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The left image illustrates the usual moiré pattern resulting from a previously screened image (a traditional halftone) on a digital screen device (a flatbed scanner). This happens due to differences in screening registration and resolution. By converting the original image via Fourier transform into a frequency domain, the moiré pattern appears as several singularity points that can be filtered out from the transformed image. The remaining information left in the image is reverted back to the spatial domain via an inverse Fourier transform as illustrated in the right image, which shows no moiré pattern.
