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An embedded watermark technique in video for copyright protection You-Ru Lin*, Hui-Yu Huang**, and Wen-Hsing Hsu* *Department of Electrical Engineering, National Tsing Hua University, Taiwan **Department of Computer Science and Information Engineering, National Formosa University, Taiwan, E-mail:[email protected] Abstract As the Internet and storage equipment become more and more populous, the digital data can easy to distribution. The pirate can easy and limitless to copy digital multimedia. Therefore people are more and more attentive the copyright protection for digital multimedia. Digital watermarking is an important emerging technique for copyright protection and authentication. This paper presents a novel videowatermarking algorithm based on block matching algorithm to achieve copyright protection of owner. The watermark is mainly embedded in the uncompressed domain and is detected without the use of the original video information. Our proposed method is easy to perform and can provide an adjustable threshold to obtain the imperceptibility and robustness performance. The obtained results show the robustness of this approach.

1. Introduction In recent years, the digital videos replaced the analogue technology. The computer is integrated with the network and quickly computation and transmission abilities, the distribution of digital media is becoming faster and easier, and requiring less the effort to make the exact copies. Hence, it is difficult to protect copyright ownership. To solve this problem, many methods are developed [1-3]. Digital watermarking is a favorable method for copyright protection of the multimedia. It is the information to be embedded into the digital products which can be text information, image information, audio information, etc. A secure watermark must be able to combat adversary attacks such as copy attack, which allow an attacker to copy a watermark from one image or video frame to another one. Applications for digital watermarking include copyright protection, fingerprinting, authentication, copy control, tamper detection, and data hiding applications such as broadcast monitoring [1]. Cox et al. [2], and Hsu and Wu [3] proposed that watermark in the spatial/frequency significant region

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in image. Hartung and Girod [4] performed watermarking technique in uncompressed and compressed video sequence. Its basic principle is based on spread spectrum communications. By means of DCT transformation, the watermark can embed into MPEG-2 bit stream without increasing the bit rate. It may not decrease the computation complexity especially frequency domain. In order to improve the computation complexity and robustness for watermark embedding process, we propose a novel technique to solve it. The main properties in our scheme are blind detection which the watermark detection needs not to use the original video sequence, invisibility which the embedded watermark has not to impair the visual quality of original video, and robustness which the embedded watermark is still detected when the watermarked image encounters some modifications such as image processing, noise interference, or even deliberate attacks. Lancini et al. [5] proposed a video watermarking technique in the spatial domain; there are two main reasons for this approach that the compression algorithm strongly decreases the chrominance quality and the watermarking of the luminance direction in the spatial domain dramatically reduces the computational cost. Hence, based on these reasons, we watermark only the luminance component of each frame in the spatial domain. In this paper, a new robust algorithm for video watermark is proposed in which the watermark is embedded in uncompressed domain and can be further extracted blindly. However, for the security viewpoint, the watermark embedding usually requires the knowledge of a secret embedding key to perform. According to the characteristics of watermarking signal and video sequence, our proposed algorithm can adjust the threshold possessing the aim to change video sequence as least as possible and can get better video frame quality. Therefore, our proposed approach is extremely easy and effective; simultaneously it possesses a good compatibility with the presented video compression standards. The rest of the paper is organized as follows. In Section 2, we describe the relative background. The

embedding process and detection of watermark are described in Section 3. Section 4 presents the experiments results and a brief discussion; the conclusions are presented in Section 5.

2. Background According to a problem with pixel-based motion estimation, it must impose smoothness constraints to regularize this problem. One way of imposing smoothness constraints on the estimated motion field is to divide the image domain into the non-overlapping small regions called blocks. Assume that the motion within each block can be characterized by a simple parametric model, for example, constant, affine, or bilinear model. If the block is sufficiently small, then this model can be quite accurate. Theoretically, a block may have any polygonal shape. However, in practice, the square shape is used almost exclusively. In the simplest case, the motion in each block is assumed to be constant, that is, the entire block undergoes a translation. The detail description of block operation can be found block-matching algorithm (BMA) [6]. Some researches have embedded the watermark in motion vector of bit-stream on MPEG coding process. However, these methods cannot adjust the threshold to simultaneously obtain the good performance in the imperceptibility and robustness. Hence, owing to the BMA algorithm property, we propose a new approach based on BMA algorithm to overcome this drawback, and it can reduce the computational cost and improve the robustness performance.

