If the sampling frequency is less than the Nyquist value, which artifact can occur?

• A. Blurring
• B. Moire effect
• C. Quantum noise
• D. Edge enhancement

Answer: (B)

When sampling is below Nyquist, aliasing occurs. If the sampling frequency isn’t high enough to capture the finest details, those high-frequency components are misrepresented as lower frequencies in the reconstructed image. This creates moiré patterns—bright, wavy interference patterns that look like new, artificial textures across the image.

Blurring would come from insufficient spatial resolution or spreading of signal, not the specific aliasing artifact caused by undersampling. Quantum noise is random variation from photon statistics, not a sampling-rate issue. Edge enhancement is a processing effect that exaggerates edges, not a direct result of undersampling.

So, undersampling at a rate below Nyquist specifically leads to aliasing, which manifests as moiré patterns. To prevent it, increase the sampling rate or apply anti-aliasing measures before sampling.