Filters (Spatial): Nonlinear Noise Reduction and Filters (Spatial): Nonmaximum Suppression: Difference between pages

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== Background ==
This algorithm defines the edges of an image by calculating the nonmaximum suppression of an image at a user-defined scale. An ''edge'' is defined as the union of points for which the gradient magnitude assumes a maximum in the gradient direction.
This algorithm provides a port of the SUSAN (Smallest Univalue Segment Assimilating Nucleus) low-level image processing program.


For information about SUSAN, see <u>http://www.fmrib.ox.ac.uk/~steve</u>.
{| width="90%" border="1" frame="hsides" frame="hsides"
 
SUSAN noise reduction uses nonlinear filtering to reduce noise in an image while preserving both the underlying structure and the edges and corners. It does this by averaging a voxel only with local voxels that have similar intensity.
 
Table 1 explains the possible responses that the SUSAN filter provides if it cannot determine the neighborhood and based on whether you selected the option of using the median.
 
<div>
 
{| border="1" cellpadding="5"
|+ <div>'''Table 1. Possible responses of the SUSAN filter''' </div>
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<div>'''Use median'''  </div>
[[Image:noteicon.gif]]
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<div>'''SUSAN area''' </div>
[http://mipav.cit.nih.gov/documentation/HTML Algorithms/FiltersSpatialNonmaximumSuppression.html For more information about the algorithm, refer to the MIPAV web site: {http://mipav.cit.nih.gov/documentation/HTML Algorithms/FiltersSpatialNonmaximumSuppression.html}. ]
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<div>'''The SUSAN filter . . .''' </div>
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<div>Selected </div>
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<div>Zero </div>
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<div>Uses the median of the pixel's 8 nearest neighbors in 2D images or 26 nearest neighbors in 3D images to estimate the pixel's correct value. </div>
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<div>Selected </div>
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<div>Nonzero </div>
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<div>Uses sums taken over the local neighborhood, not including the center pixel itself, to estimate the pixel's correct value. This allows good reduction of impulse noise. </div>
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<div>Not selected </div>
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<div>Nonzero </div>
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<div>Uses sums taken over the local neighborhood including the center pixel to estimate the pixel's correct value. </div>
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<div>Not selected </div>
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<div>Zero </div>
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<div>Leaves the pixel unchanged. </div>
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</div>
<br />


== Image types ==
== Image types ==


You can apply this algorithm to black-and-white 2D, 2.5D, and 3D images.
The nonmaximum suppression image can be generated from 2D, 2.5D, and 3D black-and-white images. However, the option to output an edge image is only available for black-and-white 2D images.
 
== Special notes ==
 
None.


== Applying the algorithm ==
== Applying the Nonmaximum Suppression algorithm ==


To run this algorithm, complete the following steps:
To run this algorithm, complete the following steps:


# Open an image.
# Open an image.
# Select Algorithms &gt; Filter (spatial) &gt; Nonlinear noise reduction. The Nonlinear Noise Reduction dialog box (Figure 1) opens.
# Perform, as an option, any other image processing, such as improving the contrast, on the image.
# Select Algorithms &gt; Filter (spatial) &gt; Nonmaximum suppression. The Nonmaximum suppression dialog box (Figure 1) opens.
# Complete the information in the dialog box.
# Complete the information in the dialog box.
# Click OK. The algorithm begins to run.
# Click OK. The algorithm begins to run.


; A pop-up window appears with the status. The following message appears: "Performing the nonlinear noise reduction." When the algorithm finishes running, the pop-up window closes.
; A pop-up window appears with the status. The following message appears: "Calculating the Nonmaximum suppression."
; Depending on whether you selected New image or Replace image, the results appear in a new window or replace the image to which the algorithm was applied.
; When the algorithm finishes running, the pop-up window closes. Depending on whether you selected New image or Replace image, the results appear in a new window or replace the image to which the algorithm was applied.
 
