Color Image Information Hiding Technology Based On Quaternion Theory

In this dissertation, color image information hiding technology include color image encryption,steganography and color image watermarking using quaternion is proposed. The color image can be described as a quaternion matrix, by which color images can be processed as a whole, rather than as separated color components in three channels.The emphases in this thesis are summarized as following:1,A new method for color-image encryption using Discrete Quaternion Fourier Transforms (DQFT) combined with doubled random-phase encryption as used in the optical implementation is proposed, by which color images can be processed as a whole, rather than as separated color components in three channels, so that the complexity of the encryption system can be effectively reduced without any reduction of its security. The principle of both encryption and decryption is detailed and the robustness of the system has been examined experimentally.2,A new method for color image steganography using Discrete Quaternion Fourier Transforms(DQFT) is proposed. The host color image should be transformed to the DQFT domain, and the secret image should be encrypted first and then the encrypted color image can be embedded into the DQFT domain of the host image.3,A new method for color image watermarking using Discrete Quaternion Cosine Transforms (DQCT) is proposed. The watermark image can be embedded in the DQCT domain of the host color image. Experimental results show that this method has good resistance to JPEG compression and is robust against Gaussian noise,salt & pepper noise and image scaling attack.