Round Image Corners is a browser-based alternative for rounding the corners of a JPG, PNG, or WebP that runs entirely in your current tab without uploading the image to a server. The radius is set as a percentage from 1% to 50% of the image's shorter side, which keeps the curve predictable across landscape, portrait, and square sources — for a 400 by 200 pixel image, a 25% setting produces a 50 pixel corner radius. The output is a same-size PNG with transparent corners that preserves the source's original width and height, so the file is clipped to a rounded rectangle rather than resized or cropped. Because processing happens locally, you can repeat the export with different radii without re-uploading anything, and the result line reports source-matching dimensions, the computed whole-pixel radius, the output format, and the approximate file size. This positioning makes the tool useful as an alternative when CSS won't do (because it doesn't change the actual file), when a heavyweight desktop editor is overkill for one quick corner change, and when server-based online tools raise privacy or account concerns.
When CSS and design apps don't fit the rounding job
People land on the phrase "round image corners alternative" because the usual solutions don't always match the job. CSS border-radius is the first thing most web developers try, and it works well for live UI. The catch is that it only changes how the browser paints an element — it never touches the underlying image file. If you need a saved PNG with rounded corners to drop into a slide deck, an email template, a CMS media library, or a third-party form that doesn't run your stylesheet, the on-screen trick won't travel with the file. The corners disappear the moment the asset is exported, uploaded, or screenshotted.
Desktop editors like Photoshop, GIMP, and Affinity Photo handle the file correctly, but they are heavyweight for what is often a one-step task. You open the program, create a rounded-rectangle selection, mask or delete outside it, export as PNG, and close the program. Each step introduces a chance to flatten layers, lose metadata, change color profiles, or accidentally resize the canvas. For a quick social graphic, profile photo, or product card, that overhead can outweigh the result.
Server-based online tools are the most common alternative, and they do work, but they ask you to upload the image first. That means trusting a remote service with whatever file you happen to be rounding — a draft logo, an unpublished screenshot, a personal photo, a client mockup. Upload tools also tend to be vague about the radius they apply, often using a single fixed pixel value or a slider without explaining what the percentage maps to. When you need predictable, repeatable results across files of different shapes, that ambiguity becomes the bottleneck.
The slot that remains is a middle path: a file-based result, a predictable radius you can reason about in pixels, and processing that does not leave your machine. That is the role a local-browser rounding tool fills.
What a local-browser rounding tool changes
The defining shift with a local-browser approach is that the file is decoded, clipped, encoded, previewed, and downloaded inside the current browser tab. No upload step exists, so the source file is not transmitted anywhere. For a workflow built around client work, internal documentation, or unreleased designs, that single property is often the reason a person searches for an alternative in the first place. Round Image Corners follows this approach: it reads the chosen JPG, PNG, or WebP, creates a natural-size canvas, clears that canvas to transparency, defines a rounded-rectangle clipping path using the browser's canvas roundRect and clip APIs, draws the decoded source once at its original dimensions, and exports PNG.
The radius rule is the other thing that changes. Instead of asking for a pixel value that may or may not fit the file, the tool expresses the radius as a percentage of the image's shorter side. The shorter side is used deliberately so that the same percentage behaves the same way on a wide banner, a tall portrait, and a square avatar. The percentage is converted to a whole-pixel radius by rounding, and the canvas keeps the source's original width and height. There is no implicit rescaling, no cropped center, no decorative border, and no painted background behind the transparent corners — the output really is the source pixels with the area outside the rounded rectangle set to transparent.
The tool is also explicit about what it will accept. Inputs are JPG, PNG, or WebP files up to 25 MiB, and the decoded image must stay within a shared browser safety budget of 20,000 pixels per side and 40 megapixels total. Files that exceed those limits, decode failures, invalid radii, and failed PNG encodings surface as visible errors rather than silent partial downloads. That explicit-failure posture matters when the rounded result is going straight into a deliverable.
How to round image corners in your browser with Round Image Corners
This is the core task: take a local image and produce a same-size PNG with rounded corners, without leaving the browser. The tool is built around three actions, performed in order.
- Choose a local JPG, PNG, or WebP file that fits the displayed file size limit (25 MiB) and the per-side and total pixel budget.
- Set the radius using the control between 1% and 50% of the image's shorter side. Smaller values produce a subtle softening; higher values reach the largest valid rounded-rectangle radius the shorter side allows.
- Select Round corners, inspect the same-size PNG preview, and download the file. The download name ends in -rounded-corners.png, which makes the format change and transformation obvious in your downloads folder.
