No. 67, More About Animating 4-legged Animals

Four-footed Movement

It is worth pausing here to talk a little about animating animal legs.  You might suppose that if you've seen one four-legged critter moving, you've seen them all, but this is far from true. Once I assigned the animation of a little cartoon goat to one of my animators on a children's game.  She did a perfectly acceptable job on it and I approved it, but a week later I happened to see a goat walking and was struck by how the goat appeared to be walking tip-toe, like a woman wearing 5-inch heels and having to bend her knees slightly.  That's how they walk! It would have been a charming touch to have included in the scene.

In my last post I mentioned a book, Dog Lomotion and Gait Analysis, by Curtis Brown (Hoflin Publishing) that is a favorite reference for this kind of thing.

Dog Locomtion and Gait Analysis, by Curtis Brown

If you are interested, I find that this book is still available.  I also see that there are now some others on the same subject, but I cannot speak about them.

Even within a single species, not all animals move alike.  That is especially true of dogs, which have been bred to take so many different forms and proportions. Tall dogs, for example, tend to use the pace (moving both right legs forward together, then both left legs) instead of the trot (a front leg moves forward with the opposite rear leg).  Terriers will never move like greyhounds, even walking and standing.  The book goes into all this and more in great detail--in fact, probably in more detail than one would ever need.  But if I were animating a Lady and the Tramp or a 101 Dalmations today, I would certainly want this book at my desk.

A typical double-page spread from the book.

 I discovered Dog Lomotion by chance, and I have had my copy for many years.  In fact I wrote a review of it for Animation World Network back in 2000. Here is the link if you would like to read that review.

Of course now there is a wealth of movement reference of animals on the internet, most of it free as in YouTube, and I recommend that you take advantage of it whenever your assignments call for some realism in animal movement.

Elegant Anatomy

Let me draw your attention to one particular detail of four-legged anatomy that I think is common to all digitigrade mammals: the pastern.  Digitigrade means walking on the toes, as distinct from plantigrade, which means walking on the flat of the foot. (Bears and humans are plantigrade animals.) Most notably,  horses and dogs and cats have the pastern, as do all their close relatives.  It is a flexible joint in both front and rear feet that allows great energy to be suddenly released in running, and visually it is an animator's delight.

In the drawing above, from left to right, you can see the changes in the pastern joint of the front leg of a dog.  First it is compressed as it bears the full weight of the animal and propels him forward; when it is released and carried ahead it makes a sudden and beautiful flip, dragging the foot behind it; then as the whole leg is brought forward the foot drops down from the pastern, ready to make contact with the ground; and finally, pressure on the foot reverses the angle of the pastern once again.

Of course this all happens very quickly as the animal moves, but to include this action in the animation of dogs or other animals always adds a snappy elegance to their movement, and it is a prime example in nature of what the great animator Art Babbitt called "successive breaking of joints." You can exaggerate it; you can have fun with it; but you should never leave it out.

Here are 4 consecutive drawings from my fox's trot that show the pastern working.

Next:  Thought Process and the Animator

No. 66, Creating a Four-legged Walk Cycle

FOXTROT

A short while back ( Acme Punched posts No. 60 thru 62) I showed you my approach to creating a walk cycle for my character Albert.  Now here is a walk cycle, or rather a trot, for the little fox character.

First, a bit of re-design was in order.  I made the original model sheet without much attention to the real anatomy of a fox.  This is a cartoon and you can do that, but he does walk on all four feet so I have now decided it would be good to have him move something like a real fox, and for that, he has to be constructed a bit more like a real fox.

In the original model sheet, above, he is rather swaybacked and holds his tail erect.

The revised design makes his spine arc upward a little, as in real canines, and shows him holding his tail almost straight out behind him when moving.

 The Animation

Once again I wanted to try something I had read about but had never actually done: to animate the head, body and tail before doing the leg animation.  This is effective in animating dance and other controlled movement such as sword fighting.  Disney animators have used the technique in animating such semi-realistic creatures like deer (Bambi), though others actually did the reverse, animating the legs before the body. (I would cite a reference for that, but can't recall exactly where I read it.)

Anyway I thought it might work on my cycle of a fox trotting.

This was the first test.  It was made using just three drawings, with the middle drawing favoring the highest one in its spacing (see Fig. 1). I thought the rhythm was fine, but since the fox will sometimes be quite small on the screen, I decided it was too subtle.

Now for a broader movement, in which I simply let his body drop down farther.

At the time (we will come back to this) I thought it was fine, and went with it. Here is the spacing.

Then I was ready to add in the legs.  This is a basic canine trot.  I referenced a favorite but little-known book of mine: Dog Locomotion and Gait Analysis, by Curtis M. Brown.  Brown is not an animator but a dog breeder and dog show judge, but the sequential drawings of the gaits of various breeds are a gold mine for anyone interested in how dogs move.

