Abstract: Watermarking is an important field for copyrights of digital media and owner authentication. Reversible image watermarking method based on contrast mapping accomplishes different transform applied on pixels and their least significant bits are used for data embedding. It is invertible if the least significant bits of the transformed pixels are lost during data embedding. Reversible contrast mapping offers high embedding data at low visual distortion. Distortion caused due to embedding should be made small. This lead to the original and the watermarked image equivalent so that embedded data remains imperceptible on visualization. This type of imperceptible distortion is not acceptable in medical and military image. This has led to an interest on reversible watermarking, where the embedded watermark is not only extracted but also perfect restoration of the original signal is possible from the watermarked image. Low computation cost and ease of semicustom make it attractive for real time implementation. The design and implementation of a FPGA (Field Programmable Gate Array) based architecture using image watermarking algorithm is done on host image. Security level offered by the watermarking techniques based on hardware is higher than the software based watermarking techniques. Distortion caused due to embedding should be made small as much as possible, so distortion control technique is used based on threshold values.

Keywords: Reversible image watermarking, Reversible contrast mapping, Semicustom, Secret image.