Kinematics: Human Figure Character Animation

Kinematics, in computer graphics language, is motion created by the force of another material body in motion—usually something that's attached, as a hand is to an arm. If the arm is moved, then the hand must go with it, even though the hand is still free to move on its own.

This is something usually practiced by 3-D character modelers who create video games and animated motion pictures. Fortunately, After Effects gives us some pretty powerful tools to accomplish kinematic motion on two-dimensional characters that can really fool the eye!

For these examples, I've taken a single stock image of a skeleton that had an alpha channel already created, and I tore it to bits! You'll find the Photoshop image,

SkeletonSmall.psd, on the DVD, so you can see the many layers that were created out of this original image (Figure 5.28).

o a o

Lavers "-giMMit^l^ttoNH^^^

' Naiirad l-^J Qpaoty | MQfc

Fttt|MOK J|

01 Sfcull

Ui

m

^J Oi

is

93 L>pp«T To"so

1*

^ 94 Left Ami Upper

1*

^J 05 Lfft Arm Lower

IS

^J 06 Left HarwT

IS

^J 8? Bi§h: Aur uppe'

IS

OS High: Arrr Lower

IS

99 High: Hand

LI

IS

11 Lonet Sp ne 1

IS

12 Lowe»Tor*e

. -3, a: ©Jul si*:.

Figure 5.28

Open the skeleton Photoshop file to examine how the layers are created and how they go together.

Figure 5.28

Open the skeleton Photoshop file to examine how the layers are created and how they go together.

Create a new project file in After Effects, and import the file SkeletonSmall.psd as a composition to retain the layer information. Open the composition from the Project window, and edit the Composition Settings to resize it and allow more side-to-side motion when animating the layers.

Determine a central point of the body, which all the other parts can link to and move naturally. I've chosen the upper torso layer, where the arms, neck, and spine can connect to it. From this point, we will work out from the upper torso through all of the extremities. You may want to at least peek at the After Effects project file, Skeleton_ Practice.aep, on the DVD, to follow along until you get the hang of what we're doing.

The Knee Bone's Connected to the Leg Bone

Connecting the layered pieces will require important techniques: proper positioning of the Anchor Points and parenting the layers. The Anchor Points need to be located on each layer where the swivel point of the joint would naturally move. This is where it will be "connected" to the layer to which it is parented.

Moving the Anchor Point on each layer requires you to open each layer in its own window and zoom in so you can really see what you're doing! Drag the Anchor Point to the joint or nearest connector point where it can swivel around (Figure 5.29).

Composition. SkeietonSmall Comp 2 1 fi | 015kui t | x ' ►

■< f1

fylf 05! lOf

ISf 2 Of

25 f 0i:p0f

Ijj 0:00:00:00 [JJ 0:00:01:04

A0:00:01:05 Vkw 1 Masfcs 3 Render

H JOOM j » Id 0 00;00;00 I® i^JBEi

Figure 5.29 Zoom in on each layer and reposition the Anchor Points where they connect with other pieces.

Figure 5.29 Zoom in on each layer and reposition the Anchor Points where they connect with other pieces.

To "connect" the layers, we use the Parent option on the Timeline. This doesn't really completely connect the layers, but it does allow you to move the parented layer and have those layers attached to it move with it. Parenting also allows you to rotate layers, and they will rotate around the Anchor Point that you positioned at the joint, so they will appear to be attached to the parented layer.

Let's look at a smaller segment to further understand how this works. Hide all of the layers except for the two left arm layers and the left hand layer. With the Anchor Points at the joints connecting to the preceding layer, select the preceding layer as a parent layer using the Parent Layer Selector on the Timeline (Figure 5.30). Rotate the lower arm layer and see how it moves at the elbow. Rotate the hand layer, and it should bend at the wrist. Move or rotate the upper arm layer, and both the lower arm and hand will move with it.

2 I Composition SkeletonSmali Lcfnj 2 \ '

• IB,;:; 0.00:00:06 lUffl ■ fr: FL.il ivi™ • "HhJJ A

Figure 5.30 Experimenting with a small section of the skeleton will help you understand the physics of the motion and how the layers work together.

With everything parented in all the way to the upper torso layer, you should be able to move the layer, and the whole skeleton will move with it. If you rotate the upper torso slightly, you will need to rotate the spine segments, lower torso, and legs to bring the feet back down to the ground (Figure 5.31).

Figure 5.31 Rotate the upper torso layer, spine segments, and lower torso layer to see how twisting the body makes the rest of the limbs react.

Making adjustments to all of the limbs from this position, you can start to emulate graceful movements (Figure 5.32). It's like combining a stop-motion wire figure animator with a puppeteer. With a little creativity and finesse, you can really have fun animating your skeleton character!

In some cases, you will need to adjust the length of a foot, arm, or leg segment to give the appearance of upward or downward motion in the Z-axis—even though there is no Z-axis present in a two-dimensional animation (Figure 5.33).

Figure 5.32

Some experimentation and practice will help you get the feel for putting your character in motion.

Figure 5.32

Some experimentation and practice will help you get the feel for putting your character in motion.

