The Complete Guide to Image Compression
Everything about shrinking image files: formats, quality math, workflow and the tools that automate it.
Aria Chen
Senior Tech Editor
Image compression is the highest-ROI performance fix on the modern web. A single well-compressed hero image does more for page speed than a dozen caching tweaks. This guide covers the whole subject — the concepts, the math and the workflow.
Lossy vs lossless: the core concept
Lossless compression (PNG, GIF, lossless WebP) removes redundancy without discarding information — the decoded image is pixel-identical. Lossy compression (JPEG, lossy WebP) removes data the eye will not notice, trading perfect fidelity for dramatically smaller files. For photos, lossy is nearly always the right call; for graphics and screenshots, lossless or near-lossless WebP wins.
Why format choice matters more than settings
Compression settings tune one algorithm. Choosing the right format switches to a better one. A PNG screenshot at any quality is usually larger than the same screenshot as WebP at identical quality, because PNG's lossless algorithm simply has less to work with. Format first, settings second.
The quality/size curve
Quality settings do not behave linearly. Going from 100 to 85 often removes half the file with no visible change; going from 60 to 40 removes visible detail. The useful range is narrow — 70 to 90 — and the sweet spot for web is 75–85. Below that, you are paying visible quality for bytes you could have saved by resizing instead.
Resize before you compress
Compression can only remove redundant data from the file it is given. A 4000px photo carries 4000px of redundancy no matter the quality setting. Resize to the display size first, then compress. The combined reduction routinely reaches 90%+
The recommended workflow
- Resize to the largest display size needed.
- Pick WebP (or JPG for compatibility/email).
- Set quality to 80% and compare with the original.
- Zoom into detailed areas to check for artifacts.
- Keep the original file; ship the compressed copy.
The Image Compressor does the whole job in one place — upload, quality slider, live comparison and download.
What compression ratio should I target?
For photos, 60–80% size reduction is typical at 80% quality. Below 50% of the original, check quality carefully.
Tools for this task
Image Compressor
PopularShrink JPG, PNG and WebP files without losing visible quality.
Resize images to exact dimensions, scales or target sizes.
Convert images between JPG, PNG, WebP, GIF and BMP.
Keep reading
How to Compress Images Without Losing Visible Quality
Cut image file sizes by 80% or more while keeping photos looking sharp. Here is the exact workflow we use, with real numbers.
WebP vs PNG vs JPEG: Which Image Format Should You Use?
Stop guessing. Here is a decision tree for choosing between JPEG, PNG and WebP — with the actual size differences.
