Three ways to set the size
- Exact pixels: when you need a specific number such as 800px wide. Keep the aspect ratio on and the height follows.
- Percentage: scale the original down to 50% in one move.
- Longest side: normalise a mixed set of portrait and landscape photos to the same maximum edge.
How this differs from cropping
Resizing keeps the whole frame and changes its size. If the aspect ratio has to change and part of the picture must go, use the image cropper; if the dimensions should stay and only the file size matters, use image compression. For passport specs in millimetres, use the passport photo resizer.
Format and file size
WebP gives the smallest file at a comparable quality. JPEG has no transparency, so transparent areas are filled with white. Move the quality slider and the resulting size updates immediately.
Quality
Downscaling loses almost nothing. Upscaling invents pixels that were never captured and looks soft, so start from a larger original when the result is meant for print.