Weighting the Character's Lower Half

In this portion of the tutorial you learn to improve the skinning by adjusting the Weight setting for vertices with respect to rig bones, thus determining how the rig animation affects the character mesh. You start with the lower half of the character, beginning with the feet.

Set up the lesson:

Continue from the previous section or click File menu > Open, navigate to the \character_animation\skinning\ folder and open the file configuring_skin.max.
Note: If a dialog asks whether you want to use the scene's Gamma And LUT settings, accept the scene Gamma settings, and click OK. If a dialog asks whether to use the scene's units, accept the scene units, and click OK.

This scene contains the Emma character skinned and animated, with the correct links already in place and the rig hidden.

Start skinning the character:

Note: Much of the information in this procedure and the following one provides background information on how Skin works. We recommend you read over it now, but don’t worry if it’s not fully comprehensible. Continue working through the tutorial, following the steps and reading the explanations, and after you’ve gained some hands-on experience with adjusting Skin, return here and read these explanatory sections again. They’ll probably make a lot more sense the second time around.

Scrub the time slider or play the animation and check for problem areas. For example, around frame 70 the knees become narrower, and thus look unnatural. Even more blatant is the distortion of the shoulder around frame 210.
Important: Loss of volume, such as the narrowing of the knees when they bend, is the main thing to correct for when adjusting character skinning. A potential second issue is the interpenetration of the mesh around bent body joints, but that tends to be less noticeable in the final animation, and can be accounted for to an extent by attributing it to folds in the character’s clothing. This tutorial focuses on correcting for volume issues.
Return to frame 0.
Make sure (Select Object) is active . Select the Emma object and go to the Modify panel. On the Parameters rollout, click Edit Envelopes.
The character mesh turns gray except for a color gradient around the current bone object. The gradient shows the weighting of the skin vertices assigned to that bone.

The term “weighting” will be explained shortly.

Tip: The Skin modifier has quite a few parameters spread out among several rollouts. In some cases you might want to see more settings than can fit comfortably in a single column. To expand the command panel, position the mouse cursor over the left edge so it becomes a horizontal, two-headed arrow, and drag leftward until you see two columns.
Drag the left edge of the command panel to the left to expand it to multiple columns.
Try clicking some of the other entries in the Bones list to see the weighting of vertices in other parts of the skin mesh. Alternatively, click the bone representations in the viewport; each is displayed as a straight line with a (non-mesh) vertex at either end. As you do so, the highlighting in the list on the Parameters rollout switches to that bone.
Bones appear as straight lines with vertices at the ends.

A bit of background info on how the Skin modifier works is in order here. When you add bones to Skin, the modifier looks at the mesh to which it’s applied and automatically assigns each vertex to one or more bones based on proximity. It also calculates a Weight value for each bone assigned to a vertex to specify the degree to which moving the bone affects the vertex; again, this is based on proximity. If a vertex is close to one bone but relatively distant from any others, it’s assigned to that bone with a weight value of 1.0, which means 100%. In other words, the vertex responds to movement of that bone only, and moves in exactly the same direction and distance as the bone.

If, however, a vertex is, say, equidistant from two bones but far from any others, Skin assigns both bones to the vertex and gives each a Weight value of 0.5, or 50%, for that vertex. In such a case, the motion of both bones contributes equally to that of the vertex. If only one of the bones moves, the vertex moves half that distance. This is how the Skin modifier accommodates for the motion of a character mesh around bending joints such as knees and shoulders.

The Weight values for a highlighted bone appear by default on the mesh as a gradient, with red representing higher weights, decreasing to orange, yellow, green, and then blue for the lowest values. Vertices use the same color scheme, and since you’ll be adjusting weights at the vertex level, it’s usually best to have the viewport set to Realistic + Edged Faces display mode (toggle with F4) or Wireframe mode (toggle with F3). (If you use a Direct3D or OpenGL display driver, Smooth + Highlights is the equivalent of Realistic.)

Incidentally, the Skin modifier determines which vertices are affected by a bone or bones by creating an “envelope” around each bone, which is a capsule-shaped 3D volume that you can edit interactively to adjust the vertex weighting at a high level. However, you have better control by adjusting Weight values for individual vertices and groups of vertices. This is the more common practice in professional environments such as game-development studios, so it’s the one this tutorial focuses on. This method is more painstaking, but can produce optimal results reasonably quickly.

