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### 27.18.7 - Transition Morphing - Nuts and Bolts

Now that you've seen the transition morphing effect in operation, let's briefly go over what you did from a more specific, technical point of view.

You placed Control Points. These actually consist of two elements, start and end points. These specify an exact amount of movement for the point of the image which is exactly under that particular Control Point. Areas of the image which are not directly underneath a Control Point move in such a way as to agree with all the Control Points nearby; the closer a Control Point is to a portion of the image, the more the image will move in a manner similar to the motion of that Control Point. Control Points which are very far away from a location on an image will have little or no effect on that location.

You also placed Links. These are lines that go between two Control Points. They suggest to the software that no image information should cross the Links; while Control Points alone may not exactly control an area, the combination of Link and Control Points can create almost any needed distorting motion that is reasonable.

We brought up an interesting issue in the last paragraph — what kinds of motions are reasonable and what kinds are not? It is a fact that the kinds of motion that can be specified with Control Points and Links is nearly infinite, but not all of them are reasonable. Morph has to attempt to keep the motions you specify for the image surface connected, so that portions of the image flow together in a natural manner. It is possible to specify motions that cause tearing or folding of the image, though, and normally this will not be what you want.

As you attempt more complex motions, you'll begin to encounter these situations. To solve them, you can either eliminate the offending motions or try to be more specific in those regions by adding more control points and links.

Note that when we were discussing Links earlier, we said they suggest control. This is because some types of edge combinations are impossible, such as where two Links cross each other, and Links in those situations will either be ignored or will cause image tearing and/or folding. Odd things also happen when the vectors specified by Control Points cross each other. A good rule of thumb is to have as few as possible crossing vectors or Links in any morph you attempt to do.