1-D Walsh Coding With DCT Block Watermarking Technique of Colour Images Using Y Channel

In this paper a new blind technique using one dimensional Walsh coding to improve the robustness of image watermarking is presented. The proposed technique inserts the binary bits of handwritten signatures in the DCT blocks of the Y channel of the digital colour image. Watermarking algorithm which uses 1-D Walsh coding to embed mobile phone digits in images captured by the phone camera is also introduced. The 1-D Walsh coding can be applied either horizontally or vertically. The results presented here were obtained for horizontal 1-D Walsh coding. These results prove that the use of Walsh coding has improved robustness against JPEG compression.


Introduction
Recently, digital watermarking has been proposed as one solution to the problem of intellectual property protection [1]. In d igital image watermarking, copyright protection informat ion are embedded in the image in the form of a watermark. The image must not be visibly degraded by the presence of this watermark. Another main requirement of watermarking for copyright protection applications is robustness. Thus, the watermark must be resistant to unauthorized detection and decoding. In addition, the watermark must be tolerant to normal image processing techniques (e.g. co mpression), as well as to intentional attacks (attempts to destroy or remove the watermark).
In order to make the watermark detectable after some common attacks, the watermark should meet a certain requirements. The watermark should be perceptually transparent and robust. Perceptually transparent means the difference between the watermarked image and the original one should not be observable. Robustness means the watermark should be difficu lt to be removed and it should be extractable even if so me co mmon signal p rocessing operations are applied, such as filtering and JPEG compression.
Dig ital watermarking can be classified according to a number of d ifferent criteria. One such criterion is according to the insertion domain. The watermark can be inserted in either the spatial or the transformed do main. It was found that the transform domain watermarking schemes are typically much more robust to image man ipulation compared to the spatial domain schemes. Examples of transform do mains are Discrete Fourier Transform (DFT), Discrete Cosine Transform (DCT), and Discrete Wavelet Transform (DWT) [2,3,4,5,6,7]. Watermarks may also be classified as robust or fragile. Robust watermarks are those, which are difficult to remove fro m the object in which they are embedded, despite various attacks they might be subjected to. Fragile watermarks are those that are easily destroyed by any attempt to tamper with them. There are two types of watermarking techniques: first, blind techniques where the original image is not required and second, non-blind technique where the original image is required to extract the watermark informat ion. This paper proposes the use of Walsh functions to improve the robustness of digital image watermarking techniques. In the proposed algorithms: first, Walsh functions of eight sequences are used to encode the watermark before embedding it in the lu minance component (Y) of the host colour image [8]. The second algorith m will allow the watermark to be embedded many times in grey images captured by a mobile phone camera to increase the robustness against many attacks [9]. Both methods are blinds and do not require the original image to recover the watermark. The paper consists of 4 sections. In section 2, Walsh coding functions are introduced and also the DCT watermarking technique using the low frequency components is presented. Results, discussion and comparison with other algorith ms are presented in Section 3. Finally, section 4 contains the concluding remarks.

Walsh Codi ng of Signature
Walsh coding is used in this method to increase the robustness of the digital watermark. Walsh functions are orthogonal and contain length elements. The Walsh function is produced proportional to the value of the length elements, where this length is in terms of 2 n with n as an integer. In the proposed method, the 1-D Walsh function is used to encode the signature before being embedded in the host image. The 1-D Walsh coding can be applied either horizontally or vertically. The proposed technique is carried out using the horizontal 1-D Walsh coding. By utilizing this type of coding, each bit of the signature's vectors will be replaced by the Walsh code sequence. This process is carried on all signatures' pixels. This involves man ipulations with Hadamard matrices as detailed in [10,11]. An example of Walsh functions with length=8 is: In the proposed technique, the 16x64 signature is repeated and shuffled four t imes to become 64x64 b inary bits. Then Walsh length of eight is used to replace each bit of the signature's row. The resulted Walsh coded signature would have 64x256 bits of values: +1 and -1 only. The effect of applying the Walsh coding to the signature is to spread it horizontally. The actual pixel values of the signature change fro m binary[0, 1] to integer values in the range[-1, +1]. Figure 1 shows the effect of applying the shuffling process to the signature.

