V-Ray Tip: Efficient Motion Blur: Tune the Image Sampler Before Increasing Motion Subdivisions

Quick tip: optimize motion subdivisions to get cleaner motion blur at a fraction of the render time.

In modern V-Ray, motion blur quality is primarily governed by the image sampler. Treat “motion subdivisions” as a workflow: drive temporal quality with the image sampler first, then only raise geometry samples where truly necessary.

• Prioritize the image sampler
  • Start with a sensible Noise threshold: 0.02–0.03 for lookdev, 0.005–0.01 for finals.
  • Increase Max AA samples as motion streaks get longer or thinner: 64–128 is typical for aggressive action.
  • Leave legacy per-item subdivs at defaults; V-Ray’s unified sampler is more efficient at resolving MB noise.
• Use geometry/motion samples sparingly
  • Raise Geometry Samples only for fast deforming meshes (cloth, characters, cables) or very thin elements (wires, spokes, blades).
  • Typical range: 2–4 for most deformers; 6–8 for extreme motion or hair/fur. Avoid blanket increases across the scene.
  • For rigid objects, prefer Transform blur only; enable Deformation blur per-object when truly required.
• Balance shutter settings vs noise
  • Longer shutter = longer streaks = more samples needed. If you’re fighting noise, consider slightly reducing shutter duration instead of cranking samples.
  • Use shutter offset (center/leading/trailing) to control trail bias without inflating sampling costs.
• Tame hot highlights
  • Bright, blurred speculars can cause fireflies. Use Max Ray Intensity and/or Adaptive Clamping judiciously to stabilize highlights before raising samples.
  • Keep reflective/refractive trace depth appropriate; excessive depth amplifies MB noise in glossy materials.
• Leverage temporal denoising for animation
  • For sequences, V-Ray Denoiser with temporal mode can smooth MB noise across frames, allowing a higher noise threshold and lower Max AA samples.
  • Lock random seeds when necessary for consistent flicker-free results.
• Consider a hybrid approach in comp
  • For super-fast or tiny details, render a Velocity pass and use vector blur in compositing. This is often cleaner and faster than brute-force 3D MB.
  • Ensure correct velocity scale based on scene units and frame rate; test a short range before committing.
• Pipeline hygiene
  • Keep scene units and camera exposure physically consistent; mismatches exaggerate MB noise.
  • Profile with V-Ray logs and Render Elements (e.g., SampleRate) to see where the sampler spends time.
  • On GPU, favor raising Max AA and tuning Min Shading Rate instead of chasing per-effect controls.

Rule of thumb: increase image sampler quality first, then selectively add geometry samples on the few objects that truly need smoother deformation trails. Validate with short region renders around the fastest-moving edges before scaling up.

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