V-Ray Tip: VRayDirt Radius Calibration for Scale‑Accurate Ambient Occlusion

Fine-tune VRayDirt’s Radius to control the spread and character of ambient occlusion for grounded contact shadows without muddying your materials. If you need licenses or upgrades, check NOVEDGE.

Why the Radius matters

• Radius defines how far VRayDirt looks for nearby geometry to occlude. Too small and details vanish; too large and you’ll get a gray wash over broad surfaces.
• Distribution shapes the falloff across that radius. It’s your “contrast” control for how quickly occlusion fades from creases to flats.
• Scene scale is critical. Always choose values in real-world units consistent with your model.

Scale-aware starting points

• Products/jewelry: Radius 0.2–2 mm; Distribution 1.0–1.5 for crisp micro-contact.
• Furniture/props: Radius 2–15 mm; Distribution ~1.0 for balanced edge darkening.
• Interiors/architecture: Radius 2–25 cm; Distribution 0.8–1.2 to avoid “dirty” walls.

Fast calibration workflow

• Measure a representative gap (panel seam, tile grout, baseboard offset). Set Radius close to that physical distance.
• Start Distribution at 1.0. Increase above 1.0 to tighten darkness toward creases; drop below 1.0 for broader, softer spread.
• Use Render Region in the VFB and toggle IPR to iterate quickly. Keep an eye on midtones; avoid flattening albedo.

Clean, controllable results

• Blend short and long radii: Layer two VRayDirt nodes (tight + broad) via a Composite/Blend to capture both crevice depth and gentle contact. Keep each layer subtle.
• Restrict scope with Consider same object only when you want self-occlusion without cross-object bleed (useful on dense kitbashes).
• Enable Work with transparency so cutouts (foliage, grilles, decals) participate correctly.
• Invert normals to switch between outside edge shading and cavity-only grime for material-driven looks.
• Map the Radius slot: drive size by vertex color, curvature, or a procedural to add variation (e.g., larger radius near ground via VRayDistanceTex).

In the pipeline

• Non-destructive comp: Add a VRayExtraTex render element with VRayDirt to export an AO pass. In comp, multiply at 10–30% and mask by materials to avoid over-darkening bright surfaces.
• Reflections: In “reflection occlusion” mode, a modest radius can tame overly bright glossy corners without crushing diffuse.
• Performance: Larger radii trace farther and cost more. Use the smallest radius that achieves visible grounding; larger values explode render time with diminishing returns.

Common pitfalls

• Global gray wash: Your Radius is too large or Distribution too low. Reduce Radius first.
• Patchy noise: Raise overall sampler quality (Noise Threshold) rather than chasing legacy per-map subdivs in modern V-Ray.
• Scale mismatch: If switching units or importing assets, recalibrate Radius to the new scene scale.

Pro tip: Author “material AO” inside a VRayBlendMtl. Use a tight-radius VRayDirt as a mask to mix a slightly darker, rougher layer only in crevices. It enhances realism while preserving physically based lighting. For licensing, upgrades, and expert advice, visit NOVEDGE or explore bundles at NOVEDGE.