Original Signature
Shuffled Signature

DCT Blocks Algorithm Techni que
The proposed algorithm scheme is based on feeding watermark bits into the low frequency band of the cover image DCT using 8x8 b locks. The eight lo w-frequency coefficients excluding the dc co mponent of the 8x8 DCT blocks are used to hide the watermark b its [12,13]. In the embedding, first, the signature is 1-D Walsh encoded and then the encoded signature's elements are inserted into the DCT blocks coefficients of the host image. The embedding process is achieved by placing the Walsh encoded signature's bits (either +1 o r -1) into the stated (odd or even) coefficient value of the b lock and then taking the inverse DCT and constructing the watermarked image. The scale factor is an absolute integer number which is mu ltip lied by the embedded data bit to improve the robustness. After doing the block then it is transformed back to the spatial domain as shown in Figure 2.
The decoding process is achieved as follows, first is to convert the watermarked image into (8x8) blocks and applying the DCT to each block. Then Walsh coded coefficients are located for even or odd values. Then the signature is obtained by 1D Walsh decoding.

Walsh Codi ng of Mobile Phone Number
The new watermarking scheme has also been implemented to hide mobile phone numbers in the host images. The reasons for choosing the phone numbers because each individual has a unique nu mber (including the international code) which can be used to watermark h is/her own images. For examp le the 14 digits of the UA E mob ile phone number including the international country code (00971 50 3658212) can be used for this purpose. Also, the summation of the decimal digits is added to the 14 digits to make them 16 decimal dig its (00971 50 3658212 49). The advantage of adding the summat ion to the 14 digits is to be able to check that the extracted nu mber is correct o r not. Each of the 16 decimal digits is converted into 4 bit binary number and Walsh coded. The size of the watermark is small co mpared to the host image so it can be embedded many times [9].
One dimensional Walsh functions are used to encode the phone digits before embedding them in the cover image. This algorith m was carried out using the horizontal 1-D Walsh coding. To implement this type of coding, each row's vector of the binary numbers will be rep laced by its relevant Walsh code and then added to the DCT components. The method is imp lemented by swapping the binary representation of the 16 digits with the above Walsh codes (W1, W2, W3 and W4). The resulted Walsh coded phone numbers would have 64x64 b its of values: +1 and -1. Figure 2 shows the effect of applying 1D Walsh coding on the phone number with 4 Walsh sequence length. In this technique Walsh functions with length=4 are used: (2) In order to verify the robustness and functionality of the first algorith m, a nu mber of 24-bit colour images with 512x512 pixels have been used to test the proposed algorith ms. Also a 16x64 binary signature image has been used as a watermark. Figure 3 shows samples of some images that have been used as host images in the watermarking algorith m. It is clear that the distortion caused by the new watermarking scheme is invisible. The test also, covered the use of different scaling factors for the watermarking and their effect on the fidelity of the watermarked image. Investigation is carried out to assess the fidelity of the images by using the Peak Signal to Noise Ratio (PSNR) and the Mean Structural Similarity (SSIM) [14]. Table1 shows the PSNR and SSIM values of different images using DCT b locks with Walsh coding. Table 2 shows the values of the JPEG quality below which the watermark cannot be extracted. It is clear that increasing of the scaling factor enhances the robustness of the algorith m at the expense of increasing the distortion caused to the watermarked images. Table 3 shows the different attacks using the Stir mark software. The algorithm survived JPEG and some other attacks.

Results and Discussion
In this section, the robustness of the second algorithm using mobile phone number as a watermark has been tested and compared with the case without using Walsh sequences. The analysis covered the use of different scaling factors for the watermarking and their effect on the fidelity of the watermarked image. Figure 4 shows samples of so me images that have been used as host images in the watermarking algorith m. It is clear that the distortion caused by the new watermarking scheme is invisib le.  The fidelity of the images is assessed by using the Peak Signal to No ise Ratio (PSNR) and the Mean Structural Similarity (SSIM) [14]. It is clear that the algorithm is mo re robust with Walsh coding.     Table 4 shows the PSNR and SSIM values of different images using DCT algorithm with Walsh coding. Table 5 shows the extracted phone number under different values of JPEG attack and using different values of scaling factors, respectively. It is clear that increasing of the scaling factor enhances the robustness of the algorith m at the expense of increasing the distortion caused to the watermarked images.
The algorith m is also tested using Stir mark attacks by using Lena image with scaling factor 14. Tab le 6 shows the Stir mark attacks and their normalised correlation (NC) values. The algorith m survived JPEG and some other attacks. It should be noted that the phone number is either recovered or not and therefore the NC is either 1 or 0.

Conclusions
In this paper, a new technique to embed 1-D Walsh coded handwritten signatures and mobile phone number as a watermark into grey level and colour images is presented. The proposed method used a block DCT based algorithm. It was found that the use of 1-D Walsh coding with DCT blocks provides high robustness against JPEG attacks compared to the method of embedding without coding. It was also found that the use of scaling factor with Walsh coding improves the robustness against JPEG co mpression but at the expense of degrading the quality of the watermarked image. The new scheme is blind and the watermark can be ext racted without the original image.