Compress Image

What Compress Image does

Compress Image re-encodes a picture so the file gets smaller while the picture still looks like the picture. Your browser decodes the image, redraws it at its original dimensions, and encodes it again as JPEG, PNG, or WebP at the quality you pick.

The result arrives next to the original with a drag-to-compare slider and the size difference in plain numbers, so you can see what a quality setting actually cost before you download anything.

You can also work the other way round and name the file size instead of the quality. Pick a limit — 100 KB, 200 KB, 500 KB, 1 MB, or a number of your own — and your browser tries descending qualities until the file comes in under it, then tells you exactly how many bytes it landed on.

It also takes a batch. Choose or drop a folder of photographs, set the format and the quality once, and every one of them is compressed here in turn — each with its own download, and all of them as one ZIP.

When to compress, and when to resize instead

Compress when the dimensions are already right and the file size is the problem: a phone photograph too large to email, a hero image slowing a page down, an upload form that refuses anything over a couple of megabytes.

If the image is also physically bigger than the space it is shown in, resize it first. Halving the width removes three quarters of the pixels, which usually saves more than any quality setting will, and Resize Image and Compress Image can run one after the other in Gizlet Flows.

What the format, quality, and target controls do

A format, and then one of two ways to say how hard to squeeze.

Output format

JPEG is the safe default for photographs and opens anywhere. WebP is usually noticeably smaller than JPEG at a comparable quality and every current browser supports it. PNG keeps every pixel exactly, which suits screenshots and flat graphics but makes a poor photograph format.

Quality

The default. The slider runs from 40% to 100% and starts at 82%, a good default for photographs. Below roughly 60% the artefacts start to show around hard edges and in flat areas like skies. It has no effect on PNG, which is lossless and has no quality to trade away.

Target file size

The other way round: name the limit and let the quality fall out of it. Your browser encodes the picture at descending qualities and keeps the first result at or under the limit, so the answer is a real measured file rather than an estimate. In this control KB means 1,000 bytes and MB means 1,000,000, because that is what an upload form asking for "under 500 KB" means. It is offered for JPEG and WebP; PNG has no quality to spend, so it stays on the slider and says so.

When the limit cannot be met

Some pictures will not come down that far at their current dimensions. Rather than switching format or shrinking the image behind your back, the Gizlet stops at the smallest attempt it made, says how many bytes over the limit that is, and offers it as a best attempt beside a link to Resize Image — because taking pixels out is the thing that works when quality has run out.

Several images at once

Up to 25 in one batch, all with the same settings. They are worked through one at a time rather than all at once, which is what keeps a tab responsive on a set of large photographs, and one file the browser cannot decode costs that one row rather than the batch. The comparison slider belongs to a single picture, so a batch shows a list of results instead.

Nothing to upload

The image is read, decoded, redrawn, and re-encoded by this browser, and the compressed file is handed straight to your downloads. Gizlet is a static site with no upload endpoint, so there is nowhere for a picture to be sent and nothing kept after you close the tab.

One side effect worth knowing: because the file is drawn onto a canvas and encoded fresh, the metadata the original carried does not come with it. Camera model, timestamps, and GPS coordinates are left behind in the source file.