Nanostructures produced on a surface of a silicon wafer by local anodic oxidation (see nanolithography; LAO). Height of structures is 1.0 - 1.6 nm. The size of field is 3x3 micron.

The image is obtained in dynamic mode of scanning. The distortions are caused by temperature drift of piezoscanner and non-uniformity of movement of a probe.

Fourier spectrum of the image (logarithmic scale). The bright vertical strip outside the central area corresponds to horizontal distortions of the initial image.

The combined filter applied on the spectrum. The part of a vertical strip of a spectrum (elimination of horizontal strips on the image) is cut out. All frequency components outside a circle of some radius (low-frequency filtration) are cut out as well.

Restoration of the image using Fourier spectrum after filtering (inverse Fourier transformation). Because the central area of an image (low frequency component of topography) was not exposed to a filtration, the sinuosity of a surface is kept.

The alternative approach is using of a high pass directed filter.

Additional processing using the low-pass Gaussian filter for elimination of high frequency noise.