基于离散余弦变换的图像加密效果评估方法

不动点比,图像相似度等是传统的图像加密效果评估方法,传统方法具有局限性和不准确性。文中提出一种基于离散余弦变换的图像加密效果评估方法,利用离散余弦变换(DCT)把图像从时域变换到频域,同时分析图像的能量分布状况,以此评估图像的加密效果;计算明文图像和密文图像的频谱系数差值,用该差值构造差值系数矩阵,最后计算图像信息熵,通过熵值大小判断图像加密效果,得到新的图像加密效果评估方法。通过不同图像加密方法对同一图像进行加密,用新方法进行加密评估;对同一图像分别采用新的加密评估方法与传统方法进行评估,比较评估结果准确性等实验,验证了新方法的有效性。提出的加密评估方法改善了传统加密评估方法的局限性,提高了评估准确性,评估结果也与人眼观察效果基本一致。

A Novel Image Encryption Performance Evaluation Based on Discrete Cosine Transform

Traditional image encryption performance evaluation methods,such as fixed point ratio and image similarity,have limitations and inaccuracy. A novel image encryption performance evaluation has been presented. The discrete cosine transform(DCT) is used to transform the image from time domain to frequency domain,and the energy distribution of the image is analyzed to evaluate the image encryption effect. The DCT coefficient difference between plain-text and cipher-text image is calculated to construct the difference coefficient matrix. Then the information entropy is employed to measure the encryption performance. The same image is encrypted by different image encryption methods,and the novel method is used for encryption evaluation. The effectiveness of the novel method is verified by comparing the accuracy of the new method with that of the traditional method. The proposed encryption evaluation method improves the limitation of the traditional encryption evaluation method and the accuracy of the evaluation,and the evaluation results are basically consistent with the observation effect of human eyes.