How to Blur an Image Online — Free (2026)

You can blur any image online for free using brevio Image Blur. The tool runs a box blur directly on pixel data in your browser — no upload, no server, no watermark.

How to Blur an Image Online

1. Open brevio Image Blur. No sign-up or account needed.
2. Drop your image or click to choose a file. Accepted formats include JPG, PNG, and WebP. The file stays in your browser.
3. Adjust the blur radius. Use the slider to set a radius from 1px (subtle softening) to 20px (heavy blur). The preview updates live.
4. Download the result. Click "Download PNG" to save the blurred image.

How box blur works

A box blur replaces each pixel with the average colour of all pixels within a square neighbourhood. For a radius of r, the neighbourhood is a (2r+1)×(2r+1) square centred on the pixel. At r=5, each output pixel is the average of 121 input pixels. Pixels near the edge use clamped coordinates — the nearest in-bounds pixel is repeated — so the edge does not produce artefacts.

Box blur is computationally simple but not identical to Gaussian blur, which weights central pixels more strongly and produces a rounder, more natural-looking softening. At small radii the difference is minimal. For professional photo editing, Gaussian blur is preferred; for privacy masking and UI prototyping, box blur at radius 8–15 is more than sufficient.

Common uses for image blurring

• Privacy masking: Blur faces, licence plates, or sensitive information before sharing a screenshot or photo publicly.
• Background softening: Apply blur to a background layer to create a depth-of-field effect in a composite image.
• UI design: Blurred images are commonly used as hero backgrounds behind overlaid text.
• Noise reduction: A small blur radius (1–3px) smooths compression artefacts in JPEG images.
• Thumbnail generation: Blurred thumbnails are used as low-quality image placeholders (LQIP) while the full image loads.

Performance considerations for large images

Box blur at large radii is O(r²) per pixel, so a 4000×3000px image at radius 20 processes roughly 2.4 billion multiply-add operations in the browser's main thread. On modern hardware this takes 2–5 seconds. For production use with large images, consider a separable blur (two 1D passes instead of one 2D pass) or offload to a canvas worker. This tool uses a straightforward 2D pass that is adequate for most images under 2000×2000px.

Frequently Asked Questions

What is the maximum blur radius?

This tool supports radii from 1 to 20 pixels. A radius of 20 is a very heavy blur — at that level individual features are typically unrecognisable. For a subtler softening effect, 2–5px is usually sufficient.

Does blur reduce file size?

Yes, noticeably. Blurring reduces high-frequency detail, which compresses more efficiently. A blurred JPEG or WebP will be significantly smaller than the original at the same quality setting. This tool outputs PNG (lossless), so file size reduction is less dramatic — use a format converter after blurring if size matters.

Can I blur only part of an image?

This tool applies blur to the entire image. For selective blurring (e.g., just a face), use an image editor such as GIMP, Photoshop, or Canva, which support layer masks and selection-based blur.

Is my image uploaded anywhere?

No. Processing runs entirely in your browser using the HTML Canvas API. The image data never leaves your device.