Digital Image Scrambling Degree Evaluation Mothed Study Based On Frequency Of Gray Levels

Dramatic visualization of image information has become the most important means of communication. The preservation of image data has been attached much importance by the society.Experts abroad and at home have proposed many Image Encrypting methods. This transformation of Image Encrypting can be sorted into three groups: (1) the Image Encrypting only by changing the location of pels; (2) the Image Encrypting only by changing the pels Gray Levels; (3) the Image Encrypting by changing both of location of pels and pels Gray Levels. The measurement of distribution of Digital Image Scrambling algorithm is an essential aspect of evaluating Digital Image Scrambling algorithm.Digital Watermark technique is also a chief method in preserving image data, the measurement of Scrambling Degree has a significant guiding effect on the problem of the strength of robustness in Watermark Algorithm.This thesis has analyzed the features of the best effects of Digital Image Scrambling, such conclusions have been achieved: equality and uniformaty of pels distribution post-scrambling are the main features of the best effects of Digital Image Scrambling. The equality and uniformity of pels distribution refers to every Degree Of Gray Levels for each optional area of an image, its frequency in the area is eaual to the frequency in the image. Therefore, the thesis has given the definition of the best effects of Digital Image Scrambling.Using the best effects of digital image scrambling as parameters, This thesis has brought forward a evaluation method in Digital Image Scrambling Degree which based on the Frequency of Gray Levels, at the same time, relevant study on its characteristic has been carried out. In this way, a solid method has been provided. Emulational experiments were carried out by taking MATLAB as a research tool.At first, one of the three types of Image Encrypting methods was selected as a representative. Secondly, This thesis used the three methods mentioned above to scramble to the same image and get different scrambling effects of one definite image. Finally, This thesis used the three Image Encrypting methods above to scramble to different images and got three different kinds of effects. The results of the experiment have suggested that the evaluation method of Digital Image Scrambling Degree can describe the effects of scrambling of images objectively. It has the advantages as following: (1) Consistency: the resulting Digital Image Scrambling Degree is accordant with visual subjective evaluation; (2) High-generalization: it is adaptable to the images only by changing the location of pels, the images only by changing the pels Gray Levels, and the images by changing both of location of pels and pels Gray Levels; (3) No relationship with previous images : as for the same method of Image Encrypting, the degree of scrambling would not change a lot for the sake of the transformation of the previous image.