Set a corner radius, pick which corners, save a PNG with clear corners. Runs on your device.
You can enter the radius in pixels or as a percent of the image's shorter side. Percent is the better choice for a batch: 10 percent rounds a 400 by 300 thumbnail and a 4000 by 3000 photo by the same visible amount, while 40 pixels would barely show on the large one. The radius is always held to half of the shorter side, because a larger one would make opposite curves overlap. On a 400 by 300 image the most you can get is 150 pixels, and 50 percent means the same thing. The result is rounded to whole pixels. The preview shows the first image smaller than the saved file and scales the radius with it, so what you see matches the saved proportions.
The corners that are cut away have to show something. With Transparent, they are left clear, and the file is saved as PNG for every source, because PNG holds transparency. JPEG cannot, so a JPEG you add comes out as a PNG, which is usually larger than the original. If you need to stay in JPEG, switch Corner fill to Background colour and choose a colour, for example white to match a page. The corners are then filled with it, a JPEG stays a JPEG saved at quality 92, and PNG and WebP images are saved as PNG. A PNG or WebP that already has see-through areas shows the background colour there too in this mode. The saved picture is drawn once, clipped to the rounded outline.
All four corners are on by default. Untick any to keep them square, for example to round only the top corners of a banner that sits on a card. At least one corner must be ticked, and the page says so when none is. The saved image has the same width and height as the original, unless it is larger than your device's canvas allows, in which case it is made smaller and the result shows both sizes. Nothing is cropped away except the corner pieces. A phone photo's rotation flag is applied first, so a portrait photo stays upright, and the camera and location details stored in the original are not copied into the saved file.
It rounds rectangles only. It does not cut an image to a circle or an oval, which is a crop and belongs to the circle crop page of the crop image tool. It does not add a border, a shadow or a frame, and it does not soften or feather the edge: the edge is the anti-aliased curve the browser draws. It also does not change the pixel size or compress the file. Use the resize and compress tools for that. Because the corners are removed from the picture itself, you cannot restore them from the saved file, so keep the original.
JPEG cannot store transparent pixels, and clear corners need them. With Corner fill set to Transparent, every image is saved as PNG. To keep JPEG, choose Background colour: the corners are filled with that colour and a JPEG is saved again as a JPEG at quality 92.
There is no single right number, so judge it in the preview. Around 10 to 20 percent of the shorter side gives a clearly rounded square, and 2 to 5 percent gives a slight softening. Percent keeps the same look across images of different sizes.
Yes. Untick Bottom left and Bottom right under Corners to round. The preview updates at once. The two unticked corners stay square, and the radius applies to the ticked ones only.
With percent, the proportion is the same, so the pixel radius differs with each image's shorter side. With pixels, every image gets the same number of pixels, held to half of its own shorter side. A batch can be up to 50 images, saved in one .zip.
Setting 50 percent on a square image gives the most rounding possible, which looks like a circle, but the file stays a full-size square with clear corners. To cut the picture to a circle, use the circle crop page of the crop image tool.