Quantum watermarking algorithm for color images

In order to improve the effect of quantum watermarking for color image, In this paper, a new method of embedding and extracting the color watermark image based on the novel enhanced quantum description (NEQR) is proposed. Firstly, the magnitude of the watermark image is adjusted to the same size as the carrier image, then, the carrier image is described as the quantum superposition state by the NEQR scheme and the watermark image is embedded into the carrier image. Two images exist independently, using an auxiliary qubit to switch between each other. Through the implementation of the phase rotation of 24 qubits of describing pixel gray value of the watermark image, the watermark image is scrambled. In the scrambled watermark image, the gray level information of each pixel is a balanced quantum superposition state in which whole watermark image is a uniform white noise after it is measured. Watermark image extraction is the inverse process of embedding process, which can be achieve by using the corresponding conjugate transpose operators of that used in embedding process. The advantage of this method is that it can be run on the future quantum computer, the watermark embedding does not affect the visual effect of the carrier image, and the embedded watermark image has a very good security.