数字水印检测中剪裁图像的配准

Registration of Cropped Image for Watermark Detection

围绕剪裁图像中数字水印的检测问题讨论剪裁参数的估计 .利用离散 Fourier变换的旋转不变性 ,通过对边缘图像 DFT沿不同方向的积分并采用差分相关技术 ,可准确估计剪裁图像的倾斜角 .二维相关运算则给出剪裁图像在原图像中所处位置 ,从而将图像配准 ,实现可靠的水印检测 .

Aimed at detection of digital watermark from cropped images, a method for image registration is described. Based on the rotational invariant property of the Fourier transform, the DFT of Sobel edge is integrated along radials at different angles, and cross-correlation calculated between the difference sequences of the cropped and the original images. In this way, the tilting angle is calculated. The offset is then obtained by cross-correlating the cropped and tilt-corrected image with the original, making available the necessary parameters for watermark extraction.