外文翻譯--使用糾錯碼的基于人類視覺系統(tǒng)的數(shù)字水印方案（英文）

1、Tamkang Journal of Science and Engineering, Vol. 4, No. 3, pp. 201-208 (2001) 201 Digital Image Multiresolution Watermark Based on Human Visual System Using Error Correcting

2、 Code Ching-Tang Hsieh and Yeh-Kuang Wu Department of Electrical Engineering Tamkang University Tamsui, Taipei, Taiwan 251, R.O.C. E-mail: hsieh@ee.tku.edu.tw Abstract Digital watermarking has been proposed as a w

3、ay to claim protection. In this paper, we try to use the error-correcting code skill, the multiresolution of wavelet transformation, and the human visual system to improve the traditional watermarking. Error-correctin

4、g based watermarking will have the property that corrects errors of the extracted watermark automatically. The HVS (Human Visual System) model will be presented to investigate perceptually characteristic parts of hum

5、an (e.g. intensity or hue) and how to insert the watermark into the original data, where the perceptual sensitivity of human is relatively low. A multiresolution watermarking based on the wavelet transformation is sel

6、ected in each frequency band of the Discrete Wavelet Transform (DWT) domain and therefore it can resist the destruction of image processing. In our experiments, the results show that the robustness of a watermark with

7、 ECC (Error Correct Coding) is much better than the traditional one without ECC. Key Words: DWT, Watermark, HVS, Error-correcting Code, BCH 1. Introduction The rapid development of Internet introduces a new set of chal

8、lenging problems regarding security. One of the most significant problems is to prevent unauthorized copying of digital production from distribution. Digital watermarking has provided a powerful way to claim intellec

9、tual protection [3,6,7,10,11,23-25]. Watermark must have two most important properties: transparency and robustness. ? Transparency refers to the perceptual quality of the watermarked data. The watermark should be i

10、nvisible over all types. ? The digital watermark is still presented in the image after distortion and the watermark detector can detect it. Ideally, the amount of image distortion necessary to remove the watermark s

11、hould degrade the desired image quality to the point of becoming commercially valueless. It is called the robustness of digital watermark to image processing. The common distortion of signal processing includes lossy

12、 compression (in particular JPEG), resampling, requantization, image enhancement, cropping, etc. A key point of the watermarking technique is the trade-off between the transparency and the robustness. We must determi

13、ne where to insert watermark and how to enhance the robustness of the watermark. In this paper a wavelet based watermarking method using the HVS [11,24] is presented. In [14], Lee adopted the RS code (Reed-Solomon co

14、de) to generate ECC codewords, and regarded the codeword’s parities as watermark. They used watermark to recover the damaged image. But from the viewpoint of intellectual protection, the watermark is more impor

15、tant than the image, while the image quality is maintained. They did not handle the watermark. We proposed an idea for enhancing the robustness of extracted watermarks. Watermark can be treated as a transmitted sign

16、al, while the destruction from attackers is regarded as a noisy distortion in channel. According to the viewpoint mentioned above, we provide an idea using ECC to Digital Image Multiresolution Watermark Based on Human

17、 Visual System Using Error Correcting Code 203 Original imageWavelet coeff.Watermarked imageMTF EstimatorDWTModified Wavelet coeff.IDWTWatermarkError-correction encodingWatermark insertionFigure 2. Digital w

18、atermarking method First, we use a pseudo-random sequence as watermark W. We decompose the original image by DWT in three levels to obtain the wavelet coefficient in each band as shown in Figure 3. In order to enhanc

19、e the transparency of watermark, we multiply ith band by different weighting value [11,19,24]. The ith weighting value i w is the integral of a Modulation Transfer Function (MTF) over the frequency interval in each

20、band: ( ) ∫∫ =iiWB s sWB si df f Hdf w(3) where ( ) s f Hand i WB are MTF and the bandwidth of ith band respectively. ( ) ( ) ( ) ts s s sf rf q p f H ? + = exp(4) ? ?? ? ?? = + i i i WB 21 , 211(5) The procedure of

21、insertion is described as follows: Step 1.We decompose the original image Y with a three-level DWT to obtain the wavelet coefficient y(m,n). The parameter m, n, represent the spatial location of each pixel in the de

22、composed image. Step 2.Calculate the weighting value i w of each band according to equation (3), (4) and (5). The parameter p, q, r, s and t are constants in our experiment (p=2.6, q=0.192, r=s=0.114, t=1.1). Step3

23、.We encode the watermark W using ECC algorithm to obtain W ′ . Set a threshold T. Step 4.If the absolute magnitude of wavelet coefficient is larger than the threshold T (i.e. ≥ ) , ( n m y T) we insert the watermark i

24、nto the wavelet coefficient y(m,n) according to the order shown in Figure 4.: (6) where ( ) n m y , ′ and α are modified wavelet coefficient and parameter to control the level of the watermark respectively. Step 5.Fi

25、nally, we take inverse DWT of the modified wavelet coefficient to obtain watermarked image Y ′. Figure 3. The decomposed Lena in three levels Figure 4. The order of inserting the watermark 4. Watermark Detection We can

26、 extract the watermark X essentially taking the inverse steps described in section 3. The extraction of watermark requires both original image Y and watermarked imageY ′. For watermark detection, a similarity measure

27、 ( ) W X sim ,used in [6] is defined by eq.5: ( )X XW X W X sim ?? = ,(5) where ‘ ? ’ denotes the inner product of two vectors. 5. System Evaluation We use three test images in our experiments of which sizes are all 512

28、 ×512 in pixels. The quantity of watermark actually inserted is 5000. The parameter α is set to 0.15 and a smaller value of 0.01α is set for the lowest frequency band LL3. The threshold T is ( ) ( ) ( ) W n m y