关键词: 改进的尺度不变特征变换（SIFT）, 水印, 几何攻击, 奇偶量化, 降维

Abstract: An effective against geometric attack robustness of digital watermarking algorithm based on improved SIFT（Scale Invariant Feature Transform） is presented.It achieves watermark synchronization using improved Scale-Invariant Feature Transform；watermark is embedded in cirque，using odd-even quantization in spatial domain and is extracted from an odd-even detector.Simulation results show that improved SIFT can reduce the matching dimension of feature point，improve the matching rate.And the proposed scheme achieves good image quality and it is robust to geometric attacks as well as traditional signal operations.

Key words: improved Scale Invariant Feature Transform（SIFT）, watermarking, geometric attack, odd-even quantization, reduce dimensionality