Weight painting
Paint bone influence by hand where Auto Weight and the weight area do not quite get it right.
Auto Weight and a bone's weight area (see Binding and weights) get most joints looking right in one pass. Weight painting is for the rest: a shoulder that pinches, a fold that should not move yet, an influence that needs to fade out sooner than the automatic falloff gives you.
Turning on the brush
Select the Bone Bind Tool and turn on Weight Paint in its options bar. With a bone selected, dragging across the canvas raises or lowers that bone's influence on the points under the brush. Clicking within a few pixels of a bone re-selects it instead of painting, so you can switch which bone you are weighting without leaving the tool.
Painting on and off
The Weight / Unweight pill decides whether the brush raises or lowers influence; holding Alt while you paint does the same as switching to Unweight, so you can erase without changing the pill back and forth. Every point the brush touches is renormalised afterwards, so a point's weights across all its bones always add up correctly.
Strength, size and falloff
| Control | Default | Range | What it does |
|---|---|---|---|
| Radius | 40 px | 5 to 300 px | How far the brush reaches on screen |
| Strength | 50% | 1 to 100% | How much influence one stroke adds or removes |
| Falloff | Linear | Linear / Smooth / Hard | How the effect fades from the brush centre to its edge |
Smooth falloff gives the gentlest blend between full and no effect, Hard applies the full strength everywhere inside the radius, and Linear sits between the two. On a tablet, strength also scales with pen pressure, so a light touch paints a lighter change even at full Strength; a mouse always paints at full pressure.
Checking your work
While Weight Paint is on, every point on an editable Shape or Mesh layer shows as a small dot coloured on a heat scale from blue at zero weight to red at full weight for the selected bone, so you can see exactly what you are about to change before you paint. The brush itself is drawn as a ring at your current radius, with a smaller core showing how strongly the centre is painting; the ring turns red while Alt is held to erase.
Pose the rig afterwards and watch the seam you were fixing. A weight map only has to be as good as the poses it needs to support: there is no reason to perfect a joint no animation ever bends hard.