{| width="90%" border="1" frame="hsides" frame="hsides"
|-
| width="9%" valign="top" |
[[Image:noteicon.gif]]
| width="81%" bgcolor="#B0E0E6" | '''Note:''' For 2D images, if you selected Output edge image, a new window with an edge image appears.
|}
 
<br /><div>
 
== Nonmaximum Suppression dialog box ==
 
{| border="1" cellpadding="5"
{| border="1" cellpadding="5"
|+ <div>'''Figure 1. Nonlinear Noise Reduction dialog box  ''' </div>
|+ <div>'''Figure 1. Nonmaximum Suppression dialog box  ''' </div>
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<div>'''Brightness threshold''' </div>
<div>'''X dimension''' </div>
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<div>Blurs edges of contrast smaller than this threshold. Reducing the brightness threshold gives less smoothing. The default value is 0.1 * (image maximum - image minimum). </div>
<div>Indicates the scale of the Gaussian in the ''X'' direction (the default value is 1.0). </div>
| rowspan="3" colspan="1" |
| rowspan="4" colspan="1" |
<div><div><center>[[Image:dialogboxNonlinearNoiseReduction.jpg]]</center></div> </div><div> </div>
<div><div><center>[[Image:dialogboxNonmaximumSuppression.jpg]]</center></div> </div><div> </div><div> </div><div> </div><div> </div><div> </div><div> </div><div> </div><div> </div><div> </div><div> </div><div> </div><div> </div><div> </div>
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<div>'''Mask Gaussian SD (0 for flat response) mm ''' </div>
<div>'''Y dimension''' </div>
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<div>Determines the spatial extent of the smoothing (the default value is equal to the ''X'' resolution). For a small, fast, flat response with a 3 x 3 or 3 x 3 x 3 voxel mask, set the mask SD to 0. </div>
<div>Indicates the scale of the Gaussian in the ''Y'' direction (the default value is 1.0). </div>
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<div>'''Use median when neighborhood not found''' </div>
<div>'''Z dimension''' </div>
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<div>By default, this check box is selected. </div>
<div>Indicates the scale of the Gaussian in the ''Z'' direction (for 3D images only). The default value is 1.0. </div>
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<div>'''Process each slice independently ''' </div>
<div>'''Use image resolutions to normalize ''''''Z'''''' scale''' </div>
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<div>Normalizes the ''Z'' scale to compensate for the difference if the voxel resolution in distance per pixel is greater between slices than the voxel resolution in-plane (for 3D images only, the default value is enabled).  </div><div>If enabled, then [[Image:FiltersSpatialNonmaximumSuppression3.jpg]] where ''Z'' = scale Z, ''XRs'' = image X resolution, and ''ZRs'' = image Z resolution).  </div>
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<div>'''Process each slice independently''' </div>
| rowspan="1" colspan="2" |
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<div>Smooths each slice of the dataset independently (applies only to 3D images). </div>
<div>Calculates nonmaximum suppression for each slice of the dataset independently (for 3D images only the default value is enabled). </div>
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<div>'''New image''' </div>
<div>'''New image''' </div>
| rowspan="1" colspan="2" |
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<div>Shows the results of the algorithm in a new image window (default choice). </div>
<div>Shows the results of the algorithm in a new image window (default choice). If selected, an output edge image appears in a second new window. </div>
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<div>'''Replace image''' </div>
<div>'''Replace image''' </div>
| rowspan="1" colspan="2" |
| rowspan="1" colspan="2" |
<div>Replaces the current active image with the newly calculated image. </div>
<div>Replaces the current active image with the results of the algorithm. </div>
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<div>'''Whole image''' </div>
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<div>Applies the algorithm to the whole image (default choice). </div>
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<div>'''VOI region(s)''' </div>
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<div>Applies the algorithm inside VOIs. Outside VOIs, the pixel values are unchanged. </div>
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<div>'''Cancel ''' </div>
<div>'''Cancel''' </div>
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<div>Disregards any changes that you made in the dialog box and closes the dialog box. </div>
<div>Disregards any changes that you made iin the dialog box and closes this dialog box. </div>
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== See also: ==
**[[Filters (Spatial): Adaptive Noise Reduction]]
**[[Filters (Frequency)]]
**[[Filters (Spatial): Adaptive Path Smooth]]
**[[Filters (Spatial) Anisotropic Diffusion]]
**[[Filters (Spatial): Coherence-Enhancing Diffusion]]
**[[Filters (Spatial): Gaussian Blur]]
**[[Filters (Spatial): Gradient Magnitude]]
**[[Filters (Spatial): Haralick Texture]]
**[[Filters (Spatial) Laplacian]]
**[[Filters (Spatial): Local Normalization]]
**[[Filters (Spatial): Mean]]
**[[Filters (Spatial): Median]]
**[[Filters (Spatial): Mode]]
**[[Filters (Spatial): Nonmaximum Suppression]]
**[[Filters (Spatial): Regularized Isotropic (Nonlinear) Diffusion]]
**[[Filters (Spatial): Slice Averaging]]
**[[Filters (Spatial): Unsharp Mask]]


