How to Reduce Image File Size Without Making It Look Bad
File size depends on three things, in this order of impact: pixel dimensions, format and compression quality.
1. Use the dimensions you actually need
A 4000 × 3000 phone photo has 12 million pixels. Shown 1200 pixels wide on a web page, about 90% of them are wasted. Halving the width and height cuts the pixel count by 75%, which often shrinks the file more than any quality setting. Start with Resize Image.
2. Pick the right format
Photos belong in JPG or WebP, not PNG. Graphics with few colors often shrink dramatically as a palette PNG or a WebP. See JPG vs PNG vs WebP: Which Image Format Should You Use?.
3. Then lower quality, carefully
For JPG and WebP, quality 70–80 is usually indistinguishable from the original at normal viewing size. Below about 60, you'll start to see blocky skies, smeared fine texture and halos around text. Compress Image shows the exact size saved for each file, so you can stop when it's small enough.
When a form needs a maximum size
Compress to KB searches for the highest quality that fits under a target such as 100 KB. If that's still too big, it reduces the dimensions too, and tells you when it does.
What not to do
- Don't compress the same JPG repeatedly: each round adds loss. Keep the original and compress once.
- Don't trust “lossless” promises for photos: real savings on photos come from lossy compression. See Lossy vs Lossless Image Compression.