Research On Partial Encryption Of Color Image Based On Quaternion And Application In Remote Sensing Image

Color remote sensing image which is important data source of space and geographic information, has been widely applied to many fields, such as military reconnaissance, aerospace, agricultural production, weather forecasting, ocean detection and so on. With the rapid development and popularization of information technology, it is so convenient and quick to browse and transmit image data on the Internet, however the open environment of network has also brought problems about secure transmission of color remote sensing image. Partial encryption schemes of color image which can not only improve encryption efficiency and reduce the system load, but also meet the requirements of different security applications, has important research value and significance. In this thesis, partial encryption of color image based on quaternion is studied and applied in remote sensing image. The main content is as follows:Firstly, from the view of partially encrypted application requirements of image, three partial encryption models of color image are concluded, i.e. partial encryption models based on blocking or target, image degradation and security. The existing partial encryption schemes of color image are summarized as two-dimension plane, block-tree mapped, and three-dimension space three types, their advantages and disadvantages are introduced and analyzed. Finally it is pointed out that the quaternion-based three-dimension space partial encryption is the possible hot research field.Secondly, based on quaternion discrete Cosine transform (QDCT), a partial encryption algorithm for color image is presented. The algebraic relationship between QDCT and discrete Cosine transform (DCT) is analyzed, and the quantization table and encoding method of color image QDCT coefficients are proposed. The The analysis results of simulation and safety performance show that the algorithm makes the encrypted image invisible, reduces the amount of encryption data and transmission data, and evens the pixel distribution of original image.Thirdly, based on quaternion wavelet transform (QWT), partial encryption algorithm for color image is proposed. The embedded zerotree wavelet (EZW) is improved to embedded zerotree quaternion wavelet (EZQW), which is applied to the amplitude coding. By analyzing the histogram of the quaternion wavelet phase, we propose the phase quantization method, and then implements the encoding and encryption of the quantizied phase with the combination of the run-length encoding (RLE) and custom coding method. Experimental results show that the proposed algorithm realizes the excellent encryption performance, and owns high sensitive key and large key space, which can resist against most key-attack methods.