Abstract: A new method of digital watermarking for two-dimensional engineering graphics based on discrete fractional Fourier transform（DFRFT） is presented.In this algorithm，the graphic is divided into blocks，for each block the relative coordinates line of the lines is picked up and a complex signal is constructed.The watermark is embedded into the FRT of the complex signal.Experiment results show that the proposed algorithm is robust against the attacks such as moving，rotation，scaling，and entity deleting or adding，and it is also safe towards illegal information extraction.

Key words: digital watermarking, fractional Fourier transform, two-dimensional engineering graphic

摘要： 提出一种基于离散分数傅里叶变换（DFRFT）的二维工程图数字水印算法。该算法分块提取工程图中线段的相对坐标线构造复值信号量，将水印嵌入复值信号量的分数傅里叶变换频谱（FRT）中。实验表明，该算法对平移、旋转、缩放、部分实体删除或添加等攻击具有良好的鲁棒性，同时具有良好的安全性。

关键词: 数字水印, 离散分数傅里叶变换, 二维工程图