Image compressor

Your image does not go anywhere

There is no upload step here, and that is a fact about how the page is built rather than a promise about how it is operated. The file is read by JavaScript running in your own tab, drawn onto a canvas, encoded again, and handed back as a download. No part of it is sent to a server, because there is no code on this page that sends anything anywhere.

You can check it: load the page, turn off your network connection, and compress an image. It works exactly the same. Close the tab and the compressed version is gone too. It was only ever in memory.

What compression actually changes

The picture is re-encoded at a lower quality. A lossy encoder discards detail the eye is poor at noticing, small variations inside flat areas, fine gradations of colour, and the lower the setting, the more of it goes. The dimensions do not change. A 4,000 × 3,000 photograph is still 4,000 × 3,000 afterwards; only the file size falls.

If you want the picture physically smaller, fewer pixels, for a web page or an email, that is resizing, and it usually saves far more than quality alone. The two work well together: resize first, then compress.

Where to put the slider

Around 75 is the honest default. JPEG’s quality curve is steep at the bottom and flat at the top: below about 60 the artefacts become visible in skies and skin, and above about 85 the file grows quickly to preserve detail almost nobody can see.

It depends on the picture, though. Photographs with lots of texture hide compression well and can go lower. Flat colour, sharp edges, text and screenshots show it immediately and need a higher setting, or a different format entirely.

Why a PNG becomes a JPEG

PNG is lossless. There is no quality dial to turn down, which is exactly why it is the right format for screenshots and logos and the wrong one to ask this tool to compress.

A browser canvas can write a PNG, but its encoder is a plain one, no palette reduction, no filter search, so a PNG that has been through a real optimiser comes back larger than it went in. Rather than do that and call it compression, this converts to JPEG or WebP, which genuinely can be made smaller, and says so on the result.

If your PNG needs to stay a PNG, this is not the tool. A dedicated PNG optimiser reduces the colour count instead, which is a different technique this deliberately does not ship.

JPEG or WebP

WebP is typically 25–35% smaller than JPEG at a visually equivalent quality, and it can hold transparency. Every current browser displays it, and it is the better choice for anything going on a web page.

JPEG opens in everything, including software from decades ago, print shops, older photo frames and the occasional stubborn email client. If the file is going to someone else and you do not know what they will open it with, JPEG is the safe answer.

When the result comes out bigger

It happens, and the tool tells you when it does rather than hiding it. Two common causes: the quality is set higher than the original was saved at, so you are paying bytes to re-encode detail that has already been discarded; or the image is the sort a lossy format handles badly, where JPEG spends bytes trying to reproduce sharp edges it is not built for.

In either case the answer is the same: lower the quality, or keep the file you already had. Compressing an already-compressed image is not free, and each round trip loses a little more.