1, Timeline

: Skeleton Small Comp 2 x^*

OrQP^OO.QG (29.97 fps> [B] *

j

"I00'

02 f

04f ■

3

, «

m i

w 1

TT

• Oil •: a

J * Layer Name | # \

Par em

Ll

i

9

'>TTi 3 oi skuii ^ /

® 2 02 Kec,

----

nm

D> O 2 is 02 IMeck J3- /

© -. IH Uppei

3B h

m u

Q 1 Nona

i

4 v ►

■ H>]ht Rotation ■ > :I0 2 "

e

<

i

Hi

t> A 04 Left Arm Uppe /

® 1 3. 03 1IPPB

33 h

9

pQs 05 Left Arm Lowe Jp- /"

B 4. 04 J(1*J.' ■

1

m

^d6 v> 06 Left Hand J&- /

' 5 05 .»J\ A'v ■

j

l>ni7 07 Right Arm Upp /

® 1 3.03 Upper •

1

9

t>na 5 08 Right Arm Low /

B 1 J, 0?f!tahlAI»

1

»

-i 09 Right Hand /

'i. 6 oa ftighi

Al-i ■

1 1 1

HH

Kt 10 ^^SJHE^^^EB S

® i. 03 Upper 1 •

li_ _ ..i

- fct Rotation 0 i +1.5 '

t

>

m. WM

Kt ^ >

O 10. 10 low

!Fl*. (

RfSffe Rotation I! * +S.7"

jl

b

>

#

t> _ 12 12 Lower Torso ^ /

B 11. U Low.

as h

1

,2, -.MI^fK. ✓

® i 12. 12 Lorn f 15 " 1

OB h

u

Figure 5.33

Scale the length of a segment to adjust for the lack of a Z-axis in a two-dimensional animation.

Figure 5.33

Scale the length of a segment to adjust for the lack of a Z-axis in a two-dimensional animation.

Kinematic Animation Example

Let's make a simple animation that moves every layer in our skeleton, simply by rotating layers with kinematic motion. Using the principles previously covered, we'll build this animation key frame by key frame, instead of layer by layer.

Because of the possible variations in building your model, it would be best to use the file Skeleton_Practice.aep from the DVD. The parent layers have already been applied, so all you have to do is follow the settings in Table 5.12 and study what is happening in each layer's rotation.

Table 5.12 Simple Kinematic Skeleton Key Frames (All in Degrees)

Layer Transform Rotation

00;00

00;06

00;08

00;10

00;16

00;23

00;25

00;26

01;04

01 Skull

-0.8

+11.1

+0.5

-14.3

-1.9

02 Neck

-0.3

+11.7

-3.1

-16.5

+0.8

03 Upper Torso

+1.1

-10.2

+4.7

+17.5

+1.0

04 Left Arm Upper

+0.0

-13.9

-17.5

-4.6

-0.3

+23.3

+15.5

-1.1

05 Left Arm Lower

+6.2

-35.5

-58.0

-3.3

-14.6

+5.2

-7.1

+8.6

06 Left Hand

-7.4

-16.9

-9.7

07 Right Arm Upper

-0.9

-22.9

-29.2

-23.7

-6.6

+11.5

+3.5

+0.2

08 Right Arm Lower

-5.0

-4.0

-10.0

+10.0

-1.4

+39.6

+48.4

-8.2

09 Right Hand

+5.2

+27.8

+41.2

+24.5

+12.7

10 Lower Spine 1

+1.1

+2.5

-3.7

-5.7

-1.3

11 Lower Spine 2

+0.0

+5.7

-4.1

-5.0

-1.3

12 Lower Torso

+1.4

+13.0

+5.9

-1.6

+5.2

13 Left Hip

-5.6

-8.7

-9.4

-8.1

-15.2

-20.7

-15.8

-4.2

14 Left Shin

+2.8

+6.5

+7.5

+9.9

+23.1

+48.7

+35.5

+0.1

15 Left Foot

-6.1

-15.0

-9.2

-18.6

-45.2

-52.8

-43.1

-4.7

16 Right Hip

+2.2

+10.5

+16.2

+9.7

+2.6

-5.1

-0.5

+4.7

17 Right Shin

+0.0

-43.6

-55.8

-35.1

-3.2

-6.4

18 Right Foot

-11.0

+26.9

+25.3

-3.5

-3.6

-8.9

-5.1

Note: If you would like to see the completed After Effects files in their entirety,open Skeleton-Projectl.aep and SkeletonProject2.aep on the DVD and compare them to the projects in this section.You can also view the completed QuickTime movies of the completed animations.

Details in Kinematic Animations

Subtle movements and fine details are what give realism to figure animation. Although this skeleton doesn't have individual moving fingers and toes, you can still apply movement that emulates a real figure, just by keeping constant motion present in small amounts.

The effects of kinematic motion are most noticeable when you are applying them to shoulders or hips, where there are many intersecting points. The tilt of a shoulder will cause necessary adjustments of the head and neck, as well as of the arms and the lower spine. Something as simple as crossing the arms or shifting to one foot causes a ripple effect throughout the entire body—as in SkeletonProject2.aep, the sample animation located in the Chapter 5 project folder on the DVD.

When creating animations that require precision in movement, you will need to use rulers and guides to keep track of where your character is moving. While you are concentrating on the upper body, the legs may shift out from under you, and before you know it, you could end up with a floating ghost with dangling legs!

While shifting the weight of the figure to one foot, you can see how much the rest of the body is influenced by this move (Figure 5.34). When the leg crosses over, the hips swivel upward, the spine adjusts to keep the head and upper body level, and the body comes to rest centered over the standing leg.

Figure 5.34

Using guides is very important to track your motion and make sure everything lines up correctly.

Figure 5.34

Using guides is very important to track your motion and make sure everything lines up correctly.

Photoshop Secrets

Photoshop Secrets

Are You Frustrated Because Your Graphics Are Not Looking Professional? Have You Been Slaving Over Your Projects, But Find Yourself Not Getting What You Want From Your Generic Graphic Software? Well, youre about to learn some of the secrets and tips to enhance your images, photos and other projects that you are trying to create and make look professional.

Get My Free Ebook


Post a comment