3. The proposed method Due to the huge multimedia data about video data, the video images should be compressed process before storage and transmission, and more emphasizing copyright for owner of information. Hence, nowadays the watermarking embedding and detection processes are very public researches. One is embedding watermark into original images before compression. This method can get a robust watermark system. The other one is to embed watermark into compressed video data-stream. It will decrease the chrominance quality and reduce the computational cost. In MPEG system, there are three kinds of coded images in a group of pictures (GOP) which are Iframes, P-frames, and B-frames. P-frame and B-frame are a mode that codes a bi-directionally predicted frame with a normal forward-predicted frame. The Bframe temporally precedes the P-frame of the PB frame. In order to improve robust, we only use I-frames to


embed watermark in uncompressed domain. In this paper, the watermarked image is a binary image. Before embedding watermark, we first turn the binary image into binary sequence W. Then we adopt the block matching algorithm to find motion vector of each block and use the motion feature to embed watermark. Next, we will embed two bits of watermark in each embedded position. In order to effectively embed the watermark, we define each of the directions to represent the embedded bits shown in Fig. 1. There are four kinds of directions which are used to represent the combination of two bits. The bits 00, 01, 10 and 11 are denoted direction 1, 2, 3, and 4, respectively. And then we embed the watermark in video sequence periodically. For the robustness of embedded video, we embed the watermark in a short period to improve this performance. On the other hand, the visual quality of video frame will lead to rather degradation when the period is too short. Therefore, we embed into twenty frames with one watermark. In other words, our system can hide many watermarks in the different frame and effectively resists the attack. Our watermarking scheme is described as follows.

Fig. 1 Each of directions corresponding to bits representation

3.1 Embedding process We embed the watermark only the luminance component of each frame in the uncompressed domain. The original video is considered as a sequence of still images, embedding the watermark in a number of consecutive raw video frames modifies the video sequence. First, every frame is equally divided into N parts. This procedure can increase the robustness to against cropping. Next we use the BMA algorithm to get motion vector of each block of all parts respectively, and further record the minimum value of four directions of each block. Let the minimum values of four directions of each block be md1(i), md2(i), md3(i), and md4(i). We can obtain MV(i) by means of comparing four values. Here MV(i) is represented the direction of motion vector of i-th block and its value is

assigned to 1, 2, 3, or 4. Based on some experiments, we know that if the difference between the minimum value and the rest of values is too small, the watermark is extracted the failure when the watermarked video is attacked. Hence, we assign a parameter T in order to increases the difference between the minimum value and the rest of values to improve the robustness. However, the quality of watermarked video is poor when the parameter T is too large. Therefore, we let T be a threshold to trading-off with imperceptibility and robustness. Our embedding process is defined as:

MV (i ) W ( j ) & B A ! T ° ® MV (i ) W ( j ) & B A d T °MV (i) z W ( j ) ¯

match unmatch , (1) unmatch

where W(j) denotes the watermark bits represented the direction, variable A and B are the minimum value and second minimum value of (md1(i), md2(i), md3(i), md4(i)) respectively, j is a pair of bits of watermark sequence. If the bits of watermark sequence are not matched MV(i), we will modify the pixel value of block of even frames to match bits of watermark sequence. Due to our algorithm can find the best embedded position for each part to get the balance relationship between imperceptibility and robustness. Moreover, the embedded positions of each part are the difference. Finally, we can obtain an embedding key to record the embedded position. Our proposed embedding system is illustrated in Fig. 2.

