Reversible data hiding by reserving room

Reversible data hiding by reserving room becomes more prominent, since the original cover is restored without any loss after the hidden data is extracted. Encryption is performed to provide the confidentiality for the image content. In this project,space for embedding data is reserved with pairwise prediction error expansion(PEE) and histogram shift before encryption has been performed, so that data hider can reversibly embed data into encrypted image easily. Image redundancy isbetter exploited in prediction error expansion which leads to superior performance. But in current PEE based method, correlation within prediction error is not better exploited. Hence to better exploit the correlation among prediction errors, two prediction errors are jointly considered. Then the embedding is based on the prediction error pair and its 2D prediction-error histogram, which leads to improved performance. Secret data extraction and image restoration in this method is free of any errors. By this method, high PSNR is achieved than any other method in reversible data hiding.