Fixing Failed Automatic Bone Weight Solutions In Blender

Troubleshooting Failed Automatic Bone Weighting

When rigging character models in Blender using the automatic weight painting tools, poor results can often occur. Vertex groups may be assigned to the wrong bones, influences may overlap excessively, and deformations can appear broken or twisted. By examining the issues visually, artists can determine the needed corrections in weighting, vertex assignments, or armature constraints to achieve properly responsive deformations.

Signs of a failed automatic weighting solution include parts of the mesh deforming incorrectly or excessively when pose tests are conducted. Arms or legs may completely collapse, twist unnaturally, or retain their rigged shape against animation. This occurs because vertices along deformation boundaries have not been assigned suitable bone weight influences.

Inspecting Weight Paints for Errors

Enter weight paint mode to visually inspect the automatic weighting solution. Pay attention to boundaries between limb segments, joint areas, and regions prone to deformation issues like the shoulders or wrists. Incorrectly weighted vertices will display as bright red, floating blue, or dark purple splotches indicating a paint job in need of revision.

Zooming in on convoluted areas makes it easier to spot vertices assigned to the wrong bone groups. For example, vertices for the lower arm should transition smoothly from upper arm to elbow influence. Scattered upper arm group assignments along the wrist or hand is indicative of a poor automatic solution.

Analyzing Mesh Deformations

In pose mode, manipulate bones into bent or stretched positions to analyze how the mesh reacts. Twisted limbs, indentation artifacts, or collapsing joints imply overlapping weights or abnormal group assignments. The associated vertices are not properly locked to the correct bone chains.

For character meshes, analyze common poses like arm raises, leg lifts, torso bends, and neck turns. For quadruped models, check leg, spine, tail, and neck deformations both singly and in combination. Any deformation issues spotted can then be matched to errors in the automatic weighting.

Cleaning Up Bad Vertex Groups

Before corrective paint work can occur, improperly assigned vertex groups must be dissolved or removed. Entering edit mode and using vertex select tools makes it easier to target rogue group assignments.

Selecting Errant Vertices

In edit mode, vertex or face select tendrils, islands, and other oddities linked to unwanted bone groups. The vertex weights panel can display the bone group influence on selections, allowing unwanted groups to be identified.

For example, vertices showing influence for the lower leg that creep up the thigh indicate poor separation between leg and thigh groups. These can be selected using box select and dissolved from the thigh group.

Removing Vertex Groups

Using the vertex groups panel, remove the selected vertices from incorrectly assigned groups with the remove button. Dissolving all vertices finishes elimination. With the errant influence cleared, that body part can now receive proper group and weighting assignments.

In tricky cases with many overlapping groups, assign vertices to a new custom group using the add group button. Making careful selections, add all relevant vertices before removing them from all other groups with the remove from all button. This isolates them for correct weight painting.

Deleting Stray Bones

If extra bones were automatically generated, inspect their impact in pose mode before deletion. Select the extra bones and press X to bring up delete options. Choose dissolve from the menu to safely remove the bones and assign their vertex groups to the armature root.

Deleting bones with remaining vertex group assignments can cause crashes or severe deformation issues. Only remove automatically generated bones that serve no weighting purpose for the mesh.

Repainting Weights through Weight Paint Mode

With vertex groups cleaned up, enter weight paint mode to begin redistributing bone influences. Using the gradient brush, neighbors tool, and manual entry, unhealthy weight gradients can be smoothed into natural transitions.

Smoothing Hard Weight Edges

For areas exhibiting deformation stress like indentation or twisting, harsh weight boundaries are likely the cause. Using the gradient brush with a subtle curve, paint to soften the transitions between major bone group assignments.

Smooth weight changes prevent adjacent vertices from receiving too divergent of bone influence forces during animation. Hard edges can act like tears in cloth when posed, overriding seamless deformations.

Blending Overlapping Groups

Areas with heavy overlapping group assignments can be blended with the mix or subtract brush tools. Using mix, brush back and forth between the groups to normalize contributions in the problem area. Subtract can also be utilized to disentangle influences.

With practice reading weight gradients by color intensity, relationships between competing bone groups can be rebalanced. The goal is reducing overlaps while achieving symmetry across limbs and mesh segments.

Repairing Deformation Holes

For areas that collapse or indent when posed rather than deforming properly, weight assignments are lacking entirely. Use the draw or fill brush to add bone influence gradients back into the deformation voids.

Reference how surrounding vertices respond to posing, then use 25-50% weight to paint the problem area to match. This adds support from the corrected bone chains to fill gaps during animation.

Using Weight Normals to Balance Bone Influences

Once primary weights are laid down through painting, rely on weight tools like normals and smear to refine bone deformations. These save time balancing tedious vertex assignments for uniform influence across groups.

Allowing Normals to Relax Weighting

With the normals tool enabled, analysis of surrounding vertex group assignments occurs automatically as you paint. This introduces natural blending behavior between your strokes and the neighboring weights.

Enabling apply automatically continually refines weights as you work to minimize harsh transitions. Locking groups prevents oversoftening of key bone assignments. Use weight normals to automate the busywork of perfect gradients.

Smearing Consistent Weighting

The smear tool propagates defined vertex group assignments in a specific direction. For example, painting correct thigh weights then smearing towards the knee cleanly carries proportional assignments down the leg.

Smearing progressively from torso to fingers or shoulder to wrist allows expertly assigned core weights to channel down limbs. Match smear direction to the deformations for responsively chained bone influences.

Locking Vertices to Specific Bone Groups

For key deformation areas like wrist and ankle joints, directly editing vertex assignments prevents bones from competing. Locking the critical rotation points simplifies weighting dramatically.

