Reversible watermarking is very popular in medical and military applications. Reversible Contrast Mapping (RCM) can achieve 100% original image as well as watermark. This method is simple equation that can be applied to pairs of pixels. Here we have compared Coltuc and Chassery RCM equation with its double RCM equation. We found that though double RCM equation is suitable for reversible watermarking, its embedding capacity and quality decrease. But for some pairs of pixels (with which normal RCM does not work), double RCM is completely invertible. The double RCM equation is not suitable against attacks. The data space occupied by Least Significant Bits (LSBs) is suitable for data hiding. But our proposed double RCM method is suitable for all images.

The reversible watermarking technique is an exact recovery of the original watermark and original image. This can be done on images, audios or letters. Hidden data may be a history of a patient in medical images, secret map in military applications, or a logo in case of image authentication.

Many reversible watermarking techniques have been introduced. Honsinger et al. (2001) presented a method using addition modulo 256. Kalker and Willems (2002) provided some theoretical capacity limits of lossless data compression-based reversible data embedding. A high capacity reversible data-embedding algorithm with low distortion was proposed by Celik et al. (2002). Lossless authentication algorithm using lossless bit-plane compression was proposed by Fridrich et al. (2002). A reversible data embedding method using difference expansion was proposed by Tian (2003).

The existing lossless data hiding algorithms were classified into three categories by Xuan et al. (2004). Histogram modification method is a very popular method of reversible watermarking. Initially, Ni et al. (2006) presented this method, and Rajendra and Navnath (2012) presented a modified version of the histogram shifting method. Dinu and Jean-Marc (2007) recently proposed reversible watermarking using Reversible Contrast Mapping (RCM) method. Studies by Tzu-Chuen and Ying Hsuan (2008) and Yeh-Shun and Ran-Zan (2010), which are related to RCM method, are very important references. Reversible watermarking algorithm by circular interpretation of bijective transformations was proposed by De Vleeschouwer et al. (2003). Inherent correlation among the neighboring pixels in an image region using a predictor was proposed by Thodi and Rodrguez (2002). Compression-based techniques embed extra required information for recovering the host image and the experiment results demonstrate that the technique can result in good quality of stego image with high embedding capacity. However, the algorithm of reversible watermarking is very complicated as compared to watermarking. The technique has been widely used for image authentication, ownership protection, access control, metadata embed, annotation and so on.

Telecommunications Journal, Speech Noise Elimination, Traditional Spectrum Subtraction, Communication Systems, Speech Processing Algorithms, Signal Processing, Noise Reduction Techniques, Voice Activity Detection, Spectrum Subtraction Method, Signal to Noise Ratios, Cockpit Voice Recorder, Musical Noise.