Create pre-skinning corrective shapes

Corrective shapes are blend shapes that you create in order to fix problems with the deformation on the base object. This is often a method used on a character's skin to fix specific deformation problems that you find when the character is animated. You can make the corrective shapes so that they're applied to the skin either before or after the skin deformer is evaluated. The shape deformation results and workflow are different for each method.

When you create a corrective shape on the skin that is evaluated before the skin deformer, it's like "fixing" the original character's mesh. This means that the shape on the skin looks correct in other poses as well.

To create a pre-skinning corrective shape

1. Go to a frame where the character's skin is deforming incorrectly, or move the character into a pose where you want to add a corrective shape.
2. Select the character's skin mesh.
3. Open the Shape Editor and choose Create > Blend Shape Deformer > .
4. In the Blend Shape Options, click the Advanced tab and select Pre-deformation from the Deformation Order list.
5. Click the Create button to create the blend shape deformer on the skin mesh.
6. In the Shape Editor, click the Add Target button to create a target shape for this blend shape deformer.
7. The target shape's name is automatically the same as the name of the skin mesh, but you can change it: double-click the name or right-click it and choose Rename, then enter a new name.
8. Make sure that the target shape's Weight value is set to 1 for 100% influence for the corrective shape's effect, and click its Edit button if it's not already red. You're ready to edit the skin mesh.
9. Use Sculpting tools to deform the skin so that it's correct, or select the object components you want and use Transform tools to deform the skin - see Edit target shapes for more information.
10. Click the Edit button again when you're finished the shape to exit edit mode.

When you drag the target shape's Weight slider, you see the effect of the corrective shape change influence on the skin mesh.

See Set weights for target shapes and Key the blend shape weights for information animating the corrective shape's weight.