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Image Compressor

Reduce image file size in your browser, with the original never leaving your device.

Runs entirely in your browser — nothing you enter is uploaded.

How to use Image Compressor

  1. Drop an image onto the page, or choose a file.
  2. Drag the quality slider — lower values give a smaller file at the cost of visible detail.
  3. Choose an output format: JPEG, WebP or PNG.
  4. Compare the before-and-after preview, then download the result.

How this works

The image is decoded to a canvas and re-encoded at the quality level you choose. JPEG and WebP use lossy compression: the encoder discards high-frequency detail the eye is least sensitive to, and the quality setting controls how aggressively. WebP typically reaches a given visual quality at 25–35% smaller than JPEG because it uses better prediction and entropy coding. All of this uses the browser's own codecs, so the file is read locally and nothing is transmitted or stored.

Assumptions

  • Processing is limited by your device's memory. Very large images may fail on mobile.
  • Re-encoding is generational — compressing an already-compressed JPEG loses more detail, because the artefacts of the first pass get encoded too.
  • EXIF metadata, including location and camera information, is removed during re-encoding.
  • PNG output is lossless, so the reduction comes from re-encoding rather than quality loss and is usually modest.

Worked example

A 4.2 MB photograph from a phone camera, re-encoded as JPEG at quality 80.

Original
4.2 MB JPEG, 4032 × 3024
Quality
80
Result
About 620 KB — an 85% reduction

Most of the saving comes from the original being written at near-maximum quality by the camera, which is far beyond what is perceptible. Dropping to quality 80 is visually near-identical at normal viewing sizes. Going further to quality 60 would reach roughly 380 KB, at which point flat areas such as skies begin to show visible banding.

How to read the result

Quality 75–85 is the practical range for photographs on the web: below 70, compression artefacts become visible in gradients and around sharp edges; above 90, the file grows quickly for detail almost nobody can see. If the result is barely smaller than the original, the image was already well compressed and further passes will only degrade it. Compare the before-and-after preview at full size rather than trusting the percentage alone.

Limitations

  • Compressing an image repeatedly degrades it cumulatively. Always work from the original, not a previously compressed copy.
  • Removing EXIF is good for privacy but also strips copyright and colour-profile information you may need.
  • Images with transparency must stay PNG or WebP; JPEG has no alpha channel and will fill transparent areas.
  • Large files are constrained by browser memory rather than by any server limit.

Frequently asked questions

Is my photo uploaded to a server?
No. The image is read, decoded and re-encoded entirely in your browser using the canvas API — it never leaves your device, as described above.
Which format should I choose?
WebP for the smallest file at a given visual quality, if the platform you're using it on supports it. JPEG for the widest compatibility. PNG only if you need transparency or the image is already lossless (screenshots, graphics with flat colour), since PNG won't shrink photographs much.
Why is the compressed file barely smaller?
The original was probably already well compressed — cameras and phones often save at near-maximum JPEG quality, so there isn't much redundancy left to remove. Compressing it further will mostly just lose quality rather than save meaningful space.