Image Compressor
Choose an image
Pick a file above and the compressed version appears here. Nothing is uploaded. The image is read and processed in this page.
The compressor re-encodes an image at a lower quality to make the file smaller, showing the before and after sizes as you move the slider. It also offers a width cap, because for most oversized images the pixel count is the real problem and no amount of quality reduction fixes that.
How it works
JPEG and WebP are lossy: the encoder divides the image into blocks, converts each to frequencies, and discards the high-frequency detail the eye is least sensitive to. The quality setting controls how aggressively that discarding happens.
- Quality 90 and above is near-invisible loss and modest savings. Around 75 is the usual sweet spot. Below 60 the block edges and colour smearing become visible, particularly on flat areas and gradients.
- WebP is typically 25 to 35% smaller than JPEG at equivalent visual quality, and is supported by every current browser.
- PNG is lossless, so the quality slider does nothing for it. PNG gets smaller only by reducing dimensions or colour depth.
- Capping the width resizes before encoding, which almost always saves more than the quality setting alone.
Re-encoding an already-compressed JPEG at high quality usually makes it larger, because the encoder is now faithfully preserving the artefacts of the first compression. When that happens the page says so rather than quietly handing back a bigger file.
Examples
A photo at default quality
Quality
75
Result
Typically 60 to 80% smaller than the camera original
Most of the saving comes from the encoder discarding detail a camera stored at maximum quality.
Quality against dimensions
Compare
Quality 50 against halving the width
Result
Halving the width usually wins
Halving both dimensions quarters the pixel count. Dropping quality from 75 to 50 typically saves a third and costs visible artefacts.
Re-encoding a compressed file
Input
A web JPEG at quality 95
Result
Larger than the original, and flagged
The encoder now spends bits preserving the first compression's artefacts. Keeping the original is the right answer.
Frequently asked questions
What quality setting should I use?
75 is a good default for photographs. The loss is hard to see and the saving is large. Go to 85 or 90 for images that will be printed or examined closely, and below 60 only when file size genuinely matters more than appearance.
Why did compressing make my file bigger?
Because it was already compressed. Re-encoding a JPEG at a high quality setting makes the encoder faithfully preserve the artefacts left by the first pass, which costs more bits than the original detail did. Either lower the quality, cap the width, or keep what you have.
Does the quality slider affect PNG?
No. PNG compression is lossless. It reproduces the original pixels exactly, so there is no quality dial to turn. A PNG gets smaller only by reducing its dimensions or its colour palette. If you need a smaller photograph, use JPEG or WebP.
Should I use WebP?
For the web, usually yes. It is typically 25 to 35% smaller than JPEG at the same visual quality and every current browser supports it. The caveat is outside the browser: some desktop applications, older email clients and print workflows still will not open a WebP.
Can I get back to the original quality afterwards?
No. Lossy compression discards information permanently. The detail is not recoverable from the compressed file. Always keep the original somewhere, and compress a copy.
Why does compressing the same image twice keep degrading it?
Because each pass re-quantises what the previous pass already quantised, and the errors accumulate. This is generation loss. Compress from the original every time rather than compressing an already-compressed file.