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Skin weighting and deformations
Lesson 2: Smooth skinning
Influence objects
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
- Select
left_arm_root in the Influence list.
- In the Paint Weights Menu section
of the window, set Value to 0.1 and turn on Add.
- Drag
the mouse pointer to paint the irregular region of the breast. Each stroke
adds 0.1 (10%) to the skin weight. The weight for a skin point has a
maximum value of 1 (fully white).
TipPainting skin weights using a tablet with
stylus allows you to take advantage of pressure sensitivity.
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.
- To
check the shape with full-color shading, click the Select
Tool. (You might also prefer to cancel the selection
of Jackie to eliminate the display of the highlighted wireframe.)
- To
continue modifying the skin weights with the Paint
Skin Weights Tool, select Jackie and once again select
Skin > Edit Smooth Skin > Paint Skin Weights Tool.
There are several additional tool settings you
might find useful as you modify skin weights:
- The Smooth 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.
- You
can use the Scale operation with a Value less
than 1 to scale down the point weights of a stroked region.
- As
you stroke a region, the red circle icon displays the radius of
the region affected by the stroke. The Radius(U)
value changes the radius.
- 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.
- 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.
- 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.