Digital image watermarking method using between-class variance

We propose a low-complexity, pixel-based watermarking method utilizing the edge areas in an image. In this method, an image is divided into blocks and the blocks are classified as edge blocks and non-edge blocks. The histogram of pixels in an edge block is a bi-modal distribution which has two peaks. Therefore, these pixels are further classified into two classes named “high peak class” and “low peak class”. Then, a bit of the watermark is embedded by controlling the between-class variance by changing the pixel values in each class of the edge block. We utilized the discriminant analysis method for deciding a threshold and controlling the between-class variance. The proposed method can improve the image quality while maintaining robustness against compression and smoothing. In this paper, we evaluated the image quality of watermarked images using PSNR and SSIM. We also evaluated robustness against JPEG compression and Gaussian filtering.