Compression is the single highest-leverage thing you can do to speed up a page — but "just compress it" hides a few important choices. Here's what's actually happening, and how to get the smallest file without a visible quality hit.
Image compression reduces file size by encoding the same picture with less data. There are two kinds, and the difference matters:
For photographs, lossy compression at a sensible quality level is almost always the right call: the file gets far smaller and, at normal viewing distances, looks identical.
Every lossy compressor exposes a "quality" setting, usually 0–100. Counter-intuitively, dropping from 100 to about 80 typically removes half the file size while producing no visible difference. Below roughly 60 you start to see artifacts. The sweet spot for most web images is 75–85.
See it yourself: the Resizely compressor shows a live before/after slider so you can push the quality down until you just start to notice a change, then back off one notch. That's your optimal setting — and it all happens in your browser, so nothing is uploaded.
Try the compressor →The format you compress to matters as much as the quality slider. At the same visual quality, WebP is usually 25–35% smaller than JPG, and AVIF can be smaller still. Converting a JPG to WebP with our converter before (or instead of) heavy compression often gets you a smaller file with better quality.
If you're also cropping and resizing, do those first: a smaller image has less data to compress, so you get a cleaner result. The all-in-one editor handles the whole chain — crop, resize, convert, then compress — in one pass, and can batch up to 20 images at once.
Smaller images mean faster pages, and speed feeds directly into rankings and conversions. If you want the bigger picture, see how to speed up website images and the complete image SEO guide.