Week 8: Skinning

Been offline for a while since skinning week was really intense and not much time for much else. Unlike other weeks, there aren't that many examples to show as the concept is rather simple but the work is very tedious and difficult to do get exacting results without lots of work.

The term 'skinning' is not unlike the hunting term (where animal's skin is removed) but in this case we are putting on skin, not taking off. Just like a real person, characters have a skeleton with joints that move and the skin follows along. It's the same in 3d but..and its a big but..it the skin moving with the bones doesn't just happen automatically. One has to go in assign each vertex in the outer skin to a joint inside and then decide how much influence that joint has over that point. If its 100 percent, then moving that joint will make that point follow it 100%. if 50% assignment, then the movement of that skin vertex will move some average of that joint and of the position of whatever other bones of which that vertex is a member. When done correctly, arms bend and stretch correctly, wrists turn and everything behaves as it should. This kind of work is only noticible to most people when something doesn't look right. So it's kind of an invisible art. I think skinning and rigging artists are the unsung heros of 3d character animation.

In the image above, the white areas are showing 100 percent assingment to the elbow and black areas have no assignment, i.e. wont deform when the joint is bent. Grey areas have multiple joints assinged to the those vertices. The cool part is if you have a pen and tablet, like a wacom, you can paint these assignments with the pen using white and black colors. So literally you are painting the influence a selected joint has on the skin. It makes the process faster and more bearable then if had to just use a mouse or assign the numbers by data input. The red circle in the image is the brush shape i was painting with.

The finishing touches related to skinning include the use of deformers. Skinning itself is a deformation proces but with other deformers on top you can make a muscle flex when the arm is bent or correct and area around a joint that isn't deforming/bending propertly. Once assinged, just bending the arm will make the bicpes flex, etc. It's really cool.

In the clip above, I'm showing the calethenics test that characters are put through when doing skinning. It's the best way to see how things are bending and what areas need more tweaking. Also you can see me grab come small points called clusters which are a type of deformer I assigned to the areas in and around the biceps/elblow are to correct the bend and make the bicep flex when the arm is bent.

Not much else to say or show about skinning, as i said it's easy in concept but just lots and lots of testing and tweaking. I liked it since i got to feel some sense of painting again, but I don't think I would like doing it everyday for months on end.

Last (and coolest) week coming up: Dyamics :P