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About this tool
Rounded corners are a small visual detail with an outsized effect on how people read your product. Mobile interfaces, card layouts, and social feeds have trained audiences to associate gentle fillets with polish, while sharp ninety-degree edges can feel utilitarian or unfinished. SynthQuery’s Round Corners Tool is a free, browser-based image corner rounder—identified as RESIZE-046 in our catalog—that keeps every decode, clip, preview, and download inside your tab: nothing is uploaded to SynthQuery for this workflow. You can drag in JPG, PNG, WebP, BMP, or TIFF sources, build a batch queue, and export PNG with transparent pixels outside the rounded silhouette (or JPEG flattened against a matte you choose). Sliders express radius as a percentage of the image’s shortest side—up to fifty percent per corner before geometric clamping—so a wide banner and a square icon both get predictable, proportional curves. Uniform mode sets all four corners together; advanced mode unlocks independent top-left, top-right, bottom-right, and bottom-left radii for asymmetric cards, chat bubbles, and editorial shapes. Presets jump to slight (five percent), medium (fifteen percent), large (twenty-five percent), and pill (fifty percent of the short side) so you can iterate quickly before fine-tuning. The live preview sits on a checkerboard so transparent corners are obvious even when your final export uses a solid brand background. When you are done, download one file or ZIP the whole queue. Pair visuals with SynthQuery’s free-tools hub at /free-tools and the full directory at https://synthquery.com/tools; for copy governance beside your graphics, route text through the AI Detector or Humanizer when policies require it.
Modern UI, app icons, and social presentation
Product designers mock buttons and tiles as bitmaps when handoffs must be PNG attachments. App teams prepare square marketing masters before engineering applies platform-specific masks—iOS and Android each have nuanced icon geometry, but a circular fillet at a known percentage is still the fastest way to align stakeholder previews. Social managers soften thumbnails that will sit inside rounded containers in schedulers that ignore CSS. Presentation authors flatten headshots for slide masters that forbid live styles. This tool targets those raster-first workflows where CSS border-radius cannot travel with the file.
Transparency, alpha, and the checkerboard convention
PNG sources retain interior semi-transparency through decode; clipping removes only pixels outside the rounded path. JPEG sources have no alpha—transparent background mode still produces clear exterior pixels in PNG exports, which helps when you will composite again. The checkerboard pattern is a universal cue for emptiness: SynthQuery’s preview always renders transparent outer corners for clarity, while your download respects the Background and format controls you selected.
Client-side limits and privacy
Large camera rasters are constrained by the same longest-edge guards used in sibling SynthQuery imaging utilities so canvases stay responsive. File type and size checks run before decode, with inline errors for corrupt TIFFs or truncated downloads. Queue caps prevent accidental hundred-file drags from freezing modest laptops. The documented pipeline does not transmit your bitmap bytes to our servers for rounding—exports are a deterministic function of local files and slider positions.
What this tool does
The interface follows the established SynthQuery image-utility rhythm: enqueue files, select a row for inspection, adjust controls while the preview regenerates, then download individually or as a ZIP. Corner radius uses a zero-to-one-hundred slider whose maximum equals fifty percent of the shorter side of the output bitmap—the largest circular quadrant that still fits along both axes before the engine scales adjacent corners that would otherwise overlap on extreme aspect ratios. A toggle locks all four corners to one value or exposes separate sliders for top-left, top-right, bottom-right, and bottom-left when you need only the top edge softened or a bubble shape with one sharp corner. Presets encode common marketing steps: slight for light polish on dense grids, medium as a balanced default for hero stills, large when the curve should read clearly at small thumbnails, and pill when the short axis should approach semicircular ends. Background mode selects transparent export (ideal for layered comps), solid white, solid black, or a custom hex sampled from your design system. Download format switches between PNG, which preserves alpha outside the clip when transparent mode is active, and JPEG, which always flattens against the matte color because the JPEG codec cannot store transparency. Batch mode lists each file with decode status and packages successful rows into one archive with predictable “-round-corners” suffixes. Accessibility follows patterns from other tools: labeled sliders, switches, and selects; descriptive preview names; keyboard focus order without traps.
