158 CHAPTER 7 CONCLUSION AND FUTURE WORK The aim of this thesis was to present robust watermarking techniques for medical image. Section 7.1, consolidates the contributions made by the researcher and Section 7.2 points up the directions in which future research studies can be focused. 7.1 CONCLUSION In this thesis, the discrete wavelet transform based on quantization level, pseudo noise sequence, lifting scheme and checkerboard method of four different efficient robust watermarking algorithms have been proposed and analyzed to protect the copyright regulations of digital medical images with watermark embedding and watermark extraction process. In addition, the advanced discrete wavelet transform based quantization techniques of watermarking (ADQW) algorithm has been delineated. The ADQW algorithm has frequency domain to preserve the history of medical image by embedding the medical diagnosis report. The scheme allows the simultaneous storage and transmission of electronic patient record along with image authentication information which can be extracted at the receiving end without the original image. Encryption of the embedded data is done to provide additional security. In the ADQW method, JPEG compression attacks for all compression ratios (0 to 100) are constant and there is a 14% of improvement
159 in the PSNR value when compared with Lin et al (2010) algorithm. Similarly for Gaussian filtering attacks of all sizes of window (1-10), it is constant and 21% of increase in the PSNR value is obtained when compared with Lin et al (2010) algorithm. The adding Gaussian noise, salt and pepper noise attacks for all noise densities (0 to 1) remain constant, 18% and a 11% larger NC value is obtained when compared with Lin et al (2010) algorithm. It also provides sufficient capacity for storing more than half of kilobytes of patient data for the images of size 256 x 256. There fore the ADQW algorithm can easily be used in e-diagnosis of medical applications. Next, an improved discrete wavelet transform based PN sequence for watermarking (IDPW) algorithm has been discussed. The IDPW algorithm has incorporates telemedicine applications by watermarking radiological images with sensitive medical information in binary image format. Medical information such as telemedicine origin centre of doctor s signature (watermark) is embedded into the input CT scan image as watermarks. These watermarks are in binary image formats which add robustness by allowing the recovery of the watermarks even at a low correlation between the original and extracted watermarks. In the IDPW algorithm, both the Gaussian and average filtering attacks for all sizes of window 1to10, the Peak Signal-Noise Ratio value is constant and shows a 22% improvement when compared with both Kung et al (2009) and Lin et al (2010) algorithms. Similarly, adding Gaussian noise attacks for all noise densities 0 to 1, the PSNR value is constant and achieves a 22% improvement when compared with Lin et al (2010) algorithm. Also the SPIHT compression attacks for all the compression ratios 0 to 100 the Normalized Correlation value is constant and reaches a 10% increase when compared with Lin et al (2010) algorithm. Similarly, in salt and
160 pepper noise attacks for all noise densities 0 to1, the Normalized Correlation value is constant and rises 6% higher when compared with Lin et al (2010) algorithm. The embedding as well as extraction phases are performed in wavelet domain and the proposed approach is highly secure and robust to all sorts of watermarking attacks. The robustness of the IDPW algorithm is good enough for all types of attacks. Hence the IDPW algorithm is suitable for copyright protection, potential applications in military, medical and law enforcement related image processing. A novel DWT based lifting scheme of watermarking (NDLW) algorithm has been provided. The NDLW algorithm makes use of human visual system for protecting the copyright guidelines of medical images. The watermarking has been performed in wavelet domain with the aid of bi-orthogonal wavelet transform with lifting scheme. The incorporation of HVS model into the proposed scheme has enabled the creation of an efficient watermarking scheme for effective copyright protection of images. In the NDLW algorithm, the SPIHT compression attacks for all compression ratios from 0 to 100, the Peak Signal-Noise Ratio value is 44.64dB where the value is constant with 11% improvement when compared with Lin et al (2010) algorithm. Similarly, for the average filtering attacks of all sizes of window from 1 to 10, the constant PSNR value is 41dB and shows a 6% increase when compared with Liu et al (2006) algorithm. Also the salt and pepper noise attacks for all noise density from 0 to 1, the PSNR value is 53dB which is constant and with 16% improvement when compared with Ye and Tan (2008) algorithm.
