Back at time=0, turn on "Envelopes."
Note the proxy bone lines that appear for each hidden biped bone.
Select one of these proxy bone lines to see the envelopes, which are shaped as two capsules: a bright red inside and dark red one outside. Hit [F4] to view the vertices effected by the selected bone. The proxy bone lines can be moved, rotated, and scaled by selecting and moving the pink end-points. the capsules can be scaled by selecting and moving any of the four points around the capsule ends.
These proxy lines and envelope capsules represent the bone SKINNING. While the proxy lines are initially set based on the positioning of the real biped bone and the capsules on their sizing, adjusting them will not affect the original bones: just what part of the mesh is affected by each bone.
HOW DO THE ENVELOPES WORK?
Any mesh inside of the red capsule is not supposed to be shared with any other bone (good for the middle of limbs). Mesh that sits only in the dark red capsule is shared, with is good for joints such as elbows and knees.
After adjusting each envelope, test the result by scrubbing the timeslider, but set time back to 0 for further adjustment to envelopes in the keyframed bind pose.
Vertex Colors: red means the mesh is fully bound to the selected bone. Blue means that part of the mesh has almost no affect from that bone. Yellow and orange are in the middle.
NOTE: initially, neighboring envelopes will generally be too big and will interfere with each other. The whole body will need to have its envelopes reduced in quick draft before refining each envelope to perfection in further passes.
A) ELBOWS AND KNEES:
Move the pink end-points of the arm and leg proxy-lines away from the elbows and knees so only the dark capsules surround the mesh joints (imagine two ovals intersecting at the knee). This should result in a nice crease in these joints when testing the animation.
B) SPINE LINKS:
Adjust the 3 spine links. Typically this means scaling down so that the spine envelopes do not interfere with the arms, head, pelvis, and each other. Depending on the shape of the torso, sometimes it is advantageous to change the orientation of the spine bones for horizontal capsules rather than vertical ones.
Adjust the Pelvis envelope, so that the dark red capsule overlaps with the upper leg capsules at the hip joints. The COM's perpendicular line can be used to maintain butt and front.
D) HANDS AND FEET:
Adjust the envelopes for the hands, fingers, feet, and toes. Typically this means scaling the envelopes down so that each part does not interfere with its neighbors. End nub capsules can be scaled small enough to affect no vertices at all.
Adjust the head bone proxy and envelopes so it does not interfere with the shoulders, and vice versa, and so all evryices in the entire face are fully connected ot the head bone (appear fully red wehen the head bone is selected).
Adjust other bone envelopes: tail, wings, etc. to not interfere with other body parts.
NOTE ON VERTEX WEIGHTING: It is possible to assign specific vertices to specific bones, and decide the weighting for precisely how much that bone effects that vertex. This can be useful to assign all the head and face vertices 100% to the head bone. Note that many game engines do not support vertex weighting.