Image basics

Image dimensions, aspect ratio, and print size

A few measurements describe different things. Understanding them helps you resize a photo without stretching it or expecting a screen image to print at an arbitrary size.

Pixels describe the image grid

An image that is 1200 by 800 pixels contains 1200 columns and 800 rows of samples. Reducing those values lowers the amount of spatial detail available. Increasing them through ordinary resizing creates interpolated pixels; it does not restore detail that was not captured.

Aspect ratio describes shape

Aspect ratio compares width to height. A 1200 × 800 image is 3:2. To preserve the shape while resizing, multiply both dimensions by the same scale factor. For example, scaling the width to 900 pixels also scales the height to 600 pixels. If a destination asks for a square image, crop to a square before resizing.

DPI connects pixels to print dimensions

For a chosen print resolution, approximate print width in inches by dividing pixel width by DPI; do the same for height. A 2400 × 3000 image at 300 DPI corresponds to about 8 × 10 inches. DPI here is a planning value. It does not automatically alter the number of pixels or guarantee print quality.

When to crop and when to resize

Crop when the subject needs different framing or a required shape. Resize when the shape is right but pixel count is too large or too small. Check minimum dimensions before reducing an image.

Try the aspect-ratio and print-size calculators, then prepare the image in the ResizeTool workspace.