Enabling Vertex Group Locking

In the viewport overlays section, enable the group option. Now selection will output the assigned vertex groups, allowing you to identify influence relationships for locking.

Confused vertices contributing to multiple limb segments can now be restricted solely to pivot controllers. Lock settings prevent unwanted bones from overriding critical handles during posing.

Assigning Locked Vertex Groups

Using selection tools, target joint hinge vertices and assign them to new empty groups. Shift selecting the same vertices, use remove from all groups before designating the new empty one as locked. Now scaling can increase the locked assignment.

With vertices locked to the precise bone handles, joints snap predictably during animation. Lock settings are vital for cleanly rotating wrists, ankles, elbows, and knees independent of neighboring distortions.

Troubleshooting Twisted Meshes and Deformations

Bent elbows or knees deforming with twisted topology indicates bones chains overpowering each other. To untangle erratic deformations, the weighted relationships between limb segments must be reassessed.

Analyzing Directional Influence

In pose mode, rotate troubling joints into fully flexed positions. Note bone rotations that trigger mesh twisting across limb segments. This reveals which controllers are battling for influence over shared vertex groups.

For example, a twisting knee joint may show upper leg bones overriding the lower leg weights during backwards leg flexion. The weighted influence directing knee handle bones must now be corrected.

Unwinding Vertices from Twisting Bones

In edit mode, select vertices following the twisted deformation paths using shortest path selection tools. Inspect their group assignments for influence from the problematic bones.

Remove the twisting bonesâ€TM influence over these vertices entirely. Volume select more vertices exhibiting twist distortion, removing them from the errant groups until mesh untwists convincingly during extreme poses.

Correcting Overlapping Bone Influences

Automatic weighting often leaves geometry dominated by too many strong bone influence overlaps. This manifests as knots and indentations when posing rather than smooth deformations. Targeted group removal is needed for tidy joint rotations.

Spotting Overlapping Group Artifacts

Selecting confusing vertex group assignments in edit mode reveals winding bone influence trails spreading across multiple limb segments. This causes deformations to fight each other.

Analyze the squashed rotation ranges of heavily overlapped joints. Remove groups with longest inherited trails to free up clean deformation ranges for the remaining controllers.

Streamlining Bone Influence Chains

Using remove, strip down competing influence chains to essential bones per joint. For example, upper arm vertices may only need shoulder and elbow groups for responsive flexing and extensions.

Dissolve all extra influence overlaps per region to give your core joint handles room to cleanly control deformations along uncompromised rotation arcs. Appropriately minimize blending across bones.

Setting Up Custom Vertex Groups

When cleaning up automatic weights fails or proves overly tedious, generating custom vertex groups bypasses the bad rigging foundation entirely. This strategy works best for meshes with clear anatomical divisions.

Subdividing Mesh Regions

In edit mode, make box selections dividing up the model along muscular contours and skeletal joints. Separate head, torso, pelvis, arms, legs, hands, feet, and digit segments for precise control.

Use edge loops, pole vectors, and mesh topology landmarks to intuitively partition major muscle groups and future deformation ranges. Assign each custom selection a descriptive vertex group name.

Weight Painting Custom Groups

Tabbing into weight paint mode, choose each named custom group to manually paint influence gradients across associated vertices using round or size falloff brushes.

Visualize how custom muscle sections should squash, stretch, and deform together during movement when distributing weights. Mesh segments can be further subdivided if needing distinct control.

Optimizing Armature Deform Settings

Beyond tuning weight gradients across vertices, adjusting default armature properties improves posing and deformation responsiveness. Settings like preserve volume and bone envelopes reduce distortion artifacts.

Allowing Mesh Volume Compensation

Under object data properties, enable preserve volume in the armature settings. This tells the engine to compensate for changes in surface density from scaling during posing so form is retained.

Volume preservation prevents unrealistic bulging, pinching, and shrinkage when flexing muscle groups. This helps correct mesh collapsing in essential deformation zones that may lack fine tuning.

Configuring Bone Envelopes and Radii

Adjust bone radius values and envelope volumes in armature edit mode until mesh binding visually updates as desired during movement. Expand envelopes to reincorporate missed vertices or shrink to cull error groups.

Tune envelope boundaries until vertices deform naturally without Birdtracking or detaching from moving bones completely. Use X-Ray mode to ensure no gaps exist between bones and geometry.

Automating Tedious Weight Paint Tasks with Python

Once skilled at manual weight painting, artist workflows can be augmented with scripting to save repetitive brushwork time. Iteratively corrective tools like transfers and projections work better automated through code.

Speeding Up Group Transfers

After mastering deformations across one mesh side, use vertex group transfer scripts to clone completed weights to unpainted areas. Customize mix values to retain some uniqueness between mirrored assignments.

For organics, small variations improve realism but for symmetric mechanical items like robots, raw transfers may suffice. Automated propagation removes tedious duplication effort.

Quickening Projections

Projection painting dynamically updates weights based on mesh proximity changes over time, needing manual invocation each frame. Script this invocation so projections run automatically as simulations deform.

Projecting from stable rigged templates eliminates laborious paint corrections trying to match bokeh and flex sim artifacts by code, freeing artists for higher value tasks.

Achieving Realistic and Responsive Deformations

Bone weighting mastery combines both technical knowledge and artistic finesse for lively, convincing model animations. Learning to diagnose and strategically improve failed automatic solutions takes practice across varied meshes and creatures.

With time manipulating vertex groups, brushes, and armature properties, artists can create highly customized deformation networks. Match rigging controls to natural movement flow and ranges of motion unique to any character.