Make no mistake, however: Skinning a character is a detail-oriented task, and requires lots of experimentation and trial-and-error, so it benefits from a liberal supply of patience. This aim of this tutorial is to demonstrate the overall process, but it’s impractical to describe every step in detail in such a context. In other words, we can’t show you exactly what to do every step of the way, but instead provide guidance and examples; the rest is up to you.
Save your work under a different filename, such as MyEmma3.max.
We won’t keep reminding you, but it’s important to remember when going through a complex method such as skinning a character to save your work incrementally as you go so you can easily return to a previous version if things start to go wrong.

Examine some Skin modifier options:

You edit a vertex’s weight by changing its Weight value with respect to a particular bone. In order to do that, the vertex must be assigned to two or more bones, because Weight is a relative value. For a given vertex, if its Weight value with respect to bone A is, for example, 0.6, and its Weight value with respect to bone B is 0.4, then bone A’s motion has half again as much influence over the vertex’s motion than does that of bone B. The total of Weight values for each vertex must always equal 1.0. So, when skinning a character using this method, you need to know which bone or bones a vertex is assigned to and the Weight values for all vertex-bone assignments.

Note: Best practice when skinning a character, which this tutorial follows, is to focus on one body part at a time. When you're done with that part, mirror the changes to the other side, as appropriate. To be more specific, you select a bone, make sure most of the surrounding vertices are set to a Weight value of 1.0, and then adjust the weights in the bending areas. You can think of this as “blocking out” the weighting, much as you block out an animation by working on isolated segments of the character’s movement before integrating the overall motion.

For example, in this tutorial you’ll start with the left leg, working upward from the foot bone, and then mirror (copy and flip) the vertices’ settings to their counterparts on the right leg. You can always go back later and tweak the weights anywhere, but you work most efficiently by concentrating on a specific area at any given time.

Even though you won’t be editing envelopes directly in this tutorial, it might help you better understand how Skin works by taking a quick look at this feature of the modifier. By default the envelopes are set not to display in this scene, but you can enable them by going to the Display rollout and turning off Show No Envelopes.
With the forearm bone selected and Show No Envelopes off, the capsule-shaped inner and outer envelopes appear in the viewport.

As a very brief explanation, each envelope comprises two concentric capsule-shaped volumes; vertices within the inner volume are fully affected by that bone, and then the weighting falls off increasingly for vertices that lie outside the inner volume and inside the outer volume. Select some of the different bones to see their envelopes, and then turn Show No Envelopes back on again.

Using envelopes is a fairly crude, high-level method of setting vertex weights in Skin, and is suitable mainly for saving time when skinning fairly simple bone-and-mesh setups.
Turn Show No Envelopes back on, as you won’t be using envelopes in this tutorial.
While you have the Display rollout open, take a look at the other options here.

Show Colored Faces is on; you’ve already seen its effects.
If you turn on Color All Weights, you can see the vertex weighting throughout the character mesh, not just for the current bone.
With Color All Weights on, weighting is visible for the entire mesh, not just the selected bone.

That’s not what we want for this tutorial, so turn it back off.
If you turn off Draw On Top Envelopes, you can no longer see the bone representations superimposed on the mesh, so keep that one on.
Disabling envelope display makes it impossible to select a bone in the viewport.
Try the other options if you like, but when you’re done be sure to restore them to their previous settings, as shown here:

Begin adjusting vertex weights:

Back on the Parameters rollout, turn on Select Vertices.
This setting is off by default, but it needs to be on for adjusting vertex weights, so always turn it on before starting a skinning session using the method described in this tutorial.

The “stretching” animation begins with the feet and moves up the body, so you’ll follow the same progression in adjusting the skinning.
Zoom in on the calves and feet, and make sure the display is set to Realistic + Edged Faces, as shown in the following illustration.
Scrub back and forth through the first 50 frames or so of the animation. Notice how the bending of the feet also affects the bottom portion of the calves. This is not realistic; it happens because the default envelope assigned by Skin to this bone is a bit too large.
Select each of the foot bones in turn: EmmaRigLCalf, EmmaRigLAnkle, and EmmaRigLToe.
From left to right: calf, ankle, and toe bone selected.

