A reversible image watermarking scheme based on modified integer-to-integer discrete wavelet transform and CDMA algorithm

This paper presents a secure and large capacity reversible watermarking scheme based on modified integer-to-integer discrete wavelet transform (iDWT) and code division multiple access (CDMA) algorithms. In this scheme, the watermark data are spread by orthogonal spreading sequence and then embedded into wavelet domain, which can only be extracted with same spreading codes and be removed after extraction to recover the original image exactly. The iDWT is modified with the method of exchanging the positions of nearby pixels to generate positive wavelet coefficients, through which the length of the spreading sequence is cut down and the embedding capacity enhanced effectively. The influence of the length of different spreading sequences on watermark capacity is discussed and optimal length of orthogonal spreading sequence is obtained to achieve balance between the watermark capacity and image distortion. Performance comparison with some state-of-art reversible watermarking schemes shows that the proposed scheme achieves higher embedding capacity while maintaining image distortion at lower level.