Round the corners or crop into a circle, great for avatars, exporting transparent PNG.
Rounded corners soften images in cards, avatars and interfaces, and a circular crop is the standard for profile pictures. Two technical details make all the difference. The first is transparency: when you round a corner, whatever falls outside the curve has to become transparent, which requires a format with an alpha channel (PNG or WebP); JPG would fill the corners with a solid colour, so it is only offered once you set a solid background. The second is the circle: on a rectangular image, inscribing an ellipse produces a squashed oval, so the tool centre-crops the largest square first (or fits the whole image inside a square, if you prefer). Everything is processed in your browser with the Canvas API: the image is never sent to a server.
Every image is a rectangle. When you round a corner, what falls "outside" the curve does not vanish, it has to become transparent for the rectangle to look rounded. That transparency lives in the alpha channel, an extra piece of data per pixel that says how opaque it is. Formats like PNG (and WebP) store that channel; JPG does not, so on JPG the corners would appear filled with a solid color.
That is why the tool always outputs PNG: it is the most compatible format that preserves the transparent edges in any destination, sites, apps, editors and documents. If you do not need transparency, you can choose a solid background color, and then the corners are filled with the chosen color instead of being cut out.
Example 1, a profile avatar: pick the Circle mode. If the photo is not square, the tool automatically centre-crops the largest square, so the result is a true circle, not the squashed oval you get from editors that simply inscribe an ellipse in the rectangle. The resulting transparent PNG drops onto any background.
Example 2, a card thumbnail: choose Rounded corners and adjust the radius to match your layout (a small radius is discreet; a large one looks very "soft"). Export with a transparent background to place it over any color, or with a solid background if the destination does not accept transparency.
If the image will appear on a site you control, it is often better to round it with CSS border-radius: the file stays rectangular (smaller and reusable) and the browser draws the curve. Rounding directly in the image makes sense when the destination does not allow CSS, a platform's avatar upload, a document, a slide, an email, or a thumbnail that must come ready-made.
The edges come out smooth because Canvas draws the rounded mask with anti-aliasing, blending the edge pixels into the transparency instead of leaving a jagged step. Just remember that baking the rounding into the image is permanent: keep the original in case you need a different radius later.
Paste the code into your HTML and the tool shows up on your page, without J-Kit's navigation and ads. It still runs in the browser of whoever visits your site.
<iframe
src="https://jkit.tools/embed/en-US/round-image-corners"
width="100%"
height="600"
style="border:0"
loading="lazy"
title="Round Image Corners"
></iframe>If the background is transparent, the output needs an alpha channel: PNG (the most compatible) or WebP. JPG cannot store transparency, so it is not even offered in that case. If you chose a solid background colour, there is no transparency to preserve and JPG produces a much smaller file.
Rounding happens entirely in your browser. No image is sent to any server.