Here is the test.

Hmm.  I sort of liked it when I saw it, but...something was not right.  Can you see what is wrong without reading further?

If you said that the head was moving too much, you would be right.  I had lowered the head along with the torso.  It is the same as it was in the second version without the legs (see Figure 2 again also), but somehow it was not apparent to me until I saw it all put together.

Solution?  Leave the torso as it is but just space the head much closer to the other heads.

Now it is working right.  Many animals avoid movement that bounces their heads up and down very much, because either they need steady vision for pursuit of prey or to detect danger.

One more thing I thought to do was to see if I could vary the speed--make him move faster--without removing any drawings.  (He may have to trot quickly to keep up with Albert's brisk walk.)  The slow speed is 8 drawings on 2's, or sixteen exposures, thus: 1, 1, 3, 3, 5, 5, 7, 7, 9, 9, 11, 11, 13, 13, 15, 15.  The numbers in bold are the lowest position.  The obvious thing to try here is to see if it will simply work on 1's: 1, 3, 5, 7, 9, 11, 13, 15.  But it looked too fast and also jerky, so I am not even showing it to you.  Although it does not always work to have some drawings of a walk cycle on 1's while others are on 2's, because of the danger of "slipping" against the steady movement of the background, I decided to try this: 1, 3, 3, 5, 5, 7, 9, 11,11, 13, 13 ,15.  In other words, I dropped the second exposure on drawings 1, 7, 9, and 15--just four frames fewer, but look at the result:

It seems to work!

Next: More about working with 4-legged characters!

No. 62, A Walk Cycle for Albert, Part Five: Side View

 Solution to "Mystery Change"

In the last post (No. 61), I challenged you to find a difference in timing between the two versions of the walk cycle.  No one took me up on it, and I admit it was a subtle detail to find amid everything else that was going on in the cycle.  But the answer is: I changed the timing of the right arm (the one holding the bag).  In version 1, as the bag comes forward and then reverses direction to recede again, the movement seemed to me to have a stabbing aspect to it; that is, it took no time and no effort to reverse direction.  I thought this was inappropriate for a bag that might weigh 100 pounds or 45 kilograms.

I therefore took a look at the spacing of the drawings.  As the bag comes forward, it has an appropriate cushion-in.  The chart below shows the relative positions of the seam at the front of the bag.

But as the bag reverses direction, the drawings were not spaced so as to give a good impression of the cushion-out (the spacing that indicates that an object starts out slowly and accelerates.)  The next chart shows both the old and the improved spacings.  Again, it is the seam on the bag that we are following.

The original spacing is shown in red, on the left.  Final spacing on the right.

I think if you will now go back to post no. 61 and carefully compare the two versions, you will observe more of a slow-down and hesitation between the forward and backward movements of the bag.  It is more like the compression and release of a spring, as it should be, rather than like something bouncing.

Translating to the Side View

The obvious way to begin this translation of view is to construct the first image over the corresponding one of the other.  On my drawing board, that looks like this:

The front view showing through on my backlighted animation disk.

In a case like this, which is just a rotation on the Y axis, as the 3D-ers would think of it, many measurements can be directly applied from one drawing to the other.

Here are the two images separated, with a few points of congruence highlighted:

Showing where the top of the hat, the eyebrow, the shoulder seam, the top of the button and the bottom of the body mass coincide in both drawings.

Some things, of course, require adjustment.  Mainly these are the parts that project forward or backward in imagined space from the plane of the torso.  Thus the left hand appears larger in the front view to create the illusion that it is closer to the viewer, and the left foot is drawn smaller to show that it is farther back.

It should be emphasized that a walk cycle--or any animation, for that matter--should be designed with the perspective of its layout or background in mind; note the converging lines like floorboards on the drawing at right above, indicating the plane upon which the character is walking.  If you animate something without regard for the perspective and scale of the layout, you may be wasting time and work.  This should be considered even if creating something such as a gif animation meant to occupy the featureless expanse of a webpage.

Creating other angles wherein the viewpoint is raised or lowered is also possible, but here more sophisticated drawing skills are required to extrapolate from one to the other.

The same pose from a high angle, 3/4-front view.

I once was called upon to animate a character running while the camera swooped all about him--something a 3D animator of today would, admittedly, be able to do easily.  Yet once I had done a version of his run cycle from one viewpoint, I was able to work out all the other angles, and the whole thing worked very well.

Here is the first pencil test of the side view walk cycle:

I thought it worked pretty well, and it was fun to watch, yet something was not quite right for the walk of a man traveling a great distance.  Finally I decided that his stride was a bit too long; he is reaching a bit too far with each step.

