Image Compressor
About Image Compressor
Drop an image, choose a quality between 1 and 100, and you get a compressed JPEG back with a before/after size. It all runs in the browser through CompressorJS; the image is never uploaded.
What the quality number means
It is the JPEG quality parameter, not a percentage of the original file size. 70 is a sensible default: most photos look unchanged and drop to about a third. Below 50 you start seeing blocking in flat areas like sky. Above 85 the file grows quickly for detail nobody will notice.
Two things to keep in mind. The output is always JPEG, so transparency is flattened — a transparent PNG logo comes back with a background. And compressing an already-compressed file again keeps degrading it, so start from the original each time.
When the result is bigger than the input
That happens with images that were optimized already: screenshots, images from a CDN, anything that has been through a compressor. Re-encoding cannot recover what was thrown away, so the file can grow. If the tool reports no gain, keep the original.
Also worth saying: on the web the bigger win is usually resizing, not quality. A 4000px photo displayed at 800px is wasted bytes however well you compress it.
Frequently asked questions
Does quality 70 mean 70% of the original size?
No. It is the JPEG quality setting, which affects size and visible detail non-linearly. Start at 70, look at the result, then decide whether to go lower.
Why did my PNG come back as JPEG?
The compressor always outputs JPEG. That is also why transparency disappears — JPEG has no alpha channel.
The compressed file is larger than the original. Why?
The original was compressed already. Re-encoding a stripped image adds overhead instead of removing data, so keep the original in that case.
Is the image uploaded anywhere?
No. Decoding and re-encoding happen in the browser, which is also why very large images take a moment and can fail on phones with little memory.
