Song Guoxiang

Three Novel Models of Threshold Estimator for Wavelet Coefficients

The soft-thresholding and the hard-thresholding method to estimate wavelet coefficients in wavelet threshold denoising are firstly discussed. To avoid the discontinuity in the hard-thresholding and biased estimation in the soft-thresholding, three novel models of threshold estimator are presented, which are polynomial interpolating thresholding method, compromising method of hard- and soft-thresholding and modulus square thresholding method respectively. They all overcome the disadvantages of the hard- and soft-thresholding method. Finally, an example is given and the experimental results show that the improved techniques presented in this paper are efficient.

Nonlinear calibration and data processing of the solar radio burst

The processes of the sudden energy release and energy transfer, and particle accelerations are the most challenge fundamental problems in solar physics as well as in astrophysics. Nowadays, there has been no direct measurement of the plasma parameters and magnetic fields at the coronal energy release site. Under the certain hypothesis of radiation mechanism and transmission process, radio measurement is almost the only method to diagnose coronal magnetic field. The broadband dynamic solar radio spectrometer that has been finished recently in China has higher time and frequency resolutions. Thus it plays an important role during the research of the 23rd solar cycle in China. Sometimes when there were very large bursts, the spectrometer will be overflowed. It needs to take some special process to discriminate the instrument and interference effects from solar burst signals. According to the characteristic of the solar radio broadband dynamic spectrometer, we developed a nonlinear calibration method to deal with the overflow of instrument, and introduced channel-modification method to deal with images. Finally the interference is eliminated with the help of the wavelet method. Here we take the analysis of the well-known solar-terrestrial event on July 14th, 2000 as the example. It shows the feasibility and validity of the method mentioned above. These methods can also be applied to other issues.

Image-Feature Based Second Generation Watermarking in Wavelet Domain

An image-feature based second generation watermarking scheme is proposed in this paper. A host image is firstly transformed into wavelet coefficients and features are extracted from the lowest approximation. Then a watermark sequence is inserted in all high frequency coefficients corresponding to the extracted featured approximation coefficients. Original host image is not needed in watermarking detection, but the featured approximation coefficients position is necessary for robust detection. The correlation between the embedded watermark and all high frequency coefficients of a possibly corrupted watermarked image corresponding to the approximate coefficients at the same position as the original featured approximation coefficients is calculated and compared to a predefined threshold to see if the watermark is present. Experimental results show the watermark is very robust to common image processing, lossy compression in particular.An image-feature based second generation watermarking scheme is proposed in this paper. A host image is firstly transformed into wavelet coefficients and features are extracted from the lowest approximation. Then a watermark sequence is inserted in all high frequency coefficients corresponding to the extracted featured approximation coefficients. Original host image is not needed in watermarking detection, but the featured approximation coefficients position is necessary for robust detection. The correlation between the embedded watermark and all high frequency coefficients of a possibly corrupted watermarked image corresponding to the approximate coefficients at the same position as the original featured approximation coefficients is calculated and compared to a predefined threshold to see if the watermark is present. Experimental results show the watermark is very robust to common image processing, lossy compression in particular.

Nonlinear approximation of image based on monoscale orthonormal ridgelets frame

Abstract A new tight frame called as monoscale orthonormal ridgelet frame (MORF) is proposed. The localization principle and the orthonormal ridgelet constructed by Donoho are applied to construct the MORF, which are used to evaluate the order of nonlinear approximation for image with edge. Because the new tight frame not only has directionality but also bears orthonormality. It overcomes redundancy of Candess monoscale ridgelets and provides many excellent properties in practical application. Theoretical analysis and experiments demonstrate that the new frame has remarkable potential for image compression, image reconstruction, and image denoising with the simple refinement for MORF.