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Evaluation Processing and Filtering

Process of Evaluation

The parameters used in ISO 25178 Surface Texture are calculated based on the following:

  1. Obtain the primary surface by surface filtering (using the S-filter) the real surface.
  2. Based on the evaluation results, perform further surface filtering (using the F-operator and the L-filter) to obtain the scale-limited surface.
  3. Specify the evaluation area from the scale-limited surface.
  4. Obtain the reference surface for the scale-limited surface and calculate the parameters.


The standards for filtering are still under review by the International Organization for Standardization (ISO).

This section introduces the filtering methods being evaluated by ISO for the S-filter and the L-filter.

Gaussian filter

The Gaussian filter (named for Carl Gauss) is one kind of smoothing filter that suppresses noise using the Gaussian function. Gaussian filters that are specified in JIS B 0632:2001 (ISO 11562:1996) and ISO 16610-21:2011 are applied to areal surface roughness measurements.

Spline filter

The spline filter is one kind of filter used to obtain a smooth profile by interpolating the sections between effective adjacent points using the spline function. Spline filters that are specified in ISO/TS 16610-22:2006 are applied to areal surface roughness measurements.

S-filter and L-filter settings

Cutoff wavelength for S-filter

A value equal to or more than 3 times the measurement resolution for the XY plane (horizontal plane) is used. If the set value is not sufficiently effective, increase the set value until the scale-limited surface noise is removed. If a different kind of filtering was applied beforehand, this may not be used.

Cutoff wavelength for L-filter

The cutoff wavelength for the L-filter is difficult to uniformly specify based on lens magnification or stylus tip diameter; therefore, it must be adjusted with reference to the real surface. Set a value 5 times the XY-directional length of the profile that you want to remove as waviness.


Profile 1 Horizontal distance
Section 1 14.678 μm 0.58 Mil

In the example above, the cutoff value is 0.1 mm 0.004".

14.678 x 5 = 73.39 ≈ 0.1 mm 0.004"

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