So I shortened his stride by this much:

The erased images in red brackets show the original reach of his stride.

Here is the second test, incorporating the somewhat shorter stride along with a few other adjustments to the foot and leg positions in all the drawings:

I like this second version; except for details and cleanup, I am calling it done.

Your comments and questions are always welcome, and if you like what I am doing here, why not click on the Join This Site button and become a Follower?  That way you won't miss any posts, and I promise you many more to come!




Coming soon: Walks for Albert's Companions, a Fox and a Goose--two short-legged characters who must keep up with Albert's rapid pace!

No. 61, A Walk Cycle for Albert, Part Four: Front View Final

I am going to present two versions of Albert's walk made this past week.  The first is about half cleaned up, with not all of my planned changes yet done.  The second is the final cleanup.  Later in this post, I will explain why I am including the half-finished version as well as the final.

The half-finished version. Here, some of the drawings are still in blue pencil but most of the planned changes are in.

This is the final pencil test; the drawings are all done in graphite pencil now and are ready to be scanned for digital ink-and-paint.

Cheap Trick Department:
When doing cycles such as this, one is constantly comparing the first half of the cycle with the other half; otherwise, the movement will not look balanced. In this case, drawing 1 (the right foot contact drawing) is more-or-less a mirror image of drawing 15 (the left foot contact drawing.)  Thus, each drawing in the cycle has its mirror counterpart.  With 14 drawings to track in this way, I have found it useful to give the drawings an alphabetic designation as well as its numeric one.  So drawings 1 and 15 are both also "A"; drawings 3 and 17 are both "B", and so on.  In this way it is easy to pull out both the drawings marked C or D or whatever for comparision to one another.

Changes made since the version shown in Post No. 60:
--More change of scale front to back.  That is, when Albert's foot or hand is closer to the camera, it is more obviously larger than when it is at the back, farthest from the camera.  This change of scale in what 3D animators call the Z axis can add depth and drama to a scene, even when the character's body remains a constant distance from the camera.  Opportunities to utilize this enhancement should not be neglected.

--Left arm animation.  As mentioned in No. 60, I was unhappy with the arc of the arm as it came forward.  This has been fixed.

--Shorter pants legs, with socks showing.  Shown only in the final.  Albert's socks are red, so there will be an amusing flash of color there.  Also I am simply complying with my own model sheets for Albert, bringing him on model.  The pants legs also are animated as a follow-through to the leg movement but this is rather subtle.

--Precise drawing.  Cleaning up the images in the same order in which they were drawn as roughs (extremes, then breakdowns, then inbetweens), everything has been tightened up.

--Foot slippage.  This could come under the heading of precise drawing, above, but in walk or run cycles it rates its own category.

Foot Slippage chart on drawing 17.

In doing the rough animation, I had just "eyeballed" the foot positions, but when it came time to clean the drawings up, I scrutinized them closely and found it useful to make this chart.  The lines represent the back of the heel on drawings where they are in contact with the ground.  Note the ghost images showing where the feet originally were in this drawing.

--Mystery Change ???  There is one other change I made here, and I challenge you to find it by comparing the Half-Finished and Final pencil tests above.  No new drawings were added, but something I haven't mentioned has been re-timed.

Can you find it?  I will post the answer next time, but I would like to hear from anyone who can find the change.  Moreover, can anyone tell me why I made this change?


Next: We Rotate Albert 90 Degrees and See His Walk from the Side.

No. 60, A Walk Cycle for Albert, Part Three: The Full Test

In addition to filling in all drawings for this walk cycle, this week I have improved the readability of these pencil tests.  Because I often do my rough drawings in blue pencil, the tests done in Toki Line Test software have been of such a low contrast that by the time they have been rendered as Quicktime Movies, they are hard to see, especially if there are multiple levels.  Now I have greatly improved this by exporting the drawings from Toki as jpegs, then adjusting their values in Photoshop before importing them once again into Toki Line Test.  I think you will appreciate the sharper, more high contrast result.

This test is now working in most ways.  A good walk cycle includes many details of movement besides just moving the feet and legs and swinging the arms. Here are some things I included in Albert's walk:

Rhythmic vertical movement. Does the character rise up or drop down on the passing positions, and by how much?  I have Albert rising up enough to be noticeable.

Shoulder action.  Albert's upper torso rotates in opposition to his hips, but his right shoulder is kept highest at all times because of the load he is carrying on that side.

The legs and feet.  They are working well.  Just before each of the contact drawings I inserted a little kick; he throws his foot out past the point of contact for one drawing (2 frames) which adds a nice confident snap to his walk.  It has an impact more felt than seen. Here is the detail showing that:

Two drawings before contact.

