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In medical images, noise suppression is a particularly delicate and difficult task. A tradeoff between noise reduction and the preservation of actual image features has to be made in a way that enhances the diagnostically relevant image content. The method of wavelet thresholding has been used extensively for denoising medical images. The idea is to transform the data into the wavelet basis, in which the large coefficients are mainly the signal and the smaller ones represent the noise. By suitably modifying these coefficients, the noise can be removed from the data. In this paper, we evaluate several two-dimensional denoising procedures using medical test images corrupted with additive Gaussian noise. Our results, using the peak-signal-to-noise ratio as a measure of the quality of denoising, show that the NormalShrink method outperforms the other wavelet-based techniques (VisuShrink, BayesShrink). We also demonstrate that garrote shrinkage offers advantages over both hard and soft shrinkage.

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Currently, researchers are orienting their effort to selective encryption in order to protect video sequences against attacks during their transmission over a public channel. The reasons for this trend are of great importance. To reduce video data amount, the video compression chain is essential and to ensure their security, while in transmission, an encryption algorithm is evident. Thus, inserting the encryption module in the video compression chain is better than applying compression and encryption separately in terms of computing time. This paper presents a chaos based encryption method inserted in the H.264 Advanced Video Coding (AVC) used for video conferencing applications. The selective encryption was applied on context adaptive variable length coding (CAVLC) and on the signs of motion vectors. The results were deducted according to the values of peak signal to noise ratio (PSNR), structural similarity (SSIM) and the encryption rate (ER). Combining selective encryption of CAVLC (SE-CAVLC) and motion vector sign encryption (MVSE) are interesting in terms of enhancing the encryption and to damage the visual quality of the decoded video for both Intra and Inter predicted frames.