Skin weighting and deformations

In the next steps, you’ll learn how joints and skin weights influence deformations at Jackie’s chest. In a subsequent section, you’ll improve uneven deformations.

To see how skin weights affect a skin’s deformation

1. Pose the left arm similar to the following figure. The left breast becomes irregularly shaped.
   
2. Select Jackie.
3. Select Skin > Edit Smooth Skin > Paint Skin Weights Tool > .
4. In the Influences list of the Tool Settings window, select any joint, for instance, pelvis.

   The grayscale color of Jackie’s skin indicates how much influence the selected joint has on the skin deformation. In general, a white region of skin is influenced nearly entirely by the selected joint. A gray region is influenced significantly by one or two additional joints, and a black region indicates skin not influenced by the selected joint at all.

   Tip

   If you prefer, you can turn on Use Color Ramp in the Gradient section of the Paint Skin Weights Tool to view the influence feedback in color. This can make it easier to see small weights.

   Each point on Jackie’s surface is influenced by three joints, as specified by the Max Influence setting in a prior step. However, one or two of the three joints might have so little influence as to be insignificant.

   In this case, the left breast becoming irregularly shaped as you pose the arm indicates that one or more of the joints is exerting too much or too little influence on the surface. In the next steps, you will determine which joints are influencing the irregular region.

5. Do the following to select the vertices in the problem area:
   • In the Paint Skin Weights Tool, turn on Paint Select mode (below the Influences list).
   • Right-click Jackie’s skin and select Vertex from the marking menu.
   • Paint to select the vertices around Jackie’s shoulder.
6. In the Paint Skin Weights Tool, click the Show Influences button.

   All joints that influence the selected vertices are selected in the Influences list.

   Tip

   If you don’t immediately see the selected influences in the list, scroll to find which influences are selected.

   Depending on which vertices you selected, the Influences list shows you that the main joints influencing this region are from the mid and upper back, and the left arm.

7. Now that you have narrowed down which joints are influencing the shoulder, select each entry in the Influences list individually to view the shades of gray on Jackie’s skin.

   The left_arm_root is the main influence. The upper_back, mid_back, and left_top_rib also have influence, though not exactly in the same region.

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