End with EmmaRigLAnkle selected. The shading (orange, yellow, and blue) indicates that most of the vertices’ weights for this bone are less than 0.5, which is undesirable.
On the main toolbar, from the Selection Region flyout, choose the Lasso Selection Region tool.

This is the best tool for region-selecting a contiguous group of vertices with an arbitrary outline.
Drag a region around the foot and ankle vertices, as shown:

Because the Backface Cull Vertices checkbox is off, this also selects most of the vertices facing away from you. Depending on the view angle and where you drag the region, a few vertices might not be selected. To make sure all foot and ankle vertices are selected, orbit around the model to double-check. Add any vertices you missed to the selection, and remove any vertices that shouldn’t be selected.

To undo the orbit, press Shift+Z.

Tip: To add vertices to a selection, Ctrl+click them, and to remove vertices from a selection, Alt+click them.
On the Parameters rollout, in the Weight Properties group, set Abs. Effect to 1.0.
Absolute Effect is the absolute weight setting.

The entire foot turns red, as a visual result of the weight setting change. This way you know that no other bones can influence these vertices.

You can confirm that the toe animation no longer affects the foot mesh by scrubbing the animation. You’ll fix that next.
Select the toe bone (EmmaRigLToe).
The foot is gray, indicating no weighting for this bone, but some blue coloring is evident in the shin, indicating influence that the toe should not have over this area.
Drag a region around the blue vertices (it doesn’t hurt to select too large an area), and then set Abs. Effect to 0.0.
This removes any remaining leg vertices from the influence of the toe bone.

Next you’re restore the vertices at the front of the foot to the influence of the toe bone.
Drag a region around the front of the foot, just above the third lace (raised portion at the top of the shoe). Again, orbit around the model to make sure the selection is correct. To undo the orbit after the selection is correct, press Shift+Z.

Tip: A good way to check quickly whether your selection is correct is to use (Zoom Extents Selected). For example, if you inadvertently selected vertices on the other side of the character, the resulting view will be wider than expected.
Set Abs. Effect to 1.0.
The selected vertices and surrounding mesh turn red. Now, when you scrub the animation, the break between the weighted and unweighted vertices for the toe bone is readily apparent, as compared to the right foot. At the greatest amount of bend, around frame 10, the fourth lace (unweighted) sits directly below the third lace. If you select the ankle bone, you can see that there’s no transition between the weighting at the front and the rear of the foot.

The way to resolve this is to create a transition mid-foot by weighting those vertices between the two bones.
Return to frame 0 and then select the vertices for the two uppermost laces.
Drag upward slowly on the Abs. Effect spinner so you can see the color change as the vertex weighting increases. Stop when you see a yellow-orange color, around 0.4.

When you scrub now, the transition looks better. However, the uppermost lace is too low.
Select the vertices of the uppermost lace, select the ankle bone, EmmaRigLAnkle, and drag the Abs. Effect spinner gradually upward.
As you do, you see the lace move upward due to the increasing influence from the ankle bone. Stop around 0.6 or 0.7.

Tip: For a useful guide while adjusting clothing vertices, keep in mind the material of the clothing. For example, the sneakers might be made of canvas, which is a fairly stiff fabric, so creasing that might not occur with a softer fabric might be permissible for canvas. Also, with medium-resolution models like this one, there might not be enough vertices for a fully natural look, so a certain amount of compromise is necessary.
Continue adjusting the lace vertices around the bend until you get a reasonable-looking effect.

Note: Adjusting the laces is a good example of the back-and-forth type of adjustments required for good skinning. First you make the gross settings for the front and rear portions of the foot, then you go in and select one lace at a time and adjust it so it looks good with the rest of the laces in the bend.
Next, looking at the bottom of the foot, you might notice a fairly wide gap between the set of vertices at the bend and those immediately behind them. Again, select the offending vertices and raise the Abs. Effect spinner value gradually until the shoe looks more realistic.

Tip: In general, when adjusting vertex weights for a skinned character, try to keep polygon sizes consistent; this allows for minimal distortion when the character is animated.
Advance to animation to frame 20, where the foot is bent the furthest in the opposite direction.
There’s a fairly sharp bend at the bottom of the foot, but there’s not much you can do about it because of the relatively low resolution of the character mesh. Even if the budget allowed for more polygons in the mesh, they would probably go into the face, which has higher priority, so this type of distortion is usually tolerated in commercial applications such as games.

