Method And Implementation For Partial Encryption Of Images Based On SPIHT

With the fast development of network and multimedia, the security of image data has been gaining more and more attention. The traditional encryption methods for text data were firstly used to encrypt image, but the encryption efficiency was very low because of the large quantity of image data. As the progress of image compression, encryption of the compressed image was proposed and the encryption efficiency was largely improved. However, when real-time encryption is required, the quantity of compressed image data is still huge. Therefore, a new encryption method for encrypting only parts of the compressed data, namely partial encryption, was proposed recently.. This method is an efficient solution for meeting requirements of both security and real-time encryption..This thesis aims to propose partial image encryption methods utilizing set partitioning in hierarchical trees (SPIHT). SPIHT is an efficient wavelet image compression based on bit plane. The compressed data are highly correlated , and functions of different data are different. That is, some code are significant for decoding whereas the others are not. By theoretical analysis and simulation experiments, two types of SPIHT data are identified as the most important data since they affect the meaning of the other data. A new partial encryption for gray level image is then proposed by encrypting these selected data. This method is then extended to encrypt color image because CSPIHT for color image is very similar to SPIHT..Besides, an improved BSS encryption utilizing SPIHT is proposed to reduce BSS limitations on indirect separation of correlated images and indeterminacy of output magnitude. Because correlation of image can be reduced by SPIHT encoding, and the magnitude of binary SPIHT data can be fully recovered after BSS, the improved method has excellent separation performance. As a result, the quality of decrypted images is only determined by the compression rate of SPIHT.In order to apply image partial encryption method in practice, a software regarding partial encryption of gray level images is designed using VC. The test experiments show the correctness of the software.