Reversible Color Image Watermarking Algorithm using Reverse Contrast Mapping

A reversible digital color image (RGB) watermarking algorithm based upon reversible contrast mapping (RCM) is being discussed in this paper. RCM is a computationally efficient spatial technique that manipulates the pairs of pixels with easy integer mathematics. Unlike other methods such as difference expansion, histogram modification, prediction error expansion along with adaptive pairing etc. and their various modified versions which considers context of a pixel. Involving more pixels may lead to much computational complexity and time. This method doesn’t need a location map to be stored and saves space. At the embedding stage, the color image is divided into three color intensity planes and watermark information can be embedded into each of the three planes. At the decoding stage, obtain the watermark by collecting bits from three (RGB) components. Net amount of data that can be embedded into color image is increased as compared to grayscale images of same size. Hence proposed algorithm gives good embedding capacity(EC). The experimental results show the values of embedding capacity and two quality metrics PSNR & SSIM for various standard test images. The proposed scheme does not need any location map to embed and hence no need of data compression.