Weight the rest of the leg:

Zoom out and select the ankle bone, EmmaRigLAnkle. Check the animation that it affects, approximately from frame 30 to 50.
It looks all right, but the ankle influence goes fairly far up the calf, which is incorrect.
Select all of the affected calf vertices. It doesn’t matter if you go too high, but be sure not to select any of the ankle vertices.
Wireframe display makes it easier to see the selected vertices, which are outlined in white.
Select the calf bone, EmmaRigLCalf, and set Abs. Effect to 1.0.
This removes the calf vertices from the ankle bone’s influence.
Select the loop of vertices at the top of the ankle and set them to 1.0 for the calf bone as well.
Tip: This is a good place to take advantage of the Skin modifier’s loop-selection tool. Select two adjacent vertices on the loop of edges around the ankle and then, near the top of the Parameters rollout, click the Loop button. This automatically selects all the vertices in the same edge loop as the two vertices you selected.

Lower than this is where the ankle bends, so you need to weight the vertices between the ankle and calf bones.
Select the next loop down and set the calf weight to 0.5.

This loop is now weighted half for the calf bone and half for the ankle bone.
Next, zoom out, if necessary, so you can see both legs.

Some vertices on the right leg are influenced by the left calf bone, which you can easily correct for.
Drag a region around the affected vertices in the right leg. Toggle wireframe display mode and orbit around the model to make sure you get all of them.
Set Abs. Effect for the selected vertices to 0.0.
Similarly, the calf has a bit too much influence over the thigh vertices of the left leg, which is part of the cause of the loss of volume in the knee when it bends. You’ll deal with this in a bit, but first take a look at the thigh.
Select the thigh bone: EmmaRigLThigh.
Again, the default volume of influence is too large.
Go to frame 0 and select all the vertices on the right side of the mesh (your left side) and set their weights to 0.0.

Great precision isn’t necessary here; the main thing is to remove the right-side vertices from the influence of the left-side bone.

Start using the Weight Tool:

In this section you’ll continue to block out the leg weighting, using the convenient, powerful Weight Tool dialog.

Given a selection of vertices with the same bone and weight assignments, Weight Tool lists all bones that affect the vertices along with the corresponding Weight values. It also lets you edit the Weight value for the current vertex selection and bone assignment, setting either an absolute Weight value or adjusting the weights of the vertices relative to their current values. In addition, Weight Tool provides controls for copying and pasting Weight values and controls such as Ring and Loop for modifying the vertex selection.

Note: If you select multiple vertices with different Weight values and bone assignments, the Weight Tool dialog shows the settings for the vertex with the lowest sub-object ID. To see settings for more than one vertex at a time, use the spreadsheet-like Weight Table.

Near the bottom of the Parameters rollout, click (Weight Tool).
The Weight Tool dialog opens. Drag it to a convenient, out-of-the-way location. You can keep it open as you work.
Select different vertices while keeping on eye on the list at the bottom of the Weight Tool dialog.
The list shows the selected vertex’s bone assignments and the Weight value for each assignment. Note that the Weight values always add up to 1.0. If, for example, you change the Weight value for a particular bone for a vertex that’s influenced by three different bones, 3ds Max changes the values for the other two bones in the opposite direction, in proportion to their current values.

Note also that the Set Weight value doesn’t change; this is a write-only field.
Select all the vertices in the lower half of the knee area, down to the bottom of the Capri pants.
Make sure the calf bone is highlighted in the Weight Tool list, and then click the 1 button on the Weight Tool dialog.

This sets the Weight value for all selected vertices to 1.0 with respect to the calf bone. Note that the weights for the other two bones in the list are now 0. You can get rid of 0 weights in the entire mesh by clicking Advanced Parameters rollout Remove Zero Weights, but thats not necessary at the moment.
Select the thigh vertices above the knee, select the thigh bone, and click the 1 button on the Weight Tools dialog.
Just to clean things up, select the calf bone in the right leg and any vertices in the left leg that it influences and set their weights to 0. Do the same thing for the right thigh bone.
Note: After you select the right-leg calf or thigh bone and then region-select the affected left-leg vertices, it’s possible that the bone doesn’t show up in the Weight Tools dialog list because the selected vertex with the lowest ID isn’t influenced by that bone, but that’s okay. Just go ahead and click the 0 button on the dialog; 3ds Max still recognizes that you’re setting the weights for the selected bone.

