ZBrush Tip: Mask by Smoothness for Precise Edge Control and Polygroups

Quickly isolate crisp edges and accent lines with Mask by Smoothness to control polish, creasing, and detailing with precision.

What it does: analyzes local curvature to detect and mask sharp ridges or, inversely, broad smooth areas. It’s ideal for protecting bevels while smoothing panels, targeting edge highlights for polypainting, or tightening silhouettes without destroying nearby form.

• Where: Tool > Masking > Mask by Smoothness (adjust the intensity, then click to apply). Repeat to strengthen the selection.
• Best density: works reliably when your sculpt has clean, mid-to-high resolution surface continuity (avoid extremely noisy Dynamesh states).
• Invert on demand: Ctrl+click on the canvas to invert, choosing whether you affect ridges or the flats around them.

Core workflows:

• Sharpen edges safely
  • Run Mask by Smoothness to select ridges.
  • Invert if needed so only the ridge line is unmasked.
  • Use Pinch, HPolish, or Deformation > Polish by Features at low values to tighten without stair-stepping.
• Protect panel lines while smoothing
  • Keep ridges masked and run Smooth, Polish, or TrimDynamic on the surrounding surfaces.
  • Result: flatter planes with crisp seams intact—great for hard-surface concepts and kitbashing.
• Make production-friendly selections
  • After masking, Tool > Polygroup > Group Masked to convert edges into discrete Polygroups.
  • Use Crease PG before subdividing for sharp, controlled topology.
• Edge-aware painting
  • With ridges unmasked, lightly Airbrush or use Spray with a subtle alpha to add edge wear and color breaks.
  • Combine with Mask by Cavity for nuanced grime vs highlight passes.

Practical tips:

• Scale matters: extremely small or huge meshes can skew results. If needed, Deformation > Unify (on a duplicate) to normalize scale for the operation.
• Refine the selection: Ctrl+click on the model to blur; Ctrl+Alt+click to sharpen. Use Grow/Shrink Mask to pad or tighten the selection band.
• Work per subtool: isolate the target piece in Solo mode to avoid unintended masking across hidden geometry.
• Mix with ZRemesher: after establishing edge Polygroups from the mask, enable KeepGroups and lower AdaptiveSize to encourage clean, animation-friendly loops around features.
• Snapshot safety: store a Morph Target before aggressive polishing so you can selectively restore areas with the Morph brush.

Troubleshooting:

• Noisy selection or speckling? Lightly use Polish by Features first, or step down one subdivision level and re-run Mask by Smoothness.
• Missing edges? Increase detail (subdivide or locally subdivide), then try again—edge detection thrives on sufficient resolution.
• Over-masking broad areas? Lower the Mask by Smoothness intensity and apply incrementally.

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