During acquisition, the SONAR images are corrupted by multiplicative noise (speckle).The aim of an image denoising
algorithm is then to reduce the noise level, while preserving the image features. There is a great diversity of wavelet
based estimators used like denoising systems. The corresponding denoising methods have three steps: the computation of
the forward Wavelet Transform (WT); the filtering of the wavelet coefficients; and the computation of the inverse
wavelet transform of the result obtained. In the following, the Dual Tree Complex Wavelet Transform (DT-CWT) will
be associated with a variant of a maximum a posteriori bishrink filter because its explicit input-output relation permits a
sensitivity analysis. The bishrink filter has a high sensitivity with some parameters, especially in the homogeneous
regions. The main idea of this paper is to reduce this sensitivity by diversification. In this respect the regions with
different homogeneity degrees are identified and in each of them the WT of the acquired image is filtered using a number
of different variants of bishrink filters in accordance with its homogeneity.
Watermarking using pixel-wise masking in the wavelet domain proves to be quite robust against common signal
processing attacks. Initially, in a system proposed by Barni et al., embedding is made only in the highest resolution level;
there are two disadvantages to this technique: the watermark information can be easily erased by a potential attacker and
embedding in the DWT is susceptible to geometric attacks, such as shifting. To enhance this watermarking method, we
use a modified perceptual mask that models the human visual system behavior in a better way, previously proposed by
the authors. The texture content is appreciated with the local standard deviation of the original image, which is further
compressed in the wavelet domain. Since the approximation image of the coarsest level contains too little information,
we appreciate the luminance content using a higher resolution level approximation sub-image. To increase the capacity
of the watermarking scheme the embedding is made in the HWT domain, using two strategies: in the real parts of the
HWT coefficients and in the absolute value of the HWT coefficients of the original image. The implementation of the
HWT is made using a new technique, recently proposed by the authors. Moreover, we make use of all the levels except
the coarsest one, for attack resilience. We use three types of detectors that take advantage of the hierarchical
decomposition. Tests were made for different attacks (JPEG compression, median filtering, resizing, cropping, gamma
correction, blurring, shifting and addition of white Gaussian noise), that prove the effectiveness of perceptual
watermarking in the HWT domain.
The aim of this paper is to present a new method for the estimation of the instantaneous frequency of a frequency modulated signal, corrupted by additive noise. Any time-frequency representation of an acquired signal is concentrated around the instantaneous frequency law of its useful component (the projection of the ridges of the time-frequency representation on the time-frequency plane) and realizes the diffusion of its noise component. So, extracting the ridges of the time-frequency representation, the instantaneous frequency of its useful component can be estimated. In this paper a new time-frequency representation is proposed. Using the image of this new time-frequency representation, its ridges can be extracted with the aid of some mathematical morphology operators. This is a ridges detection mechanism producing the projection on the time-frequency plane. This projection represents the result of the proposed estimation method. Some simulations prove the qualities of this method.
The aim of this paper is to present a new method for the estimation of the instantaneous frequency of a frequency modulated signal, corrupted by additive noise. This method represents an example of fusion of two theories: the time-frequency representations and the mathematical morphology. Any time-frequency representation of a useful signal is concentrated around its instantaneous frequency law and realizes the diffusion of the noise that perturbs the useful signal in the time - frequency plane. In this paper a new time-frequency representation, useful for the estimation of the instantaneous frequency, is proposed. This time-frequency representation is the product of two others time-frequency representations: the Wigner - Ville time-frequency representation and a new one obtained by filtering with a hard thresholding filter the Gabor representation of the signal to be processed. Using the image of this new time-frequency representation the instantaneous frequency of the useful signal can be extracted with the aid of some mathematical morphology operators: the conversion in binary form, the dilation and the skeleton. The simulations of the proposed method have proved its qualities. It is better than other estimation methods, like those based on the use of adaptive notch filters.