How compression works
What actually changes in your file, and what doesn't.
Images get smaller by storing less detail you can't see (lossy JPG and WebP), by finding a more efficient encoding of the same pixels (lossless PNG), or by having fewer pixels.
Images
| JPG | Re-encoded with an optimized JPEG encoder at quality 85 / 75 / 60 (High / Balanced / Smaller). |
|---|---|
| WebP | Re-encoded at quality 82 / 72 / 55. |
| PNG | Lossless re-compression by default; optional palette reduction (lossy) when you allow it. |
| Metadata | EXIF orientation applied, then camera/location metadata removed; colour profile kept. |
| Target size | Highest quality that fits, found by binary search; dimensions reduced in steps only if needed. |
Why some files can't get smaller
A file that was already compressed efficiently, like a well-optimized PNG or a low-quality JPG, has little left to remove. Forcing it smaller would mean visibly damaging it. We report 0% in that case.
Measuring the result
Sizes are counted in bytes and shown in decimal units: 1 KB = 1,000 bytes and 1 MB = 1,000,000 bytes. The percentage saved is calculated from those exact byte counts.