MLUnsold Digital Imaging

Removing Structured Noise in the Frequency Domain

A color or monochrome image can be split into color, red, green, blue, or luminance spectra in the requency domain. Periodic noise is removed from the image by painting black on the spectrum in the frequency doiman before the image is reconstructed in the normal spatial domain.

Low contrast image with periodic vertical line noise is shown on left. Same image is shown on right after periodic vertical line noise is removed by painting black or 0 on the problem frequencies in the image spectrum. Note that there is no loss of fine image detail or color after the lines are removed.

Problem vertical line frequencies appear as bright spikes along the "x-axis" or "y-axis" of the spectrum shown on right. Spectrum shown on left has vertical line frequencies removed by painting with black = 0 on the problem frequences. For details on painting the spectrum see the Compute, Display, & Remove Residual Structured Noise After Calibration and Stacking tutorial.