This goes toward the general philosophy that you work more efficiently by keeping things as clean as possible as you go, rather than going back and trying to optimize them later. It’s analogous to the modeling practices of paying attention to edge flow and making as many polygons as possible quadrilateral, avoiding triangles or n-gons.

Fix the knee:

Go to frame 40 and adjust the view so you can see both knees.

This is a good before-and-after view. The right knee is “before,” showing marked volume distortion, while the left knee, after blocking out the thigh and calf weights, looks more realistic.

However, if you look closely at the back of the left knee when the leg is bent, it’s apparent that a good deal of fine-tuning remains to be done. This requires a lot of tweaking, experimentation, and examining the results, and, again, it’s not practical to give every detail of the process here. We will, however, give you an example to start you off.
Start by selecting the calf bone, if necessary, and then select the uppermost loops of vertices around the top of the knee. These aren’t technically loops (they merge and split off), so select them manually, combining region selection and clicking, rather than with the Loop tool described preceding.
Go to frame 40, where the leg is bent the most at the knee, and reduce the weighting gradually until the vertices are better positioned.
Tip: One good way to do this is to repeatedly click the – button all the way to the right of the Set Weight button. Each click subtracts 0.05 from the current Weight value of each selected vertex. Likewise, each click of the + button next to it adds 0.05 to the weights.

If you’d like to take a look at the completed, fully skinned model, open the included file configuring_skin_finished.max In that file you can examine the weighting for all vertices that we came up with through extended trial and error.

In general, what we ended up doing was weighting the vertices in the lower half of the knee mainly to the calf, and, starting halfway up the knee, giving gradually more weight to the thigh. Some manual tweaking was required to accommodate for the “wrinkle” vertices at the back of the knee.
As you’re going through and adjusting vertex weights, you’ll probably encounter bones for which the selected vertex has a 0 weight. To keep things simple, if you’re not planning to influence that vertex with the bone, make a practice of clicking the Remove Zero Weights button on the Advanced Parameters rollout. This affects the entire mesh, and helps keep things as simple as possible.

Weight the pelvis:

After you finish skinning the left leg, it’s time to move up to the pelvis.

Select the pelvis bone: EmmaRigPelvis.

Following the practice of blocking out the weighting, the fact that no red is visible is not a good sign.
For the reason why, select the thigh bone and note that it has an inordinate amount of influence over the pelvic vertices.
With the thigh bone still selected, select all vertices between the bottom of the pelvis (including the top of the side pouch on the pants) to the top of the belt, inclusive.
Select the pelvis bone and set the Weight value to 1.0.
Scrub the animation and stop around frame 67.

The schism between the weighting of the pelvis and thigh is glaringly obvious. Fortunately, fixing this is relatively easy.
Go to frame 0 and select the vertices at the crease between the leg and pelvis, at the front of the body only. Make sure not to select any vertices on the rear end.
Go back to frame 67 or so and then reduce the weighting so the vertices move up and out of the deep crevasse they were in, giving a more natural look to the bend.

Complete the leg and mirror the weights:

In this section you’ll correct the weighting on the vertices in the character’s rear end, and then quickly fix the weighting on the right side by mirroring the vertex weights from the left side.

The first thing to fix is some unwanted influence of the first spine bone on some pelvic vertices.

Select the EmmaRigSpine1 bone and note that several vertices in the front of the pelvis area, on the left side, are highlighted.
The bone also influences vertices on the right side, but because you’ll mirror all the vertex weights from the left side to the right, that’s not a concern.
Select the highlighted vertices on the left side (don’t worry about selecting too many) and then click the 0 button on the Weight Tool dialog.
Next, select the nine vertices in the lower crease, near the bottom of the rear end, as shown in the following illustration.
Select the nine vertices on the character’s lower backside.

Tip: You can select the vertices by clicking each in turn, holding down Ctrl after the first one. Another, slightly easier way, is to turn on Backface Cull Vertices in the Select group on the Parameters rollout, and then region-select the vertices. Make sure the Weight Tool dialog shows “9 Vertices Selected” and be sure to turn off Backface Cull Vertices after making the selection.

