Distinguish between aliasing and Moiré; why are they concerns in digital imaging?

• A. Aliasing is the misrepresentation of low-frequency content due to sampling.
• B. Moiré is the general misrepresentation of high-frequency content due to sampling.
• C. Aliasing and Moiré are entirely unrelated phenomena.
• D. Aliasing is the general misrepresentation of high-frequency content due to sampling; Moiré is a specific grid-interference pattern; both degrade image quality and require careful sampling/grid choices.

Answer: (D)

Think about how a digital sensor turns a continuous scene into a grid of pixels. If the scene has detail that changes faster than the sensor can sample (the Nyquist limit), that information can’t be captured faithfully. This leads to aliasing, where high-frequency content folds into lower frequencies and the image looks distorted, with jagged edges or strange shapes.

Moiré is a particular kind of artifact that appears when a fine, repeating pattern in the subject (like fabric weaves, lattices, or tiny screen dots) interacts with the sensor’s regular pixel grid. This interaction creates new, visible interference patterns that aren’t part of the original scene. So Moiré is a specific manifestation of aliasing tied to repetitive patterns and grid alignment.

Both issues reduce image quality and are mitigated by careful sampling choices: using higher sensor resolution or pre-filtering to remove problematic high frequencies before sampling, aligning or designing patterns to avoid strong interactions with the grid, and applying proper downsampling with filtering when resizing images.