How to Compress an Image Without Visible Quality Loss
"Compress without losing quality" is one of those phrases that sounds like marketing. Of course compression loses quality — that's how it works. But the phrase isn't actually wrong, because the loss is measured against the limit of human perception, not against the raw bytes. A JPG at quality 85% is mathematically a worse image than the same JPG at quality 100%. It is also indistinguishable to your eye. The "without quality loss" promise is true at human resolution, even if it's false at pixel resolution.
The trick is knowing where the line sits, and not crossing it.
The cliff is around 80%
JPG quality settings are roughly logarithmic. The drop from 100% to 90% removes a lot of bytes and zero perceived quality. The drop from 90% to 80% removes more bytes and still zero perceived quality. The drop from 80% to 70% starts being visible — slight smearing in skies, blockiness around edges. Below 70% it's obvious.
Practical defaults that work for almost every case:
- 85% — the standard. About 65–75% file size reduction vs. uncompressed. Use unless you have a specific reason.
- 75% — aggressive but still acceptable for screen viewing. ~80% reduction.
- 60–65% — visibly degraded. Only for thumbnails or extreme size budgets.
Most photo editors save JPGs at 85–92% by default for exactly this reason — that's the sweet spot the entire industry agrees on.
Compress in your browser
Buncha's Image Compressor handles this client-side. Drop one or many images, pick a quality, download. Nothing uploads. The compression uses <canvas> to re-encode the image in your browser; no library needed beyond what the browser already ships with.
The tool shows the before / after file size so you can dial in the right balance. A typical 4 MB photo becomes:
- 1.2 MB at 85%
- 700 KB at 75%
- 400 KB at 60%
PNG compression — different rules
PNG is lossless. There's no "quality slider"; the file is exactly the input pixels. PNG compression works by reducing the colour palette (PNG-8 vs. PNG-24) or by smarter run-length encoding (Zopfli, OxiPNG).
For typical PNGs (screenshots, logos, diagrams), the compressor does palette reduction — drops 24-bit colour to 8-bit if the image has fewer than 256 unique colours, which most logos and diagrams do. This can halve the file size with literally zero quality loss. For complex PNGs (photos saved as PNG by mistake), the right answer is converting to JPG instead — see PNG to JPG.
The "compress twice" mistake
JPG compression is non-idempotent: compressing an already-compressed JPG drops more quality every time. If you compress your photo down to 1 MB at 85%, then later compress that file at 85% again, you've effectively compressed at ~72%. Three rounds and you're at 60%-territory quality.
The fix: always compress from the original. If you've lost the original, accept that further rounds make things worse and stop after one.
WebP — when to use it instead
WebP at the same visual quality as JPG is typically 25–35% smaller. For web-only images (your blog, your portfolio, your marketing site) WebP is strictly better. The catch is that WebP doesn't display in old software, email clients, or Word documents.
If you're compressing for the web, the bulk converter can convert and compress to WebP in one pass. If you're compressing for general distribution, stay with JPG.
Resizing helps more than compressing
The single biggest file-size win is resizing the image down to the size you actually need. A 4032×3024 iPhone photo doesn't need to be 12 MP if you're emailing it; resize to 1920×1440 first, then compress. The combined save is far more than compression alone.
The Image Resizer does this in the browser. Resize first, then compress, then send.
The shortest path
Open the compressor, drop the image, pick 85% quality, download. If your destination has a hard size limit and 85% isn't enough, drop to 75% and check the result before going lower.