Reducing image file sizes without visible quality loss
By the Converterzilla Team
We build privacy-first PDF and image tools that run entirely in your browser. Our team has shipped JavaScript file-processing apps used by thousands every day, and we write here about the libraries, trade-offs and patterns we use.
"Lossless" compression has a marketing definition (no quality lost) and a practical definition (no quality you'd ever notice). For everyday image use, the practical definition is what matters — and it lets you shrink files dramatically.
JPG quality is logarithmic
Going from 100% to 95% saves about 30% of the file size with zero visible difference. Going from 95% to 85% saves another 30% with a difference you'd only spot on close pixel-peeping. Below 85% the artifacts start showing up.
The bigger win: resolution
A 4000×3000 photo is gorgeous on a print but wasteful on a phone screen that's 1170 pixels wide. Halving the resolution to 2000×1500 cuts file size to a quarter, with no visible difference at any normal viewing distance.
- Email attachments — resize to 2000px on the long edge, JPG quality 90%
- Website hero images — 1920px wide, WebP quality 85%
- Thumbnails — 400px square, JPG quality 80%
- Print — full resolution, JPG quality 95%+
One pass, both knobs
For maximum savings, resize first, then re-encode. Resizing alone is the bigger lever; re-encoding alone is the smaller one. Doing both in one pass is what most batch image processors do under the hood.
Use our image converter to re-encode at lower JPG quality, or wait for the upcoming Compress Images tool which will do both knobs in one operation.