Image Compressor

Features

• JPEG, WebP and PNG output
• Adjustable quality with a live size readout
• Optional maximum width, which usually saves more than quality does
• Side-by-side before and after preview
• Nothing is uploaded

How to use it

1. Drop an image, or click to browse.
2. Adjust the quality slider and watch the size change.
3. Limit the width if the image is larger than it needs to be.
4. Download when you are happy with the result.

Where the savings actually come from

Resizing usually beats quality reduction. File size scales with pixel count, so halving an image's width quarters its pixels and typically cuts the file to around a quarter of its original size, with no visible loss at all if the image was larger than its display size. A 4000-pixel-wide photo displayed in a 800-pixel column is carrying 25 times more data than the screen can use. Check the width limit before reaching for aggressive quality settings.

JPEG quality is not a percentage of anything meaningful. It is an index into quantisation tables, and the relationship to file size is steeply non-linear: dropping from 100 to 85 often halves the file with no perceptible difference, while dropping from 50 to 35 saves comparatively little and looks noticeably worse. Somewhere between 75 and 85 is the sweet spot for most photographs.

Format matters more than either. WebP is typically 25% to 35% smaller than JPEG at equivalent visual quality and is now supported by every current browser. It also supports transparency, which JPEG does not. The one case for PNG is images with sharp edges and flat colour, screenshots, logos, diagrams, where JPEG's block-based compression produces visible artefacts around text. Never re-compress a JPEG repeatedly, since each pass discards more information permanently.