Images are usually the heaviest part of a web page. Shrinking them is the quickest speed win, and it takes three decisions: dimensions, format and quality.
1. Resize first
A 4000 pixel wide photo displayed in a 800 pixel column wastes most of its bytes. Resize to roughly twice the display width for sharp screens, then compress.
2. Pick the right format
- JPG suits photos with many colors.
- PNG suits logos, screenshots and anything needing transparency.
- WebP is usually 25 to 35 percent smaller than JPG at similar quality and is supported by every modern browser.
3. Lower the quality a little
Quality between 70 and 85 percent is a sweet spot for photos. Differences are hard to see, but file size drops sharply. Always compare the result at full size before you publish.
You can do all three steps without uploading anything: use the image resizer, the image converter and the image compressor. Everything runs inside your browser.