Three details make the workflow re-runnable without friction. First, changing the file or the radius invalidates the previous result, so a stale asynchronous export cannot overwrite a newer choice. Second, temporary Object URLs are revoked when they are replaced or when the tool closes, which keeps memory tidy across several rounds of edits. Third, you can change the radius and re-export without re-uploading anything, so trying 10%, 25%, and 40% on the same file costs no network round trips.
The result line below the preview reports the source-matching dimensions, the computed whole-pixel radius, the output format, and the approximate file size. Treat that line as a sanity check: if you loaded a 1920 by 1080 image and the result line shows 1920 by 1080, the file was not silently resized to fit a preview canvas.
How the shorter-side radius rule actually behaves
The percentage-to-pixels mapping is the part most alternative tools leave undocumented, so it is worth being explicit. A 1% setting on a 400 by 200 image means 1% of 200, the shorter side, which is 2 pixels. A 25% setting means 25% of 200, which is 50 pixels. A 50% setting means 50% of 200, which is 100 pixels — the largest valid rounded-rectangle radius for that shorter side. Rotate the file to 200 by 400 and the same percentages still resolve against the new shorter side (the 200 width), so a 25% setting on the portrait file also yields a 50 pixel radius.
Worked example for a 400 by 200 source image:
- Shorter side: 200 pixels
- Radius percentage: 25%
- Pixel radius calculation: 200 × 25 / 100 = 50
- Rounded to whole pixels: 50 pixels
- Output canvas: 400 × 200 (unchanged)
- Corner treatment: pixels outside the 50 pixel rounded rectangle become transparent
The same rule applied to a 1200 by 1600 portrait yields radius values that scale with the 1200 width — a 25% setting produces 300 pixels, and a 50% setting produces 600 pixels. A square source makes the rule even simpler, because both sides are the shorter side and the radius is symmetric in both directions. The behavior is the same regardless of shape, which is what makes the control reusable across mixed batches of files.
The table below compares this approach to the more common ways of rounding corners, using criteria that matter when choosing between methods.
| Criterion | CSS border-radius | Desktop editor | Server-based online tool | Round Image Corners |
|---|---|---|---|---|
| Touches the actual file | No — display only | Yes | Yes | Yes |
| Image leaves your machine | No | No | Yes, upload step | No |
| Radius expressed predictably | Per element, no file link | Per project, unit varies | Often vague or fixed | 1–50% of shorter side |
| Output dimensions vs source | N/A (no output) | May resize during export | May resize during export | Same width and height |
| Transparent corners supported | Yes (live only) | Yes (with PNG export) | Depends on tool | Yes (PNG output) |
| Account or sign-up required | No | No | Often yes | No |
What this alternative deliberately does not do
A fair evaluation of an alternative also requires naming what it is not. The tool is intentionally focused: it handles one image, one equal radius for all four corners, and produces one PNG. It does not offer separate radii per corner, masks you can edit, circular crops, decorative frames, shadows, gradients, batch processing, print color management, metadata retention, or lossless JPEG editing. If any of those are required, the right next step is a layered desktop editor rather than this browser tool.
The output format is also fixed at PNG, even when the source is a JPG. The reason is mechanical: JPEG cannot store transparent pixels, so the four corners that become transparent during the clip would be filled with an opaque color in a JPEG, which would defeat the whole operation. A JPG source is therefore decoded and re-encoded as PNG, which can increase the byte size of the output and means the original EXIF metadata is not preserved. The canvas-based export creates new PNG pixels rather than copying the source container, so camera info, GPS tags, and software tags do not carry over. Existing transparent pixels in a PNG or WebP source do remain available inside the clipped shape, because the canvas honors the decoded alpha.
Hard limits surface as errors rather than silent failures. Files above 25 MiB are rejected. Decoded images above 20,000 pixels per side or 40 megapixels total are rejected. Unsupported file types, empty files, decode failures, unavailable canvas support, invalid radius values, and failed PNG encoding all produce visible errors instead of a partial download. If the workflow can be described as "round the corners of this one image at one radius and hand me a PNG", the tool covers it. If it cannot, the limits above tell you quickly whether a different tool is needed.
If you also want to confirm that the local-browser processing claim holds up before loading a sensitive file, the safety walkthrough for Round Image Corners spells out exactly what to check, including where the decoding and encoding actually run.
If your reason for searching "round image corners alternative" is that CSS doesn't touch the file, a heavyweight editor is too much for the job, or server-based tools upload your image, a local-browser clipper fills that gap with a predictable shorter-side radius rule and a same-size PNG output. Pick the file, set the radius, and download — the rounded corners travel with the file rather than staying on a web page.
If you're weighing options, Base64 to Image Converter Alternative: Strict and Local covers this in detail.