Morphing Basics

In order to do this, you tell Easy Morph what parts of the object(s) in the first image match the object(s) in the ending image.

That is done using control elements that are made of matched pairs of "polylines". Polylines are lines made up of one or more straight segments. These lines are placed in the morph in matched pairs; each polyline in the start frame is matched by a polyline in the end frame.

The matching polylines may have different numbers of segments; for instance, the start frame polyline might have three segments, and the end frame polyline might have 20. The number of segments has no effect on how the lines match over their length, they only affect where the polyline lies on the image.

This is very important to understand: Polylines match over length, not by the position of the control points that divide them into segments.

Polylines are very easy to place. You simply click a few times in one frame using the left mouse button to place the starting polyline, then click a few times in corresponding locations in the other frame using the left mouse button to place the matching, ending polyline, and then you finish the polyline by clicking once with the right mouse button. You can begin in either frame; in other words, you can place the end frame polyline first, or the start frame polyline first, it doesn't matter.

In order that your morphs come out well, there are a few basic techniques you'll need to use as you create your control elements made from pairs of polylines. We'll show you what each one means in detail, but for the moment, here they are, all together:

1. Make sure that each polyline you create starts and ends at a matching feature point.
2. Make sure that when the starting polyline is clockwise, so is the ending polyline, and vice-versa.
3. Never allow polylines to cross in an image (this is easy to see.)
4. Never allow polylines to cross in time (not always obvious, requires care.)

Here are the two images we'll be using to demonstrate these points:

Rule One:
Match Feature Points

Looking at the above images, some useful matching feature points are identified by matching colored arrows.

For instance, the top center of the edge of the eye in both images is identified with an orange arrow. These points match in the sense that we want them to correspond to each other during the change from one image to the other; in other words the top of the girl's eye should transform into the top of the frog's eye.

To achieve this, a control element must be placed in the project such that the polylines start and end at matching feature points, and cover matching paths between the feature points. Here's our first one, switched into editing mode so you can see the control points along the polylines:

This control element, or pair of polylines, meets our criteria of starting and ending at matching feature points. These are the points identified by the orange and light blue arrows.

Terminology:

Control Element: This is the pair of polylines, one in the start image and one in the end image, treated as one "thing."

Control Point: These are the points where you click; they will be identified in edit mode with a square box along the polyline.

Segment: This is a part of a polyline that lies between the control points

Rule Two:
Match Line Direction

If one polyline had been placed starting at the light blue location and ending at orange, and the other was placed starting at the orange and ending at the light blue, the morphing engine would try to "flip" the image area the line covers during the morphing process, which would look terrible. The red arrows show the order that we put the line segments down in, both clockwise:

It doesn't matter if they are clockwise or counter-clockwise, they just have to be placed in the same direction. Sometimes the idea of clockwise/counter-clockwise may not apply, as the lines may follow complex paths. The idea still applies - match the directions of the starting and ending polylines. A little practice will settle the idea into your head. Lines must be placed in the same direction.

Rule Three:
Never allow polylines to cross in an image

This one is pretty much self-explanatory, once you've looked at the above image. The new pair of polylines cross the first pair in both frames. You can't let them cross is either frame, much less both of them. Look at the image and commit the idea to memory: If polylines cross, your morph is going to come out badly.

Rule Four:
Never allow polylines to cross in time

In the above image, the red line is the first line we placed. The blue line, in edit mode so the control points are visible, is the new line.

The new line is one one side of the first line in the start frame, above and to the left.

But in the end frame, the new line is on the other side of the first line - below and to the right. That means that over time, as the morph is generated, we are telling the morphing software that we want the region defined by the new polyline to cross the region defined by the first polyline. In other words, these regions would cross in time.

This kind of cross will produce a "tear" in the image surface, visually disturbing and highly undesirable.

Polyline Placement Tips

• You can put the currently selected control element into edit mode by clicking on the tool at the bottom of the toolbox with the four arrows in a cross:

• You can move any control point by clicking on it with the left mouse button and dragging:

• You can move an entire polyline by clicking on it with the right mouse button and dragging:

• You can select any polyline by pressing and holding the Ctrl key on the keyboard. and left-clicking near any control point on the polyline: +

• You can also select the next or previous polylines of those in the control set by pressing the left or right cursor arrow keys on the keyboard.

Finishing the example

Line 2

Line 3

Line 4

Line 5 (note we zoomed in to work in the smaller area)

Line 6 (we zoomed in further on the left image - zooms do not have to match)

Line 7