Almost every image you publish is larger than it needs to be. A photo straight from a phone can be 4–8 MB, yet the same picture displayed on a web page at 1200 pixels wide looks identical at 200 KB. The trick is knowing which knobs to turn — and which ones cost you visible quality.
Lossy compression (JPG, WebP) permanently discards detail the eye is unlikely to notice. You choose a quality level, and the encoder throws away data to hit it. Do it once at quality 85 and nobody can tell; do it ten times and the image turns to mush.
Lossless compression (PNG, and WebP in lossless mode) keeps every pixel exactly. It can only shrink so much — typically 5–25% — but you can re-save the file as many times as you like.
The practical rule: use lossy for photographs, lossless for screenshots, logos, diagrams and anything with text or hard edges.
This is the single biggest win, and most people skip it. A 6000 × 4000 photo displayed in a 600-pixel-wide column contains 100× more pixels than anyone will ever see. Halving the width quarters the pixel count, which usually cuts the file to a quarter of the size — with far less quality loss than aggressive JPEG compression.
JPEG quality is not linear. The sweet spot for photos is 80–85, where the file is roughly half the size of quality 95 with no visible difference on a normal screen. Below 70 you start to see blocking around sharp edges and skin tones; below 50 it is obvious.
WebP beats JPG by roughly 25–35% at the same perceived quality, which is why it is worth converting web images. Browser support has been universal since 2020, so there is little reason not to use it for anything that goes on a site.
EXIF blocks (camera model, lens, GPS, thumbnail preview) can add 20–80 KB to every photo. For web publishing that is pure waste — and for privacy reasons you may not want the GPS coordinates going out anyway. Re-encoding through a canvas removes all of it automatically.
Re-saving a JPG repeatedly. Every save re-applies compression. Always work from the original file, not from an already-compressed copy.
Compressing a screenshot as JPG. Text and UI edges are exactly what JPEG destroys. Use PNG or lossless WebP for screenshots; converting a 2 MB PNG screenshot to JPG often produces a blurry mess that is barely smaller.
Scaling up after compressing. Compression artefacts get magnified along with everything else. Resize first, compress last.
Image compression does not need a server. Modern browsers can decode, resize and re-encode an image entirely in memory, which means your photos never leave your device — worth caring about when the pictures are personal documents, ID scans or client work.
Try it now: Compress Image · Convert Image