Edge Enhancing Coherence Filter in the Image Filters Panel

Perform Anisotropic Non-Linear Diffusion filtering on a 2D gray/color or 3D image stack. Anisotropic Non-Linear Diffusion filtering should reduce the noise while preserving the region edges, and also enhancing the edges by smoothing along them.

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Coherence Filter Toolbox description

Image Edge Enhancing Coherence Filter based on the Image Edge Enhancing Coherence Filter Toolbox written by Dirk-Jan Kroon and Pascal Getreuer. This is one of the most advanced image enhancement methods available, and also contains HDCS (Hybrid Diffusion With Continuous Switch), from October 2009. The result looks like an artist painted the image, with clear brush strokes along the image edges and ridges.

The basis of the method used is the one introduced by Weickert.

  1. Calculate Hessian from every pixel of the Gaussian smoothed input image
  2. Gaussian Smooth the Hessian, and calculate its eigenvectors and values (image edges give large eigenvalues, and the eigenvectors corresponding to those eigenvalues describes the direction of the edge)
  3. The eigenvectors are used as diffusion tensor directions. The amplitude of the diffusion in those 3 directions is based on the eigen values and determined by Weickerts equation
  4. A Finite Difference scheme is used to do the diffusion
  5. Back to step 1, till certain diffusion time is reached

Diffusion schemes:

There are several diffusion schemes available: standard, implicit, nonegative discretization, and also a rotation invariant scheme, and a novel diffusion scheme with new optimized derivatives.

Coherence Filter Parameters

Schemes, available numerical diffusion schemes:

Eigenmode, different equations to make a diffusion tensor:

Other parameters

Effective combinations

Coherence Filter Usage

Anisotropic Diffusion is fairly slow process and search of best parameters may be hard. In order to speed up the process there is a possibility to perform a Test run to define the best parameters.

Test run

Coherence Filter References

Parallel processing

There is a small optimization for parallel processing for final runs in 2D mode. The improvement factor is about x3-5 times for 8 cores. Parallel processing should be enabled by pressing the Turn on parallel processing button in the im_browser toolbar .

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