161 In the NDLW algorithm, the JPEG compression attacks for all compression ratios range from 0 to 100 where the Normalized Correlation value 0.98 is high and shows a 20% improvement when compared with Liu et al (2006) algorithm. Similarly, in the Gaussian filtering attacks for all sizes of window from 1 to 10, the Normalized Correlation value is 0.68 which is constant and shows a 19% increase when compared with Lin et al (2010) algorithm. Also the salt and pepper noise attacks for all noise density from 0 to 1, the Normalized Correlation value 0.98 is constant and shows a 6% rise when compared with Kung et al (2009) algorithm. The NDLW method provides better tradeoff between capacity and imperceptibility of a watermarking system compared to the existing schemes. This NDLW algorithm has met both the requirements for effective copyright protection scheme as well as imperceptibility and robustness. Further, experiments have been performed by embedding the medical diagnosis reports of patients in medical images to show the potential of one proposed scheme for application in health care systems. The thesis dealt with a modified DWT based checkerboard method of watermarking (MDCW) algorithm. The efficient image watermarking technique is presented to protect the copyright protection of digital images with watermark embedding and watermark extraction. In the embedding process, the DWT is used to decompose the input medical image. The grayscale digital signature image is used as a watermark and it is embedded in the HL and LH sub-bands of the wavelet transformed image with the aid of the embedding process. Subsequently, the embedded watermark is restored back to its original position and the watermarked image is attained by using inverse discrete wavelet transform. In the extraction process, the recovery of
162 the watermark image is achieved with the aid of the proposed extraction technique. In the MDCW algorithm, the SPIHT compression attacks for all compression ratios ranging from 0 to 100, the Peak Signal-Noise Ratio value is 44dB which is constant and shows a 2% rise when compared with Lin et al (2010) algorithm. Similarly, the Gaussian filtering attacks for all sizes of window from 1 to 10, the PSNR value is 45dB high and shows a 24% improvement when compared with Ye and Tan (2008) algorithm. Also the salt and pepper noise attacks for all noise density from 0 to 1, the PSNR value is above 50dB when compared with Ye and Tan (2008) algorithm. In the MDCW algorithm, the SPIHT compression attacks for all compression ratios from 0 to 100, the normalized correlation value is 0.96 where the value is constant and shows a 20% improvement when compared with Liu et al (2006) algorithm. Similarly, for both Gaussian and salt and pepper noise attacks of all noise density from 0 to 1, the normalized correlation value 0.98 is constant and shows a 6% increase when compared with Lin et al (2010) algorithm. The results obtained from the experimentation establish that the proposed watermarking techniques provide better results with higher accuracy. Also, the results are compared with the four proposed ADQW, IDPW, NDLW and MDCW algorithms by means of compression standards, filtering techniques and noise types. The proposed scheme allows the simultaneous storage and transmission of electronic patient record which can be extracted at the receiving end without de- grading the original image. The scheme can easily be used in e-diagnosis applications such as tele-consulting, tele-surgery and tele-diagnosis.
163 7.2 FUTURE WORK The research study discussed in this thesis indicates many new directions for researchers to pursue further research in this domain. Some of the are avenues to be explained are summarized below: 1. Robust watermarking techniques for Region Of Interest (ROI) based image and video coding can provide the right balance between imperceptibility and robustness. A visual attention model based watermarking technique can be a possible way to achieve the same. 2. There is an imperative need to explore watermarking based authentication applications in JPEG 2000 streaming, e.g. controlled distribution of copyrighted images to mobile, portable devices, computer etc. 3. It is necessary to develop real time watermarking based authentication scheme using bit stream domain watermarking for H.264/SVC etc. Such schemes are useful in multimedia content distribution including user authentication for pay-tv. 4. Future studies must promote joint compression domain scalable watermarking based image and video coding schemes that offers scalability in media distribution while resolving Digital Right Management (DRM) issues. 5. The possibilities of using the Peano-Hilbert scan for the AW-TDR watermarking technique can be explored further to find the optimal recovery point. 6. As compression is acceptable in a medical standard such as DICOM, investigation on embedding in other domains such as
164 DCT (used in JPEG) and wavelet (used in JPEG2000) should be considered to make sure that the watermark is robust against those compression schemes. 7. Application on other image modalities such as Positron Emission Tomography (PET), Single Photon Emission Computerized Tomography (SPECT), Nuclear Medicine (NM), Digital Subtraction Angiography (DSA), and Digital- Fluorography (DF), Colored medical image TEP require scrutiny. 8. Issues in practical application in a real-world hospital environment need to be investigated before watermarking could possibly be used.