Compress images, right in your browser.

How image compression works — and how to keep it invisible

Compression makes a file smaller in one of two ways: by storing the same pixels more cleverly, or by dropping detail your eye was never going to catch. Knowing which one is happening matters, because the first is free and the second has a cost. This tool gives you two knobs — a format and a quality level — and both run in your browser, so you can nudge them and watch the size change without anything being uploaded.

Lossy vs lossless: what actually gets thrown away

Lossless compression rewrites the file so the same pixels take fewer bytes; nothing is discarded, and the image opens bit-for-bit identical. That is how PNG is optimised here, and the savings are real but modest — often 5–25%. Lossy compression — the JPEG, WebP and AVIF path — is where the big drops come from: it discards the detail you are least likely to notice, such as subtle gradients and fine noise, which is why 50–80% is normal. Every lossy save throws away a little more, so always compress from the original, not a copy that was already compressed. When you cannot afford any change at all — line art, a screenshot full of text — turn on the Lossless toggle, which appears for PNG and Keep.

What quality level should you pick?

The quality slider runs from 10 to 100 and starts at 80. Higher keeps more detail and makes a bigger file; lower does the opposite. There is no single right number — it depends on what the image is:

• Photographs — 80–85 is the sweet spot, visually hard to tell from the original at a fraction of the size.
• Screenshots, logos, text and flat UI — stay at 90+ or use a lossless format; low quality smears crisp edges into visible fringes.
• Thumbnails and small previews — 60–70 is plenty, since nobody zooms into a 200-pixel image.
• Below 50 — only when hitting a size limit matters more than a little blockiness.

Because moving the slider re-runs every image straight away, the fastest way to find the edge is to drag the quality down until a difference just shows, then step back one notch.

Format matters more than the quality slider

The biggest lever is often the format, not the number beside it. At the same visible quality, WebP is typically 25–35% smaller than JPEG, and AVIF is usually smaller still. The reverse holds too: a photo saved as PNG can be several times larger than the same photo as WebP, because PNG is built for flat graphics, not continuous-tone photos. Keep leaves the format untouched; pick a specific one to convert while you compress. For the smallest file, switch to WebP or AVIF instead of squeezing the quality slider on an old JPEG or PNG. The convert tool is the same engine with the format choice up front, and the PNG to WebP guide shows the size gap on real files.

Compressing a whole batch

Drop a folder and every image is compressed with the same format and quality, then handed back as a single zip — a whole blog post's photos in one pass. Because one setting applies to all of them, group images that want the same treatment: run the photos at 80 in one pass and the screenshots at 95 in another, rather than forcing one number onto both. Nothing is uploaded, so a 200-image batch runs on your own machine, limited only by memory rather than a server quota or a daily cap.

When compression won't help

Some files have little left to give. A JPEG already saved at quality 80 gains almost nothing from being re-compressed at 80, and can pick up fresh artefacts in the process — the savings badge shows a +% when a file actually grows instead of shrinks. Tiny images such as icons or 200-pixel thumbnails are already near their floor. And the most common reason a "compressed" file is still heavy is not compression but dimensions: a 6000-pixel phone photo squeezed in bytes is still a 6000-pixel photo. If the pixel count is far larger than the size it is shown at, resize it to the width you actually use — around 1600px covers most web layouts — and then compress. Resizing is the bigger win whenever an image runs far larger than it needs to.

For the full workflow of trimming a heavy image down, read how to reduce image file size; to keep every pixel intact, see compress without losing quality.