[[Category:Help]]
[[Category:Help]]
[[Category:Help:Algorithms]]
[[Category:Help:Algorithms]]

Revision as of 14:49, 21 August 2012

This algorithm defines the edges of an image by calculating the nonmaximum suppression of an image at a user-defined scale. An edge is defined as the union of points for which the gradient magnitude assumes a maximum in the gradient direction.

Noteicon.gif

Algorithms/FiltersSpatialNonmaximumSuppression.html For more information about the algorithm, refer to the MIPAV web site: {http://mipav.cit.nih.gov/documentation/HTML Algorithms/FiltersSpatialNonmaximumSuppression.html}.


Image types

The nonmaximum suppression image can be generated from 2D, 2.5D, and 3D black-and-white images. However, the option to output an edge image is only available for black-and-white 2D images.

Applying the Nonmaximum Suppression algorithm

To run this algorithm, complete the following steps:

  1. Open an image.
  2. Perform, as an option, any other image processing, such as improving the contrast, on the image.
  3. Select Algorithms > Filter (spatial) > Nonmaximum suppression. The Nonmaximum suppression dialog box (Figure 1) opens.
  4. Complete the information in the dialog box.
  5. Click OK. The algorithm begins to run.
A pop-up window appears with the status. The following message appears
"Calculating the Nonmaximum suppression."
When the algorithm finishes running, the pop-up window closes. Depending on whether you selected New image or Replace image, the results appear in a new window or replace the image to which the algorithm was applied.

Noteicon.gif

Note: For 2D images, if you selected Output edge image, a new window with an edge image appears.


Nonmaximum Suppression dialog box

Figure 1. Nonmaximum Suppression dialog box
X dimension
Indicates the scale of the Gaussian in the X direction (the default value is 1.0).
DialogboxNonmaximumSuppression.jpg
Y dimension
Indicates the scale of the Gaussian in the Y direction (the default value is 1.0).
Z dimension
Indicates the scale of the Gaussian in the Z direction (for 3D images only). The default value is 1.0.
Use image resolutions to normalize 'Z' scale
Normalizes the Z scale to compensate for the difference if the voxel resolution in distance per pixel is greater between slices than the voxel resolution in-plane (for 3D images only, the default value is enabled).
If enabled, then FiltersSpatialNonmaximumSuppression3.jpg where Z = scale Z, XRs = image X resolution, and ZRs = image Z resolution).
Process each slice independently
Calculates nonmaximum suppression for each slice of the dataset independently (for 3D images only the default value is enabled).
New image
Shows the results of the algorithm in a new image window (default choice). If selected, an output edge image appears in a second new window.
Replace image
Replaces the current active image with the results of the algorithm.
Whole image
Applies the algorithm to the whole image (default choice).
VOI region(s)
Applies the algorithm inside VOIs. Outside VOIs, the pixel values are unchanged.
OK
Applies the algorithm according to the specifications in this dialog box.
Cancel
Disregards any changes that you made iin the dialog box and closes this dialog box.
Help
Displays online help for this dialog box.
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