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Adaptive shrinkage on dual-tree complex wavelet transform for denoising real-time MR images

Venuji Renuka Simi, Reddy Edla Damodar

Biocybernetics and Biomedical Engineering

2019

Vol. 39, no. 1

133--147

Performance of denoising filters which are based on the principle of wavelet thresholding greatly depends upon selection of the threshold value. An objective method is proposed in this paper for computing the optimum value of threshold in DTCWT based denoising. At optimum threshold, annoying intensity transitions of pixels in the homogeneous regions of the images, contributed by noise get completely suppressed and the true edges remain unaffected. For finding optimum value of threshold a newly derived quality metric termed as Optimum Denoising Index (ODI), which quantifies both the edge-preservation and smoothing of homogeneous regions is used. The ODI values corresponding to mean, median, Gaussian, Wiener, Bilateral, Kuwahara filters and wavelet thresholding are 0.1192±0.0118, 0.2196±0.0125, 0.1283±0.0118, 0.2106±0.0145, 0.1590±0.0331, 0.2200±0.0101 and 0.2516±0.0094, respectively. The wavelet thresholding has better edge-preservation and denoising capacity than the said denoising schemes. The ODI is highly correlated with its existing alternatives like Peak Signal to Noise Ratio (PSNR) and Structured Similarity Index Metric (SSIM) with values 0.9165 0.0536 and 0.9050 0.0452 respectively. This shows ODI is a good alternative to PSNR and SSIM.

Image denoising using new wavelet thresholding function

Dehda B., Melkemi K.

Journal of Applied Mathematics and Computational Mechanics

2017

Vol. 16, nr 2

55--65

In this paper, we propose a new image denoising method based on wavelet thresholding. In this method, we introduce a new nonlinear thresholding function characterized by a shape parameter and basic properties. These characteristics make the new method able to achieve a compromise between both traditional thresholding techniques such as Hard and Soft thresholding. The experimental results show that our proposed method provides better performance compared to many classical thresholding methods in terms of the visual quality of the denoised image.

Denoising methods for improving automatic segmentation in OCT images of human eye

Stankiewicz A., Marciniak T., Dąbrowski A., Stopa M., Rakowicz P., Marciniak E.

Bulletin of the Polish Academy of Sciences. Technical Sciences

2017

Vol. 65, nr 1

71--78

This paper presents analysis of selected noise reduction methods used in optical coherence tomography (OCT) retina images (the socalled B-scans). The tested algorithms include median and averaging filtering, anisotropic diffusion, soft wavelet thresholding, and multiframe wavelet thresholding. Precision of the denoising process was evaluated based on the results of automated retina layers segmentation, since this stage (vital for ophthalmic diagnosis) is strongly dependent on the image quality. Experiments were conducted with a set of 3D low quality scans obtained from 10 healthy patients and 10 patients with vitreoretinal pathologies. Influence of each method on the automatic image segmentation for both groups of patients is thoroughly described. Manual annotations of investigated retina layers provided by ophthalmology experts served as reference data for evaluation of the segmentation algorithm.