Section 3 · What Digital Images Are Made Of

Resolution: Native vs. Effective

Definition

Native resolution is the pixel dimensions an image actually contains. Effective resolution is the pixel density it delivers at the size it has been placed — native pixels divided by final placed dimensions.

Why it matters

An image can be 300 ppi in its own file and 90 ppi on the page, because it was scaled up after placement. Effective resolution is the only number that predicts what the print will look like.

Example

A 3000 × 3000 px image is 300 ppi at 10 × 10 inches, but only 150 ppi if enlarged to fill a 20 × 20 inch area.

Teaching note

This is the most common cause of a failed first print, and students cannot diagnose it from inside the image editor — the number they need is reported by the layout application’s links inventory (Section 10). Teach the two together.