Uniform versus per-corner control
Uniform mode is fastest for avatars, tile grids, and iconography where symmetry is assumed. Disabling the switch keeps your current numeric values and reveals four sliders—useful for navigation headers, partial rounding along one edge, or playful editorial layouts. Returning to uniform averages the four corners so the transition does not jump to an arbitrary default.
Presets mapped to percent of the short side
Slight applies about five percent of the shortest dimension as the fillet radius—enough to soften without dominating. Medium targets fifteen percent for general marketing thumbnails. Large uses twenty-five percent when the curve must read on small screens. Pill drives toward the fifty percent ceiling so the short axis behaves like a stadium shape. Touching any slider marks the preset dropdown as Custom until you pick a preset again.
Batch ZIP and naming
Add many files via the picker or a single drop; the queue shows spinners while decodes finish. Download Selected writes one output; ZIP All walks every ready row. Duplicate filenames in one batch receive numeric prefixes so archives unpack cleanly on every operating system.
Technical details
Implementation builds a closed Canvas 2D path that traces a rounded rectangle. Each vertex uses arcTo (or the native roundRect helper when available) so fillets are true circular quadrants after radii clamp to prevent edge overlap. The path is applied with clip() before drawImage scales the decoded bitmap into the working surface, discarding samples outside the silhouette while preserving interior alpha. This mirrors the mental model of CSS border-radius on a replaced element, except the output is a flattened raster. Anti-aliasing along the curve is handled by the browser’s rasterizer; semi-transparent edge pixels blend against clear or solid fills depending on background mode. JPEG export fills the canvas with the selected matte first because lossy encoding has no alpha channel. Preview generation uses transparent exterior pixels on a checkerboard container so you always see the cut corners; export still follows your Background and format selections.
Why arcTo instead of hand-tuned quadratics
Quadratic curves per corner can drift from a true circular arc unless control points are derived carefully. arcTo intersects edge tangents and emits a circular arc with an explicit radius, which stays stable as sliders approach the maximum. When roundRect with per-corner radii exists, the engine normalizes internally; the fallback path keeps older evergreen browsers aligned.
Alpha through the clip
Transparent background mode clears the framebuffer, applies the clip, then draws the image—exterior pixels remain fully transparent. Clipping does not premultiply unless a subsequent flatten step does. Solid fills paint the full rectangle first, then the image sits inside the same clip for consistent edges.
Use cases
App icon designers prepare square PNG masters with visible rounding before handing assets to Xcode or Android Studio, then finish platform packs with the App Icon Generator when pixel-accurate folders are required. UI and UX teams export card imagery for legacy CMS fields that only accept uploads, not inline CSS. Social media producers soften graphics that will be re-cropped inside rounded frames in native apps. Ecommerce stylists round product cutouts that will sit in email modules with fixed corner radii. HR and internal comms teams batch-process directory avatars. Teachers demonstrate bitmap clipping without installing lab software. Presentation specialists flatten rounded headshots for PowerPoint and Keynote templates that lock aspect ratio. Photographers deliver client-friendly PNGs with transparent corners for compositing in InDesign or Figma. Agencies processing dozens of logos in a sprint rely on ZIP export to keep deliverables consistent.
App icon standards (iOS and Android)
Apple’s production icons use a superellipse mask, not a pure circular fillet; Google’s adaptive icons layer foreground and background shapes. This tool produces raster fillets at explicit percentages—excellent for marketing previews and early mocks. For store submission, still follow each vendor’s official template and use SynthQuery’s App Icon Generator for full size ladders rather than relying on a single rounded square alone.
Social and presentation graphics
When schedulers flatten everything to bitmaps, pre-rounded PNGs survive downstream crops more predictably than sharp squares that networks re-mask aggressively. For slides, match matte colors to slide backgrounds when you must use JPEG; otherwise PNG with transparency keeps flexibility for template changes.
Product photos and UI mockups
Combine rounded exports with Drop Shadow or Transparent Background when you need lifted cards or clean silhouettes. If copy in the same deck was drafted with AI assistance, run prose through the AI Detector where disclosure policies apply.
