Wavelet thresholding is an important branch of the image denoising field. A key parameter in
the algorithms is noise level. As a novel tool of image analysis, quaternion wavelet owns
some superior properties compared to discrete wavelets, such as nearly shift-invariant
wavelet coefficients and phase based texture presentation. We aim to propose an easy and
efficient method to estimate the noise level accurately via quaternion wavelet and further
improve the denoising performance. We find that the variance sum of high frequency …