Every image on the web is a trade-off between file size and quality, and the format you pick decides where that trade-off lands before you've adjusted a single slider. Here's the short version, followed by the reasoning.
The quick answer
- Photos and complex gradients → JPG (or WebP if your platform supports it)
- Logos, icons, screenshots with text, or anything needing transparency → PNG
- Anywhere you control the delivery pipeline and want the smallest file at equal quality → WebP
Why JPG exists — and its one real weakness
JPG uses lossy compression tuned for photographic detail: it throws away color information the human eye is less sensitive to and keeps the rest. That makes it extremely efficient for photos — a JPG can be 1/10th the size of the equivalent PNG with barely perceptible quality loss. Its weakness is anything with sharp edges or flat color: text, logos, and line art develop visible "ringing" artifacts around edges because JPG's compression algorithm wasn't designed for hard transitions.
Why PNG exists — and why it's not always better
PNG is lossless — every pixel is preserved exactly — and it supports an alpha (transparency) channel, which JPG doesn't. That makes it the right choice for logos, UI screenshots, and any image that needs a transparent background. The cost is file size: PNG compresses flat-color graphics well but handles photographic detail poorly, often producing files 5-10x larger than an equivalent JPG for the same photo.
Where WebP fits in
WebP is a newer format built to take the best of both: it supports both lossy compression (like JPG, but typically 25-35% smaller at equivalent quality) and lossless compression with transparency (like PNG, but smaller). Browser support is now near-universal, which is why most performance-conscious sites serve WebP by default and fall back to JPG/PNG only for older tools that don't read it (some design software, older email clients, certain CMS plugins).
Quick comparison
- File size for a typical photo: PNG (largest) > JPG > WebP (smallest)
- Transparency support: PNG yes, WebP yes, JPG no
- Best for text/logos: PNG or WebP lossless, not JPG
- Universal compatibility (old software, print workflows): JPG and PNG win
If you're not sure which to pick, convert a copy in a couple of formats and compare the file sizes and visual quality side by side — that's faster than memorizing the rules above. The converter handles JPG, PNG, and WebP in both directions, entirely in your browser, so you can test without uploading anything.