Section 3 · What Digital Images Are Made Of

Resampling

Definition

Changing the pixel count of a raster image, either by discarding pixels (downsampling) or generating new ones through interpolation (upsampling).

Why it matters

Upsampling invents detail that was never captured; it can rescue a slightly undersized image but cannot manufacture sharpness that doesn’t exist. Sourcing at adequate size beats resampling every time.

Example

A 600 px web image upsampled to fill a 5-inch print area looks soft no matter what the ppi field says.

Teaching note

Worth covering before students gather source imagery, not after. The fix for an inadequate source is a different source, and that is only cheap early.