The Basic Filters tool lets you apply several simple filters to your image. This can be very useful for data denoising; however, the real measured data will get altered in the process, so great care should be taken not to destroy important features of the image.
Moreover, there are more denoising functions in Gwyddion, for example DWT denoising and FFT filtering. For details see section Extended Data Edit.
If you need to only suppress some values in the SPM data that are obviously wrong, you can also try the Mask of Outliers module and the Remove Data Under Mask module. For details see section Data Edit.
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Convolutions with arbitrary kernels up to 9 × 9 can be performed with the Convolution Filter module.
The Divisor entry represents a common factor all the coefficients are divided before applying the filter. This allows to use denormalized coefficients that are often nicer numbers. The normalization can be also calculated automatically when automatic is checked. When the sum of the coefficients is nonzero, it makes the filter sum-preserving, i.e. it the factor normalizes the sum of coefficients to unity. When the sum of the coefficients is zero, the automatic factor is simply let equal to 1.
Since many filters used in practice exhibit various types of symmetry, the coefficients can be automatically completed according to the selected symmetry type (odd, even). Note the completion is performed on pressing Enter in the coefficient entry.
In a fresh installation only a sample Identity filter is present (which is not particularly useful as it does nothing). This filter cannot be modified, to create a new filter use the New button on the Presets page.