Speckle Filter

Speckle Filter Operator

SAR images have inherent salt and pepper like texturing called speckles which degrade the quality of the image and make interpretation of features more difficult. Speckles are caused by random constructive and destructive interference of the de-phased but coherent return waves scattered by the elementary scatters within each resolution cell. Speckle noise reduction can be applied either by spatial filtering or multilook processing.

Filters Supported

The operator supports the following speckle filters for handling speckle noise of different distributions (Gaussian, multiplicative or Gamma):

Parameters Used

   For most filters, the following parameters should be selected (see figure 1 for example):
  1. Source Band: All bands (real or virtual) of the source product. User can select one or more bands for producing filtered images. If no bands are selected, then by default all bands will be selected. For complex product, only the intensity band can be selected.
  2. Filter: The speckle filter.
  3. Size X: The filtering kernel width.
  4. Size Y: The filtering kernel height.
  5. Frost Damping Factor: The damping factor for Frost filter.


                             Figure 1. Dialog box for Mean filter.

For Frost filter, one extra parameter should be selected (see figure 2):
  1. Frost Damping Factor: The damping factor for Frost filter.


                               Figure 2. Dialog box for Frost filter

For Refined Lee filter,  the following parameter should be selected (see Figure 3):
  1. Edge Threshold: A threshold for detecting edges.  Area of 7x7 pixels with local variance lower than this threshold is considered flat  and normal Local Statistics Filter is used for the filtering. If the local variance is greater than the threshold, then the area is considered as edge area and Refined Lee filter will be used for the filtering.



                              Figure 3. Dialog box for Refined Lee filter.

Reference: 

[1] J. S. Lee, E. Pottier, Polarimetric SAR Radar Imaging: From Basic to Applications, CRC Press, Taylor & Francis Group, 2009.

[2] G. S. Robinson, “Edge Detection by Compass Gradient Masks”, Computer Graphics and Image Processing, vol. 6, No. 5, Oct. 1977, pp 492-502.

[3] V. S. Frost, J. A. Stiles, K. S. Shanmugan, J. C. Holtzman, \A Model for Radar Images and Its Application to Adaptive Digital Filtering of Multiplicative Noise", IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. PAMI-4, pp. 157-166, 1982

[4] Mansourpour M., Rajabi M.A., Blais J.A.R., “Effects and Performance of Speckle Noise Reduction Filters on Active Radar and SAR Images”, http://people.ucalgary.ca/~blais/Mansourpour2006.pdf