Add Motion Blur to a PNG

length and angle · alpha-correct averaging · batch · nothing uploaded

Directional blur smears an image along one axis, the way a camera does when the subject moves during the exposure. Unlike a regular blur, which softens everything equally, this gives a clear sense of direction and speed.

Length, angle, and what they mean

Length is how far each pixel is smeared, in pixels, and it reads directly as speed — 8 px is a slight camera shake, 30 px is a moving car, 100 px+ is an abstract streak. Scale it with your image: 24 px on a 400-pixel-wide image is a heavy blur, while on a 4000-pixel-wide one it's barely visible.

Angle is the direction of travel. 0° is horizontal, 90° vertical, 45° diagonal. The blur is symmetrical about each pixel — it extends equally in both directions along the axis — so 0° and 180° produce the same result. That symmetry is what real motion blur looks like when the whole frame is moving.

The transparency detail

Averaging colours near a transparent edge is where naive implementations go wrong: they pull the colour of invisible pixels into the visible ones and leave a dark or grey halo around a cut-out subject. This averages in premultiplied space — each pixel's colour is weighted by its own alpha before summing, and the total is divided by the accumulated alpha rather than the sample count. A cut-out object blurs into clean transparency with no fringe.

Where it works, and where it doesn't

Blurring the whole frame reads as camera movement — a handheld pan, a shaky shot. That's a real and useful look for backgrounds, title cards and abstract textures. What it can't do is blur only the moving subject while the background stays sharp, which is what a photograph of a passing car actually looks like. That needs a mask, and masking needs a real editor.

A workable approximation: motion-blur a copy of the whole image, then use Overlay images to composite the sharp original back over the middle. For non-directional softening, Blur is the tool; for the opposite, Sharpen; and Zoom plus a blur approximates a zoom-burst.

FAQ