Flip-Invariant SIFT for Copy and Object Detection

• Published in: IEEE transactions on image processing 2013-03, Vol.22 (3), p.980-991
• Main Authors: ZHAO, Wan-Lei, NGO, Chong-Wah
• Format: Article
• Language: English
• Subjects: Algorithms; Applied sciences; Artificial Intelligence; Clocks; Cryptography; Detection, estimation, filtering, equalization, prediction; Detectors; Estimating; Exact sciences and technology; Feature extraction; Filtering; Flip invariant scale-invariant feature transform (SIFT); geometric verification; Histograms; Image Enhancement - methods; Image Interpretation, Computer-Assisted - methods; Image processing; Information, signal and communications theory; Invariants; Object detection; Object recognition; Pattern recognition; Pattern Recognition, Automated - methods; Preserves; Reproducibility of Results; Reproduction; Sensitivity and Specificity; Signal and communications theory; Signal processing; Signal, noise; Studies; Telecommunications and information theory; Transformations; Vectors; video copy detection
• ISSN: 1057-7149; 1941-0042
• DOI: 10.1109/TIP.2012.2226043

Scale-invariant feature transform (SIFT) feature has been widely accepted as an effective local keypoint descriptor for its invariance to rotation, scale, and lighting changes in images. However, it is also well known that SIFT, which is derived from directionally sensitive gradient fields, is not flip invariant. In real-world applications, flip or flip-like transformations are commonly observed in images due to artificial flipping, opposite capturing viewpoint, or symmetric patterns of objects. This paper proposes a new descriptor, named flip-invariant SIFT (or F-SIFT), that preserves the original properties of SIFT while being tolerant to flips. F-SIFT starts by estimating the dominant curl of a local patch and then geometrically normalizes the patch by flipping before the computation of SIFT. We demonstrate the power of F-SIFT on three tasks: large-scale video copy detection, object recognition, and detection. In copy detection, a framework, which smartly indices the flip properties of F-SIFT for rapid filtering and weak geometric checking, is proposed. F-SIFT not only significantly improves the detection accuracy of SIFT, but also leads to a more than 50% savings in computational cost. In object recognition, we demonstrate the superiority of F-SIFT in dealing with flip transformation by comparing it to seven other descriptors. In object detection, we further show the ability of F-SIFT in describing symmetric objects. Consistent improvement across different kinds of keypoint detectors is observed for F-SIFT over the original SIFT.