visual attention allows primates to quickly select regions of an image that contain salient objects. In artificial systems, restricting the task of object recognition to these regions allows faster recognition and unsupervised learning of multiple objects in cluttered scenes. A problem is that objects superficially dissimilar to the target are given the same consideration in recognition as similar objects. Here we investigate rapid pruning of the recognition search space using the already-computed low-level features that guide attention. Itti and Koch’s bottom-up visual attention algorithm selects salient locations based on low-level features such as contrast, orientation, color, and intensity. Lowe’s SIFT recognition algorithm then extracts a signature of the attended object, for comparison with the object database. The database search is prioritized for objects which better match the low-level features used to guide attention to the current candidate for recognition. The SIFT signatures of prioritized database objects are then checked for match against the attended candidate. By comparing performance of Lowe’s recognition algorithm and Itti and Koch’s bottom-up attention model with or without search space pruning, we demonstrate that our pruning approach improves the speed of object recognition in complex natural scenes.