A high payload reversible watermarking scheme based-on OFDM-CDMA

摘要

One of the disadvantages of the application of watermarking is it causes permanent distortion to the original image after watermark is removed, especially, if the watermark is embedded in large quantities. On the sensitive application such as medical or military imaging, distortion in the image may cause misunderstandings in interpreting the information, therefore a reversible watermarking method based on OFDM-CDMA is proposed in this paper. OFDM-CDMA method is a combination of OFDM and CDMA methods. In this method, the watermark is converted to parallel streams and multiplexed to streamline the bandwidth so it can provide a high data payload. Then, each sequence of the parallel watermark is multiplied by spreading codes to reinforce the orthogonality of each sequence, so it can minimize the error between the sequences. The resulting error rate affects the quality of the recovered image. From the results of this study shows that by using a watermarking system based on OFDM-CDMA with the same amount of payload, the smaller watermark power is used the better level of the visual quality image is produced both on the watermarked image and the recovered image. However, to obtain optimum results, besides getting a good level of visual quality while maintaining the error rate to keep them small, of some tested watermark power values, the most optimal watermark power value is 0.08 with a data payload 0.1563 to 0.9766 bpp.