How SynthQuery compares
CSS border-radius is ideal when you control HTML and only need on-screen presentation: resolution independent, easy to tweak in devtools, and animatable. It does not attach a file suitable for email, marketplace uploads, PDF embeds, or chat clients that rasterize attachments. Cloud editors often round corners too, but many require uploads and accounts. Desktop suites offer non-destructive vector workflows at higher licensing and onboarding cost. SynthQuery focuses on fast, private, flattened raster output with per-corner control, percent-based radii tied to the short side, batch ZIP packaging, explicit PNG versus JPEG choice, and a checkerboard-backed preview—free in the browser without sending your pixels through our servers for the documented workflow.
| Aspect | SynthQuery | Typical alternatives |
|---|---|---|
| Deliverable | Flattened PNG (transparent corners) or JPEG with user matte—ready for any channel that accepts bitmaps. | CSS rounds live DOM nodes but does not produce an attachment; design apps export with heavier workflows. |
| Radius semantics | Sliders map to percent of shortest side (0–50% max per corner before pair clamping). | Some editors use absolute pixels only, which scales poorly across mixed-size batches. |
| Privacy posture | Decode and clip locally in the tab for the workflow described on this page. | Remote processors may store uploads—read terms before sending sensitive brand assets. |
| Batch asymmetry | One setting set applies to every queued image; ZIP bundles all successful encodes. | Lightweight web toys often lack batch or per-corner independence. |
How to use this tool effectively
Follow these steps whenever you need rounded raster assets and want the work to stay on your machine.
Step 1: Add images
Click Browse or drag files into the dashed drop zone. JPG, PNG, WebP, BMP, and TIFF are accepted up to the per-file size limit on the page. Multiple files enqueue; each row shows a spinner while decoding. Click a row to drive the preview pane.
Step 2: Choose uniform or per-corner mode
Leave “Same radius on all corners” enabled for symmetrical tiles and avatars. Turn it off to adjust top-left, top-right, bottom-right, and bottom-left independently—ideal when only one edge should soften or when mimicking directional bubbles.
Step 3: Set radius with sliders or presets
Drag the master slider from zero to one hundred, remembering that one hundred equals the maximum semicircular fillet along the short axis (fifty percent of that side as radius). Alternatively open the preset menu for slight, medium, large, or pill. Manual slider changes mark the preset as Custom.
Step 4: Configure background and format
Pick Transparent for PNG exports with clear exterior pixels, or White, Black, or Custom when the destination forbids alpha. Choose PNG for lossless edges and transparency, or JPEG for smaller attachments. JPEG always uses the matte color you select.
Step 5: Review the live preview
The preview always shows transparent outer corners on a checkerboard so you can judge the curve even if you will export on a solid color. Wait for spinners on large TIFFs; zoom the browser if you need to inspect anti-aliasing.
Step 6: Download or ZIP
Download Selected saves the active row. ZIP All packages every successfully decoded image with disambiguated names when duplicates exist. Clear All revokes object URLs to free memory when you start a new batch.
More SynthQuery tools
- Circle Crop
Crop to a circular mask with transparent or solid backgrounds before or instead of corner fillets.
- Image Resizer
Set exact width and height—including square outputs—after you finalize corner geometry.
- Brightness & photo adjustments
Tune exposure and pair with Contrast, Saturation, Gaussian Blur, and other utilities on the free-tools hub.
- Background Remover
Replace or remove backgrounds so rounded clips hug the real subject instead of a rectangular matte.
- App Icon Generator
Export iOS, Android, Windows, and macOS size ladders with platform-appropriate masks when mocks become production.
- Transparent Background Maker
Remove solid-color mats before rounding so curves follow the subject silhouette.
- Drop Shadow Creator
Lift rounded cutouts from flat surfaces with adjustable blur, offset, and color.
- Free tools hub
Browse calculators, croppers, and editors; https://synthquery.com/tools lists the full catalog.
Frequently asked questions
Each slider runs from zero to one hundred. The tool converts that to a pixel radius proportional to the shortest side of the output bitmap: one hundred means the radius reaches fifty percent of that short side—the largest symmetric circular fillet that still fits before the engine scales corners that would overlap on very wide or tall images. Smaller images therefore get smaller pixel radii than larger images at the same slider position, which keeps the visual weight consistent across a heterogeneous batch.