Journal of Image and Signal Processing
Vol.3 No.04(2014), Article ID:14258,7 pages
DOI:10.12677/JISP.2014.34014

Research on Chaos Encryption Method in Image DCT Domain

Ying Chu1, Xiaoman Wang1, Peng Liu1, Shuchang Liu1, Zhiqiang Han2

1Department of Electronic Information, Changchun University of Science and Technology, Changchun

2Department of Foundation, Air Force Dalian Communication Sergeant Academy, Dalian

Email: chuying0926@126.com

Received: Jun. 26th, 2014; revised: Jul. 4th, 2014; accepted: Aug. 1st, 2014

ABSTRACT

In this paper, we suggest one chaos image encryption method in DCT domain according to the characteristics of JPEG image compression. The chaotic models used in this algorithm are Logistic mapping and Chebyshev mapping. The one-dimensional Logistic mapping is used to generate a chaotic sequence which is considered as control matrix for scrambling DCT coefficient matrix. According to the JPEG image compression standard, scrambling the DCT coefficient matrix by 8 × 8 pixels in blocks can make the low-frequency composition remain in the upper-left corner of the DCT matrix. When we implement XOR operation between chaotic sequence and DCT coefficient matrix, we only encrypt interested DCT coefficients. Using the above two methods, we not only improve the encryption speed of the image, but also avoid low image compression rates due to scrambling the image encryption method. At last, we use the two chaotic models to generate sign matrix. The simulation results show that the algorithm has good encryption effects, fast encryption speed, and high security.

Keywords:Image Compression, DCT, Logistic Mapping, Compression Rates

1长春理工大学，电信学院，长春

2空军大连通信士官学校，基础部，大连

Email: chuying0926@126.com

1. 引言

2. 算法实现

2.1. JPEG图像压缩算法特征分析

JPEG算法[2] -[4] 框图如图1所示，假设原始图像大小为M*N。压缩时，将原始图像数据分成数据单元矩阵。

Figure 1. JPEG agrithm frame

Figure 2. Zig-Zag rank

2.2. 混沌加密算法设计

2.2.1. 置乱矩阵与变换矩阵的生成

Logistic映射[6] 是一个典型非线性混沌方程，它起源于一个人口统计的动力学系统，虽然简单却体现

Figure 3. Curve: system result of standard experiment

(1)

2.2.2. 符号矩阵的生成

(2)

(3)

2.3. 加密算法实现

3. 仿真实验与分析

(4)

1) I = imread('cameraman.tif'); I = im2double(I);

2) I1 = 255*I -128; T = dctmtx(8);

3) B = blkproc(I1,[8 8],'P1*x*P2',T,T');

5) B2 = round (0.5*B1);

(a)(b)(c)(d)(e)(f)(g)(h)

Figure 4. Image encryption and decryption simulation results. (a) Original image, (b) DCT of Original image, (c) DCT of Encryption image, (d) Encryption image, (e) Right decryption, (f) Wrong decryption, (g) Histogram of original image, (h) Histogram of original image

(5)

(6)

(7)

(8)

(9)

Figure 5. Pixel value difference distributing of two Ciphertexts

(a)(b)(c)(d)

Figure 6. Decryption result of cryptograph with noise. (a) cryptograph with pepper noise, (b) Encryption of (a), (c) cryptograph with guassian noise, (d) Encryption of (c)

Table 1. The correction coefficients of plaintext image and cryptograph image

Table 2. Compare of operation and compression ratio

4. 结束语

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