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by Christopher, 2010-01-21 02:33:43
Tags: animation photography science how-to javascript
A zoetrope is a low-tech device for creating animation. The classical zoetrope consists of a cylinder that you put a reel of frames into. When the cylinder is spun, you see the frames of the reel in a looping animation. Today, the zoetrope is probably the most famous 19th-century animation toy. It's much more versatile than a phenakistoscope, because you can change out the reel, and it's much simpler to make than a praxinoscope, because it doesn't involve any mirrors.
As a volunteer exhibit hall interpreter at the Boston Museum of Science, I've discussed the zoetrope with visitors for several years. One common question is, can I make my own reel? The answer is yes, but it's harder than you might think. I tried to do it myself using photographs that some woman and I took one day, and I learned a few things about the process. In addition to using still photographs, you could also use frames of a video, or draw the frames by hand. Most of these tips apply to any method you use.
It's very important to realize that not every action works well for a zoetrope. Most zoetropes admit only 12 frames. The speed of the action depends on how fast the zoetrope is spun: typically this is between one and two revolutions per second (12-24 fps). There are two reasons it needs to be this fast: a hand-spun zoetrope will spin down in a short time if it's started slower, and zoetrope animations don't look good at lower framerates. Unlike the animations on this page, zoetropes rely on your persistence of vision between frames. Below 12 frames per second, the "flicker" effect obscures the illusion of motion.
These controls will affect the speed of all the animations on this page. Notice that many of them get very hard to follow at more than 24 fps.
So you need an action that looks okay repeating one to two times per second. Simpler is better. Popular animations include people and animals walking in place.
Make sure whatever action you choose makes sense repeating. In particular, your last frame should not be too different from your first frame. For this dance step, the subject's position was a little closer to the camera at the end of the action than at the beginning, but her pose synched up well, so I was able to make the loop match up by removing the background, then scaling and shifting the frames with respect to each other. If you look closely at her left foot in the adjusted frames, you'll see it moving steadily upward throughout the sequence.
This is the only animation that I've actually made into a zoetrope reel so far (see below). It's pretty good, but I would like to redo it with a little less motion: two steps instead of four.
For photographs or video that will be made into a zoetrope reel, a tripod is highly recommended. However, it's possible to do some stabilization after the fact in a grahical editor. Using The Gimp or what have you, load all 12 frames into different layers of a single image. Use one frame as a reference, and by varying the transparency of each layer one by one, you can align them with the reference frame. The difference is shown in these two animations. In this case, a brick background was very helpful for alignment. There's still a little jitter, but that would hardly be noticable on a typical-sized zoetrope.
Seems like a great gift idea for a loved one, doesn't it? A zoetrope and a reel of you mouthing a secret message. Well, I won't say it's impossible, but it's hard. Keep it extremely short. I haven't experimented too much with this, but I think you really need to plan each frame very precisely, to make sure they hit the most important facial motions. If you just used the frames of a video, I don't think it would work well. In this example we tried "I love you", but the "I" doesn't show up well because we didn't plan a frame of a closed mouth in between it and "love".
Also remember that the zoetrope is much smaller. You will probably need to zoom in very tightly on your face in order to see enough detail of the mouth. For stabilization with this animation, I chose to stabilize the subject's face instead of the background.
Okay, so you've got your 12 frames ready. You just need to print them or draw them onto a strip of paper the right size. If you don't have any blank reels that came with your zoetrope or anything to show you the proper frame size, start by putting some regularly spaced vertical lines on a strip of paper and load it in. If the lines look stationary when it's spun, they're spaced correctly.
Should your frames be sequenced left-to-right or right-to-left? If the zoetrope will be spun counter-clockwise, order them left-to-right. If the zoetrope will be spun clockwise, order them right-to-left (ie, backward). Most right-handed people will naturally spin it clockwise, so if your zoetrope is spun by hand, I recommend going with right-to-left. Of course if your animation is the same forward and backward, it doesn't matter.
Just like the frames of a 35mm film reel are stretched vertically, the frames of a zoetrope reel should be stretched horizontally: when the zoetrope is viewed, the frames will be compressed horizontally. The amount of compression doesn't depend on the speed of the zoetrope, but it does depend on the distance of the viewer's eye from the zoetrope cylinder. If the viewer's eye is right up against the cylinder, there will be almost no compression (so the compression factor will be 1), and if the viewer is very far away, the compression factor will be almost 2. So it's impossible to stretch the frames by the right amount to compensate for the compression in all circumstances.
I chose to stretch by a factor of 1.5, which is the appropriate amount of stretch if the distance from the viewer's eye to the outside of the cylinder (x) is equal to the diameter of the cylinder (d). If you want to assume a different viewing distance, use a compression factor of (2x + d) / (x + d).
A figure in a zoetrope reel can smoothly move from one frame to another. This is an advanced technique, and something unique to zoetropes (and phenakistoscopes): you can't do it with film or cartoons. The tricky part is that there will not be exactly one figure per frame. Say that you have 12 frames, which advance from left-to-right (counter-clockwise rotation). If the figure moves one frame to the right per cycle, it will appear on the reel only 11 times. If the figure moves one frame to the left per cycle, it will appear on the reel 13 times.
I don't have any reels that demonstrate this technique yet.
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