3.2 Detection process The detection key equals to the embedding key. First, each frame is equally divided into N parts. And we use this detection key to find the position of the embedded watermark. Then we use the same block matching algorithm to obtain the motion direction of these blocks. Assume that the motion direction of block is 1, 2, 3, and 4 which the mean bit of watermark is denoted (00), (01), (10), and (11), respectively. After performing the detection process, we can effectively extract the corresponding embedded watermark and further to estimate the performance.

4. Experimental results and discussion In this section, we show some experimental results by means of our proposed algorithm. Here we use 480x352 raw vide sequence for the experimental format. Only the luminance component is considered in our video watermarking process. The watermark is denoted to a binary image with the size 36x20. Fig. 3 presents the watermarked video frame, raw video frame, and watermark image respectively. The search block is defined by 10x10 sizes, and the search window is set to 5. By some experimental tests, we know that B-A > 6 have better robustness. In order to let the system more robust, we set the balance threshold T is 8. A similarity measurement of the extracted and the referenced watermarks is defined as m

n

¦¦ w(i, j )wˆ (i, j ) NC

i 0 j 0 m n

,

(2)

¦¦ [w(i, j )]

2

i 0 j 0

Fig. 2 Embedding system


ˆ (i, j ) denote the original where w(i, j ) and w watermark and the extracted watermark corresponding to the i and j spatial coordinates, respectively. m and n are denoted the width and height of watermark. In Fig. 4, it is obvious that the average value of PSNR of frames for the watermarked sequence “football” in 80 frames is about 41.42 dB while the watermark keeps invisible. Fig. 5 presents the relationship between the NC values with the bit-rate for compressed watermarked sequence in MPEG standard. And these NC values have 0.78 at least in the low bit-rate. It is clear that the NC value can keep up 0.75 when the bit rate increased. Fig. 6 shows the extracted watermark when the luminance of sequence is dramatically changed and shows the extracted watermark when video frames add a random noise, which is pepper and salt. From the experimental result,

it is shown that the noise may make a little damage to our system. Hence, by our experimental results, we can obtain the excellent performance between robustness and imperceptibility. Consequently, these results show that our proposed system is powerful and feasible.

(a)

(b)

Fig. 5 Result of the NC values for the different bit rate

(c) Fig. 3 (a) Original video frame, (b) watermarked video frame, and (c) watermark image (a)

(c)

(b) (d) Fig. 6 (a) Lighter PSNR=7.02dB, (b) added a noise PSNR=11.97dB, (c) and (d) the detected watermarks.

7. References Fig. 4 PSNR of video frames

5. Conclusions In order to protect the copyright of video data, we propose a robust video watermarking embedded technique based on block matching algorithm in uncompressed domain. It is extremely easy to perform and can further adjust the threshold to trading-off with imperceptibility and robustness. The results show that our approach can effectively improve the robustness for video watermarking against various attacks (such as compression and change luminance) to achieve the copyright announce.

6. Acknowledgement This work was supported in part by the National Science Council of Republic of China under Grant No. NSC94-2213-E-007-075.


[1] C. I. Podilchuk and E. J. Delp, “Digital watermarking: algorithms and applications,” IEEE Signal Processing Magazine, vol. 18, Issue 4, pp. 33-46, July 2001. [2] I. J. Cox, F. J. Kilian, and T. Shamoon, “Secure spread spectrum watermarking for multimedia,” IEEE Transactions on Image Processing, vol. 6, no. 12, Dec. 1997 [3] C. T. Hsu and J. L. Wu, “Hidden digital watermarks in images,” IEEE Transactions on Image Processing, vol. 8, Issue 1, pp. 58-68, Jan. 1999. [4] F. Hartung and B. Girod, “Watermarking of uncompressed and compressed video,” Signal Processing, vol. 26, Issue 3, pp.283-301, 1998. [5] R. Lancini, F. Mapelli, and S. Tubaro, “A robust video watermarking technique in the spatial domain,” in Proc. of the 8th IEEE Int. Symposium on Video/Image Processing and Multimedia Communications, pp. 251-256, June 16-19, 2002. [6] Y. Wang, J. Ostermann, and Y. Q. Zhang, Video processing and communication, Prentice Hall Pub., 2001.