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Magnetic Resonance Imaging Physical Principles And Sequence Design

In this paper, we present a medical image integrity verification system to detect and approximate local malevolent image alterations (e.g., removal or addition of lesions) as well as identifying the nature of a global processing an image may have undergone (e.g., lossy compression, filtering, etc.). The proposed integrity analysis process is based on nonsignificant region watermarking with signatures extracted from different pixel blocks of interest, which are compared with the recomputed ones at the verification stage. A set of three signatures is proposed. The first two devoted to detection and modification location are cryptographic hashes and checksums, while the last one is issued from the image moment theory. In this paper, we first show how geometric moments can be used to approximate any local modification by its nearest generalized 2-D Gaussian. We then demonstrate how ratios between original and recomputed geometric moments can be used as image features in a classifier-based strategy in order to determine the nature of a global image processing. Experimental results considering both local and global modifications in MRI and retina images illustrate the overall performances of our approach. With a pixel block signature of about 200 bit long, it is possible to detect, to roughly localize, and to get an idea about the image tamper.

A Watermarking-Based Medical Image Integrity Control System and an Image Moment Signature for Tampering Characterization

Due to the advancement in Computer technology and readily available tools, it is very easy for the unknown users to produce illegal copies of multimedia data which are floating across the Internet. In order to protect those multimedia data on the Internet many techniques are available including various encryption techniques, steganography techniques, watermarking techniques and information hiding techniques. Digital watermarking is a technique in which a piece of digital information is embedded into an image and extracted later for ownership verification. Secret digital data can be embedded either in spatial domain or in frequency domain of the cover data. In this paper, a new singular value decomposition (SVD) and discrete wavelet transformation (DWT) based technique is proposed for hiding watermark in full frequency band of color images (DSFW). The quality of the watermarked image and extracted watermark is measured using peak signal to noise ratio (PSNR) and normalized correlation (NC) respectively. It is observed that the quality of the watermarked image is maintained with the value of 36dB. Robustness of proposed algorithm is tested for various attacks including salt and pepper noise and Gaussian noise, cropping and JPEG compression.

DWT-SVD Combined Full Band Robust Watermarking Technique for Color Images in YUV Color Space

Multimedia technology usages is increasing day by day and to provide authorized data and protecting the secret information from unauthorized use is highly difficult and involves a complex process. By using the watermarking technique, only authorized user can use the data. Digital watermarking is a widely used technology for the protection of digital data. Digital watermarking deals with the embedding of secret data into actual information. Digital watermarking techniques are classified into three major categories, and they were based on domain, type of document (text, image, music or video) and human perception. Performance of the watermarked images is analysed using Peak signal to noise ratio, mean square error and bit error rate. Watermarking of images has been researched profoundly for its specialized and modern achievability in all media applications such as copyrights protection, medical reports (MRI scan and X-ray), annotation and privacy control. This paper reviews the watermarking technique and its merits and demerits.

Digital watermarking techniques for image security: a review

A robust image watermarking scheme in which a binary image is embedded in the singular values of selected DWT blocks in the horizontal and vertical sub-bands of a 1-level decomposition of a gray-scale image is proposed. The embedded blocks are selected by a secret key to enhance imperceptibility. A watermarked image that is perceptually indistinguishable from the original is obtained. The watermarking retrieval is non-blind and requires the use of parameters extracted during the watermarking process. The performance of the proposed algorithm is tested by comparing the retrieved watermark to the original watermark. Computer simulation results show that the algorithm is robust to common signal processing attacks such as Gaussian noise, cropping, and low pass filtering. It is also resistant to JPEG compression.

An image watermarking method based on the singular value decomposition and the wavelet transform

This paper proposes a novel enhancement algorithm for degraded binary document images captured using a low end cell phone camera. The algorithm starts with colour to grey scale conversion followed by contrast stretching. Then single scale retinex enhancement is performed to increase the contrast, reduce global variance and improve the background uniformity of the image. Otsu's binarisation method is then used to dichotomize the image and finally, morphological dilation is performed to preserve stroke connectivity of the document characters by bridging any gaps resulting from the thresholding process. Computer simulation experiments have been used to demonstrate the effectiveness of the proposed algorithm. The results show a significant improvement over the Otsu's method in terms shadow removal, document legibility and optical character recognition. The results also compare well with the state of the art Sauvola's method results.

An improved enhancement of degraded binary text document images using morphological and single scale retinex operations

A digital image watermarking scheme that uses invariant centroids to detect and correct geometric attacks is proposed. The centroids are determined by computing a convergent geometric moment of a circular region of a predetermined size. These centroids serve as reference points for a region of interest in which a binary image is embedded using a wavelet based method and a private key to enhance robustness. In the watermark retrieval phase, the geometric attacks are estimated by identifying the centroids shift and making corrections. The centroids also help to identify the likely region in which the watermark could have been embedded. A search is performed by slightly perturbing the region of interest boundary until the highest correlation of the extracted watermark to the original watermark is obtained. Computer simulation results show that the method is effective in the retrieval of watermarks after geometric attacks. It is also robust against common signal processing attacks.

A Geometric Attack Resistant Image Watermarking Scheme Based on Invariant Centroids

Single image super resolution requires approximation of high frequency information that was not captured in the available low resolution image. The process may result in an image that differs significantly from the original scene if no constraints are imposed. Iterative back-projection is one method used to guide the resolution enhancement process. This paper augments the iterative back-projection with edge sharpening of the error image and guided filtering to improve the high frequency content of the image. The algorithm is tested on 27 RGB colour images including the 24 images from the Kodak lossless true colour image set. The results are compared to those obtained using bicubic interpolation, wavelet zero padding and the established edge guided method. In the average results from the 27 images, the proposed method is observed to have an improvement of 0.9% over bicubic interpolation, 5.8% over wavelet zero padding and 7.5% over new edge directed Interpolation in terms of peak signal to noise ratio. The corresponding improvement in terms of structural similarity index are 1.1%, 3% and 6.8% respectively. In addition, the proposed method has the effect of suppressing spurious colours in the enhanced image.

Single image super resolution with guided back-projection and LoG sharpening

A comparative analysis to determine the most effective video watermarking algorithm between SVD/DWT hybrid and Singular Value Decomposition (SVD) is reported in this paper. Blind video watermarking schemes are simulated and attempts made to recover the watermark after some signal processing attacks such as median filtering and Histogram equalization. The quality of the extracted watermark was then measured using the SSIM index. From the computer simulation results using a diverse set of standard video clips the SVD/DWT hybrid performed better than the reference. An average value of the SSIM index of 0.98 was obtained. The SVD transform values varied from 0.57 to 0.78 for histogram equalization attacks and 0.83 to 0.9 for median filtering attacks. The results reveal the superiority of the SVD/DWT hybrid technique over SVD for digital rights enforcement.

Elijah Mwangi

Papers

An image watermarking method based on the singular value decomposition and the wavelet transform

An improved enhancement of degraded binary text document images using morphological and single scale retinex operations

A Geometric Attack Resistant Image Watermarking Scheme Based on Invariant Centroids

Single image super resolution with guided back-projection and LoG sharpening

A robust video watermarking approach based on a hybrid SVD/DWT technique