Modifying skin weights

You can modify the skin weights for any of the influencing joints to alter the irregular region. If you don’t get the desired results when you change the skin weights of one of the influencing joints, you can undo your changes and try another influencing joint.

In general, it’s best to modify the skin weights of the most influential joint first, then work with less influential joints if you don’t get the desired results. Modifying skin weights requires experimentation.

In the next steps, you’ll modify the skin weights for the left_arm_root joint.

To modify skin weights using the Paint Skin Weights Tool

1. Select left_arm_root in the Influences list.
2. Set the Mode to Paint, then set the Paint Operation to Add.
3. Set the Value to 0.1.
4. Drag to paint on the irregular region of the breast.

   As you stroke a region, a red circle icon indicates the area affected by the brush stroke. Each stroke adds 0.1 (10%) to the skin weight. The weight for a skin point has a maximum value of 1 (fully white).

   Tip

   To change the size of the red circle icon, change the Radius(U) value in the Paint Skin Weights Tool.

   Repeat the strokes several times until the irregular region becomes smoother. The jagged, asymmetrical wireframe at the breast becomes more symmetrical as the skin becomes smoother. The region whitens, which indicates increased influence from the left_arm_root joint. Note that increasing the influence of one joint lessens the influence of the other influencing joints.

5. To check the shape with full-color shading, click the Select Tool in the Maya Toolbox. (You might also prefer to cancel the selection of Jackie to eliminate the display of the highlighted wireframe.)
   
6. To continue modifying the skin weights, select Jackie and select Skin > Edit Smooth Skin > Paint Skin Weights Tool, or click in the Maya Toolbox.

   There are several additional tool settings you might find useful as you modify skin weights:

   • The Smooth paint operation smooths the weights of points by averaging the stroked points with the weights of the surrounding region. This is useful if you add to the weight values in some region but the points become unevenly weighted. Uneven weights are indicated by mottled gray skin.
   • The Weight Hammer button lets you select vertices in a region with undesirable deformation then click to quickly flatten the area. This tool checks the weight values of neighboring vertices and applies the same weight value to the selected vertices.
   • You can use the Scale operation with a Value less than 1 to scale down the point weights of a stroked region.
   • You can select any of the Profile icons to specify the region affected by strokes. The two leftmost icons are the most commonly used shapes.
7. After you eliminate the irregular region from the left breast, move the arm to different positions to see if the breast’s shape stays natural in various poses.

   It is common for a surface to look good in one pose but not in another. Strive to make the surface look good in the poses that you are likely to use during animation.

8. If you want more practice, pose the right arm as you posed the left arm and fix the corresponding irregular region in the right breast. This time, fix the region by modifying the weights for the upper_back joint rather than the right_arm_root. As mentioned previously, you can modify point weights of alternative joints to get a similar effect.