Reversible Data Hiding Algorithms For Encrypted Images Based On Pixel Prediction And Bit-plane Coding

In recent years,cloud computing technology has developed rapidly,and a large number of cloud service providers have launched cloud storage services for users.These cloud storage services meet users' needs for cross-platform and multi-terminal file storage,backup and sharing,and bring great convenience to users.Due to the increasingly severe network security situation and people's increasing awareness of privacy protection,before users upload multimedia data such as images to the cloud,they are often encrypted to protect private information.With the increasing number of encrypted images in the cloud,how to effectively manage and apply encrypted images has become an urgent problem to be solved in the field of cloud services and information security.To this end,researchers propose to study the reversible data hiding algorithm of encrypted images,which can realize image retrieval,identity authentication and copyright protection by embedding additional daata in encrypted images.At present,designing algorithms with high embedding capacity is an important research task in the research on reversible data hiding in encrypted images.This dissertation takes encrypted images as the research object,and uses pixel prediction,bitplane structure information coding and quad-tree coding to study reversible data hiding in encrypted images.Two effective data hiding algorithms are designed,namely,reversible data hiding algorithm in encrypted images based on bit-plane structure information coding and reversible data hiding algorithm in encrypted image based on bit-plane quad-tree coding.The main achievements of this dissertation are summarized as follows:(1)A reversible data hiding algorithm in encrypted images based on bit-plane structure information coding is proposed.Since the prediction error histogram obeys a Laplace-like distribution centered at or close to0,after decomposing the absolute value of the prediction errors into eight bit-planes,most of the elements constituting each bit-plane are 0.Aiming at this characteristic,a reversible data hiding algorithm for encrypted images based on bit-plane structure information coding is proposed.The algorithm first uses the pixel predictor to predict the original image to obtain its prediction error map,and next divides the prediction error map into image blocks of equal size.Then,the eight bitplanes of each block are divided into two kinds to construct the bit-plane structure information,and the eight bit-planes are re-encoded according to the structure information to vacating the embedding room.Finally,the additional data is embedded and extracted according to the mark of the specified position in the image block.The experimental results show that the algorithm can not only ensure the correct extraction of additional data and the lossless recovery of the original image,but also achieve a large performance improvement in terms of embedding capacity,which is better than a variety of reversible data hiding algorithms for encrypted images.(2)A reversible data hiding algorithm in encrypted images based on bit-plane quad-tree coding is proposed.Quad-tree is a tree-like data structure,and each node can have at most four child nodes.Quadtree decomposition divides two-dimensional space by recursively subdividing it into four quadrants or rectangular regions,and is widely used in fields such as image compression,edge detection,and data indexing.In this work,a bit-plane oriented quad-tree coding scheme is designed using quad-tree decomposition technology.According to the scheme,a high-capacity reversible data hiding algorithm in encrypted images is proposed.The algorithm first performs pixel prediction on the cover image to obtain the prediction error map,and uses the consistency criterion to perform quad-tree decomposition on the eight bit planes of the prediction error.The decomposed image blocks are divided into four categories,and the corresponding bit plane block classification label map is generated.The bit-plane block classification map is then converted into a quad-tree,which is efficiently compressed by two different quad-tree encoding schemes to vacating embedding room.Finally,the encoded result is reconstructed back to the image,and the additional data is embedded by the method of bit replacement.The algorithm realizes the separable operation of data extraction and image restoration.The experimental results show that the performance of the algorithm in terms of embedding capacity is significantly improved,and it can meet the needs of high capacity and separable application scenarios.