to set, e.g., AC to 5% and DC to 50% and both suppressions will be applied to the image simultaneously.Įxplanation of details of the wavelet transform and parameters mentioned can be found in the text below. However, it is possible to combine settings of both coefficients together, i.e. only Approximation Coefficients can be suppressed (0-100%) or only Detailed Coefficients (0-100%). Here the plugin suppresses coefficients separately, i.e. Soft thresholding generally gives a smoother image. It can also be selected to do either Soft Thresholding or Hard Thresholding. It is accomplished using VisuShrink thresholding method and the user defines the threshold by selecting the level of denoising (that equals Sigma value of the Universal threshold Sigma takes values 1-128) in the dialog. Hard Thresholding – hard VisuShrink thresholding: These two tools demonstrate another use of wavelet transform for image denoising/filtering.Soft Thresholding – soft VisuShrink thresholding.Here, both Approximation and Detailed Coefficients are taken together as a one set when doing suppression. User can set the level of suppression that equals the percentage of the coefficients to be removed (i.e., 0% means no values are suppressed, 100% means all the values are suppressed).
coefficients are ranked according to absolute value of their amplitude. (AC & DC) – suppresses some amount of the smallest coefficients, i.e. Wavelet Filter – wavelet family and a kind of the applied filter (Haar 1, Daubechies 1-20, Symlets 2-20, Coiflets 1-5, Biorthogonal 1.1-6.8, Reverse Biorthogonal 1.1-6.8, Discrete Meyer 1). Level of Details – number of levels of decomposition of images. Refresh button – returns all items in the dialog to default values. This is due to the proper computation of levels of wavelet decomposition of images, see below.ĭescription of functionality of items in the plugin window
We should mention here that sizes of input image matrices must be of power of 2, common sizes are: 64, 128, 256, 512, 1024, 2048 etc., otherwise the plugin will not start and a warning message appears again. Applying Synchronize All in the Sync Wins dialog is helpful when navigating through image stacks.
The third and fourth pictures appear only after checking corresponding boxes in the main dialog. The first picture is the input image, the second one is the filtered picture (“Filtered-” prefix), the third one contains the wavelet coefficients (“WT-“ prefix), that are converted to 8-bit and are intensity scaled for good visualization, the fourth picture (“WT-NoStretch-” prefix) contains float values of the wavelet coefficients without intensity scaling. When starting the plugin, pictures and Sync Wins dialog appear, like in the picture above, together with the plugin dialog. Plugin for wavelet-based denoising/filtering image data
0 kommentar(er)
