AN ASYMPTOTICALLY UNIFORMLY REVERSIBLE DATA HIDING IN ENCRYPTED IMAGES BY PIXEL PAIR MATCHING TECHNIQUES

The reversible data hiding (RDH) in encrypted images, since it maintains the excellent property that the original cover can be losslessly recovered after embedded data is extracted while protecting the image content’s confidentiality. All previous methods embed data by reversibly vacating room from the encrypted images, which may be subject to some errors on data extraction and/or image restoration. A novel method called pixel pair matching which has the advantage of inserting the data without changing the image content, and thus it is easy for the data hider to reversibly embed data in the encrypted image. The proposed method can achieve real reversibility, ie. data extraction and image recovery are free of any error. The distortion caused by data embedding is called the embedding distortion. A good data-hiding method should be capable of evading visual and statistical detection while providing an adjustable payload. The LSB method employ one pixel as an embedding unit, and conceal data into the right-most LSBs.To achieve satisfactory hiding capacity Exploiting modification direction (EMD) and Diamond Encoding (DE) are two data-hiding methods proposed recently based on PPM. The maximum capacity of EMD is 1.161 bpp and DE extends the payload of EMD by embedding digits in a larger notational system. This method offers lower distortion than DE by providing more compact neighborhood sets and allowing embedded digits in any notational system. Data-hiding method based on PPM.DE greatly enhances the payload of EMD while preserving acceptable stego image quality. The image preprocessing  and binary operation of  two pixels are scanned as an embedding unit and a specially designed neighborhood set is employed to embed message digits with a smallest notational system. PPM allows users to select digits in any notational system for data embedding, and thus achieves a better image quality