Round Corners

Round Corners does one thing: it takes an image, rounds its corners by whatever radius you choose, and gives you back a transparent PNG. The transparency is the important part. The corners are genuinely cut away rather than painted over, so the result sits correctly on any background rather than carrying a white or coloured triangle at each corner.

That is also why the output is always PNG. JPG has no alpha channel, so exporting a rounded image as JPG would have to fill the corners with something opaque, and the rounding would only look right on backgrounds of exactly that colour. PNG keeps the transparency and works everywhere it matters: the web, slide software, design tools and app store listings.

Choosing a radius is a matter of proportion rather than an absolute number. Twenty pixels reads as a gentle curve on a small tile and as almost nothing on a wide banner, so it is worth thinking in terms of a percentage of the width. Somewhere around 2 to 5 percent gives the modern rounded-card look; half the width of a square image gives a circle.

For circular avatars, crop to a square before rounding. A rectangular image with a very large radius becomes a pill or stadium shape rather than a circle, because the curve is limited by the shorter side, and that is rarely what people want when they set the radius to maximum.

One thing worth checking before you export: whether the place this image is going already rounds it for you. Many platforms round avatars and cards themselves, and pre-rounding an image that is then rounded again produces a visible double curve with an odd sliver of transparency between the two.

Everything happens in your browser on a canvas, so the image is never uploaded and the PNG is generated locally. That makes the tool usable for unreleased product shots, client mockups and anything else you would rather not hand to a third party.