Currently these vertices are weighted only for the pelvis bone, so you need to add weighting for the thigh bone.
Select the thigh bone, set the vertex weights to 0.5, and adjust from there. For example, the lowest three vertices on this crease stick out too much, so you need to increase the thigh-bone weighting for them compared to the other six vertices.
Continue working on the vertices in the rear end, adjusting them so you get a realistic, rounded effect, like this:

As before, when in doubt, refer to the finished scene, configuring_skin_finished.max, for specific guidance.
Also adjust the vertices in front, at the crease between the thigh and pelvis. And while you’re at it, set weights to 0 for any torso vertices influenced by the thigh bone.
When you’ve finished weighting the pelvis vertices, go to the Mirror Parameters rollout and turn on Mirror Mode.
The bones and vertices now use color coding: blue for the left side and green for the right. Centered items, which cannot be mirrored, are colored red.

A few notes about the Mirror Mode settings:
- Mirror Plane The axis normal of the plane about which the vertex weights are mirrored. The default setting, which you’ll use for this tutorial, is X, which means the YZ plane. The plane appears as an orange wireframe in the viewport.
- Mirror Offset The distance along the X axis to move the mirror plane. The default value, 0, centers the plane to the character, so for this tutorial it’s the desired setting.
- Mirror Thresh(old) The amount of leeway for the detection of symmetry. If this is too high, mirrored weights might go to the wrong vertices, but if it’s too low, the Skin modifier won’t be able to detect symmetrical bones and vertices. You’ll experiment with this setting in the next step.
Right-click the Mirror Thresh. spinner to set it to 0, so that all the bones turn red, and then increase it until all the leg bones and arm bones turn blue and green.
The default value is 0’0.5”, but in our scene we were able to reduce this to 0’0.19”, which potentially allows for greater accuracy in mirroring weights. Your results might vary slightly.

To do the actual mirroring, you use the five buttons under the Mirror Mode button. From left to right, they mirror selected vertices only, all bones from either side to the other, and all vertices from either side to the other. For this tutorial, you’ll use Paste Blue To Green Verts, the button outlined in red in the following illustration:
On the Mirror Parameters rollout, click (Paste Blue To Green Verts).
All of the weighting you’ve done for each vertex on the left side of the character has now been copied to the vertices’ counterparts on the right side, instantly correcting the skinning throughout that side. The left-side vertices, previously blue, are now yellow to indicate that they’ve been mirrored:
Exit Mirror Mode by clicking the Mirror Mode button, and then scrub the animation through the first 100 or so frames.
The animation looks mostly good on both sides of the character’s lower half. However, there’s a slight problem around frame 80, when the leg bends back, where the crease between the leg and buttock is a bit too deep.
Select the crease vertices and increase their weights gradually with respect to the thigh bone until the folding looks better.
Tip: A tool that can potentially help in a situation like this is Blend, which evens out, or averages, the weighting of selected vertices. First save your work as a backup, then select the vertices in and around the area of the crease and then, at a frame where the crease is in effect, click Blend on the Weight Tool dialog a few times. If it looks better, great. If not, reload the saved file and weight the vertices manually.

When you’re satisfied with the results, mirror the vertices to the other side.

Another important consideration is the center line of vertices around the pelvis, which are currently weighted 100% for the pelvis. In reality, these areas would be pulled around by the movement of the legs, so they need to be weighted accordingly.
Select the three center vertices at the bottom-front of the pelvis, select the right thigh bone, and click the 1 button on the Weight Tool dialog. Then select the left thigh bone and click the .5 button. Finally select the pelvis and gradually increase its weight for the vertices, checking the animation as you go, until it looks right.
That way you give equal weight to both thigh bones, maintaining that balance as you then bring the pelvis into the equation.
Similarly, weight the vertices on the character’s left side of those center vertices slightly toward the left thigh bone, and the ones next to those a little bit further toward the left bone. When everything looks good, mirror the vertices to the right side.

Save your work:

Click (the Application button), choose Save As, and save the scene as MyEmma4.max.

Weighting the Character's Upper Half

Weighting the Character's Lower Half

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