Vector Motion Blur

Synthesize motion blur by smearing an image along a per-pixel flow vector field — the classic flow-based application of Optical Flow.

Category: Effects Menu path: Effects > Vector Motion Blur

This is distinct from the layer-level Motion Blur toggle — that one does temporal supersampling during rendering (shutter simulation on animated content). Vector Motion Blur applies in 2D image space using an externally-computed flow field, useful for footage that was captured without sufficient motion blur.

Ports

Port	Type	Direction	Description
in	imageRgba16f	input	Color image to blur
flow_in	imageRgba16f	input	Flow field (typically OpticalFlow.out). R=u, G=v in fractional UV per frame.
out	imageRgba16f	output	Motion-blurred image

Parameters

Param	Type	Default	Description
strength	scalar	1.0	Flow magnitude multiplier. 1.0 = use flow as-is; 2.0 = doubled motion blur; 0.5 = half.
phase	scalar	0.0	Blur window position along the flow. −1 = leading (blur in front of pixel), 0 = centered (standard 180° shutter look), +1 = trailing (blur behind pixel — "afterimage"). Clamped to [−1, 1].
samples	scalar	16	Samples along the blur axis. More = smoother, quadratically more GPU cost. Clamped 1-64.

How It Works

For each output pixel, Vector Motion Blur:

1. Reads the flow vector at the current UV from flow_in.rg.
2. Multiplies it by strength to get a world-space motion vector.
3. Samples in at samples points distributed along that motion vector (spanning [-0.5 + phase*0.5, 0.5 + phase*0.5] of the flow magnitude).
4. Averages the samples.

Result: pixels smear along the direction they moved. Fast-moving areas get heavy blur; stationary areas stay crisp. Matches how real-world motion blur looks.

The phase param controls whether the blur trails behind the motion (like a camera shutter that opens late — leaves an afterimage), leads ahead of it (opens early — ghostly anticipation), or is symmetric (standard photographic motion blur).

Usage Examples

Standard motion blur on video footage

VideoSource ──► OpticalFlow ──► flow_in
VideoSource ──────────────────► in  ──► VectorMotionBlur (strength: 1.0, phase: 0) → Output

Classic application — video with insufficient natural motion blur gets synthesized blur. Default strength=1.0 gives "as-captured" motion amount; bump to 2.0-3.0 for a dreamier look, or down to 0.3-0.5 for subtle smoothing.

Exaggerated motion for stylized shots

Raise strength to 3-5 for streak-style motion. Good for sports highlights, action sequences, music video beats.

Leading/trailing afterimage effect

phase = 1.0 gives a trailing blur that looks like a photographic afterimage or a slow-shutter shot — often used in dance/performance footage.

Motion-driven brushstroke effect

Apply to a still image with an artificially-constructed flow (e.g. Noise.vectorField → ImageSample → VectorMotionBlur) to get a painterly directional blur without needing video.

Partial blur via mask

Not built-in, but achievable via Mix: VectorMotionBlur → Mix (mask: alpha mask) ← Source. Areas in mask get blurred; areas outside stay crisp.

Tips

• Pair with OpticalFlow smoothness tuning: if the blur looks jittery, the source flow is too noisy. Raise OpticalFlow's smoothness to 20-50.
• Samples vs strength tradeoff: high strength needs more samples to look smooth. Streaked look at 5× strength: bump samples to 32-64.
• Phase for temporal feel: centered phase looks "natural"; trailing phase feels slower/more languid; leading phase feels anxious/anticipatory. Match to the shot's emotional tone.
• Zero-motion areas are crisp automatically: pixels where flow is zero get no blur, so static elements in otherwise-moving footage retain sharpness.
• Strength below 1.0 is valid: useful for "took too much motion blur naturally, want to reduce it" — can't fully undo, but the apparent motion softens.

Related Nodes

• OpticalFlow — the canonical flow source
• Blur — isotropic blur without direction
• UVRemap — another flow consumer, but for displacement rather than integration
• ChromaticAberration — another per-pixel directional effect
• Mix — blend blurred + original for partial strength