How to compress an image without wrecking it
“Without losing quality” is not quite achievable — lossy compression always loses something. What is achievable, and what this guide is about, is losing nothing you can see.
Resize first. It matters more than the quality slider.
This is the single most useful thing to know, and most people do it last or not at all.
If a 4000-pixel-wide photo is going somewhere that displays it at 1200 pixels, the extra pixels are downloaded and thrown away. Resizing to 1200 first cuts the file to a fraction of its size and costs no visible quality at all, because the pixels you removed were never going to be seen.
Compare that to compressing hard at full resolution: every pixel is kept but every pixel is degraded. A 4000-pixel photo squeezed to 200 KB looks visibly worse than the same photo resized to 1200 pixels and then compressed gently to the same 200 KB.
Resize, then compress. In that order.
Where the quality slider actually matters
The relationship between quality and file size is not linear:
- 100 to 90 — large size savings, no visible change. This range is nearly free.
- 90 to 75 — still substantial savings, still invisible on photographs. This is where you want to be.
- 75 to 50 — savings get smaller, damage starts showing on edges and flat areas.
- Below 50 — very little further saving, obvious damage. Rarely worth it; resize instead.
Going from quality 100 to 90 often halves the file. Going from 50 to 40 might save a few percent and ruin the image. If you are below 60 and still too big, the resolution is the problem, not the quality.
Never compress an already-compressed image
Every lossy pass throws detail away permanently, and the next pass works on the damaged result. Compressing twice at quality 80 looks worse than compressing once at 65, and produces a larger file.
Always start from the best original you have. If you have already saved a compressed copy and need it smaller still, go back to the original and compress once, harder.
Choose the right format for the content
Lossy compression assumes it is looking at a photograph. Where that holds it is nearly invisible; where it does not, damage appears fast.
- Text and screenshots — hard edges get a smudged halo. Stay above quality 85, or use PNG.
- Flat colour — skies and studio backgrounds turn into visible bands. Keep the quality higher than you would for a busy scene.
- Fine repeating detail — fabric, foliage, hair — turns mushy before anything else does.
Switching format is often a bigger win than turning the quality down. The same image as WebP is typically 25–35% smaller than JPG at identical visual quality, which is free size reduction.
Hitting a specific size limit
When a form demands under 2 MB, do this in order: resize to the largest dimensions you actually need, choose WebP if the destination accepts it, then use compress to a target size and let the tool search for the best quality that fits.
Doing it the other way round — crushing the quality of a full-size image until it squeezes under — is how you end up with the blurry, blocky photos everyone recognises on job applications.
Check the result before you use it
View it at the size it will actually be seen at. Compression damage that is obvious at 400% zoom may be entirely invisible at the size it will be displayed — and damage invisible on your phone screen may be glaring in print.