Blur & Sharpen

Soften a picture, from a gentle defocus to fast streaks of motion, or make soft footage crisper. Add one in Properties → Effects → + Add Effect (Using effects).

Box BlurAverages a square around every pixel: a graphic softness in which small lights turn into flat squares.
Gaussian BlurA smooth, even softening, like a lens out of focus.
Motion BlurSmears the picture in one direction, as if the camera or the subject moved fast while the shutter was open.
Radial BlurBlurs the picture around a centre point: Zoom streaks it outward from the middle, Spin turns it in circles.
Zoom BlurStreaks the picture outward from a centre point, as if the camera rushed in while the shutter was open.
SharpenBrings out detail and crisp edges in soft footage, without the thick bright and dark outlines of strong sharpening.

Which one?

I want…	Use
a natural, out-of-focus softness	Gaussian Blur
a graphic softness with square lights	Box Blur
streaks of movement in one direction	Motion Blur
a swirl or a soft rush towards one point	Radial Blur
a strong, even zoom burst	Zoom Blur
crisper detail	Sharpen

Two street lamps of the night street, enlarged: Gaussian Blur at Radius 10 makes soft round glows, Box Blur at Radius 10 flat, blocky squares — The same street lamps, enlarged (Radius 10): Gaussian Blur makes soft round glows, Box Blur flat, blocky squares.

The shared idea

All five blurs follow one recipe: weigh each colour by its transparency (Premultiplied Source), read neighbouring pixels (Sample Image), weigh each read, add them up and divide by the total weight (Sequence Reduce, Normalize by Weight), then restore normal transparency (Straight Alpha Output). That is why transparent edges (logos, titles, keyed footage) fade out cleanly, without a dark rim.

Gaussian and Box Blur do this along the rows, then along the columns. They differ only in the weight of each read.
Motion, Radial and Zoom Blur do it along a path, in short pieces first.
Sharpen blurs a copy with Gaussian Blur’s passes and adds the difference back.

How to open a graph: The node setup.

Technical details

Radius is measured on a 1080p frame and scales with the picture, so the preview, the export and 4K show the same softness. Transparent edges blur without a dark rim. A blur at 0 leaves the picture exactly as it was.

Where the editor falls back to its software preview (no WebGPU, for example on some Linux drivers), Motion, Radial and Zoom Blur are painted on the CPU, pixel by pixel, with the same path as the GPU. That path keeps its reads in reused number lists instead of building new ones for every read, so a frame paints about five times faster than in the first smooth version; a test holds it within a budget measured against a plain pass on the same machine.

Developer notes: Effect system: Blur & Sharpen notes.