One drawing before contact; the foot is thrown forward, beyond the contact point.  

The contact drawing (his right foot.)

Head action.  I have made his head tilt to alternate sides on the contact drawings and to be verticle--untilted--on the passing positions. This will mean that in a side view of the same action, his face will be partially hidden by his hat brim when the right foot makes contact (see drawing above) but I have planned for that.

The swinging arm.  This works pretty well but I don't like the way the arm comes forward.  It should swing out farther rather than in as I have it now.

Follow through actions.  [1] After the contact drawings, the belly descends and delays coming up for a couple of drawings, giving him an appropriate heaviness.  I want to refine this some more.  [2] When the left hand reaches its full extent at the front it flips up.  [3] The hatbrim flips up and down a little as he bounces along, but that needs more refinement also.

These details and others can be thought about and added in now that the basic elements of the walk are in and approved.  Although it is possible to suggest secondary and follow-through action during the first pass through the animation, usually they will need some adjustment, and it is perfectly alright not to put them in at all until the first pass is complete.  A walk cycle like this presents a lot of challenges, so it is all-important to get the basics right first.

For an exhaustive look at animating walks, see Richard Williams' book The Animator's Survival Kit.


Next: Refining the Details of the Walk

No. 59, A Walk Cycle for Albert, Part Two: Point of View

A Different Point of View

In thinking about this walk for Albert, I have most often pictured it from one side, the standard view for getting the most out of your drawing cycle.  In 3D terms he is walking along the X axis, but the camera stays with him and matches his speed so that he stays centered on the screen, while the background can be seen slipping past.

But even though I want to show this profile angle, there is a problem in designing it in this way because of the sack of grain he is carrying; its great weight forces him to walk assymetrically, and from the side this is very hard to visualize.  Here are a few sketches showing my struggles with this problem.

I seem to remember reading of an animator (Frank Thomas?) advising that if you are having trouble drawing a character from the camera angle, to first draw it from a more obvious angle, then extrapolate back to the original angle.  In other words, draw it first at an angle  from which you can understand the proportions and mechanics, and then rotate it in your mind to whatever it must be.  This is difficult but it is a skill most long-time pencil animators have developed.

So in this case, I decided to try looking at the walk from the front:

Right contact position.

Immediately I could see that this was the way to go.  Here are the other three key drawings for the cycle.

Passing position.

Left contact position.

Passing position.

And now I have a first pencil test made with just these 4 drawings:

The cycle is designed to last 28 frames at 24fps, a bit longer than usual.  Also I am putting the emphasis on the contact positions, so in the test, instead of exposing the 4 drawings equally, seven exposures for each, I gave the contact drawings 8 exposures and the passing positions only 6 each.  It still adds up to 28 frames, but the rhythm more nearly matches what I want the final result to be.


Next: The Test from the front, with all drawings filled in.

No. 58, A Walk Cycle for Albert, Part One: The Brief

If you have been following this blog at all, or if you go back now and look at some of my previous posts, you would have seen or will see a lot of my two human characters, a man and woman I call Albert and Victoria.

The long sequence I have been detailing for the blog has them facing each other, mostly standing in place.  But there are other planned scenes in which Albert is doing a lot of walking.  Mostly when he is walking, he is encumbered by a heavy burlap sack of grain under one arm.  Sometimes the full-grown goose is being carried under the other arm.

An early concept drawing of Albert walking.

Now that I am at the actual point of animating his walk, I want to pull together all the thoughts I have had about it as I worked with Albert in other ways.

Here is what I know about Albert and his walk:

• He is a big man, overweight but solid rather than soft, and he is very strong.  
• The sack of grain may weigh 100 pounds [45 kg] but it is not too much for Albert to carry under one arm.
• He has miles to walk, so his walk will be deliberate and measured; something he can maintain over a long period of time.
• He does not mind hard work, so to walk a long way with such a load does not in any way make him unhappy, and he is by nature a cheerful and optimistic man.

This is the kind of thinking that should go into the planning of any animation, but sometimes novice animators forget this when it comes to walks.  They think, I'll just sit down and animate my character walking, because they want to see it, but there really should not be any such thing as an all-purpose walk.  If a character is crossing a room, it is for some reason.  It will affect his or her posture, as well as the speed and style of the walk. His entire state of mind is important, too; whether he is in haste, is anxious or relaxed, is fearful or self-confident, is fatigued or energetic.

Perhaps a walk must be done even more carefully than non cyclic animation because it is a cycle and will be seen in repitition, giving the viewer time to study it that is not the case with a one-off.

I have been thinking about Albert's trekking walk a long time, and now I am ready to animate it.


Next: Choosing the Best Point of View for Designing the Walk