Robust and reversible color image watermarking based on DFT in the spatial domain

With the purpose of protecting the copyright and integrity of color images, a robust and reversible color image watermarking algorithm in the spatial domain fusing discrete Fourier transform (DFT) is proposed. Based on the relationship between the direct current (DC) component of DFT and the spatial-domain pixel values, the proposed quantization technology is used to embed and extract the watermark in this paper. Firstly, color images are represented in RGB color space, and the red, green, and blue channels of the host image are preprocessed for obtaining image blocks of size 2 x 2 and that of the watermark image are preprocessed for obtaining watermark bit sequences. Secondly, the DC component of DFT in each block is calculated and quantized, and the change of the DC component is assigned to each pixel value by the derived formula. Finally, it is completed to embed a 1-bit watermark into one block in the spatial domain. Meanwhile, a matrix that records the magnitude of the change of pixel value in each block is generated to recover the host image, and the related watermark extraction algorithm is also proposed. The experimental results show that this algorithm can completely extract the watermark and restore the host image without loss under the condition of not being attacked, and it has good invisibility, robustness, security, and embedding payload, particularly its running efficiency is also high.