CAP 151 -
Introduction to Computer Animation
Lesson 3 - Layer Control
This lesson discusses trimming layers and using more effects. Objectives important to
- Working with layers
- