Interpolate Layer (PSE 15+)

Sometimes, you may want to alter the behavior of an animated object or to add a new object into an existing frame sequence.

0. Decide on the initial and final frames of the planned event.

For example, let's make the creeping line appear in the Frame 9 and disappear in the Frame 21 (screenshot).

1. Select the "initial" frame and then set the "object" layer's position (fig. 1) and/or opacity.

2. Select the "final" frame and set the layer position (fig. 2) and/or opacity.

3. In the "Frames" list, select the "initial through final" frame range (fig. 3).

4. Make sure the "object" layer (or multiple layers) is selected in the "Layers" list (fig. 4).

5. Run "Interpolate Layer" command (fig. 5).

The script automatically re-calculates the layer position and opacity for the intermediate frames.

A video-tutorial on this topic is available here.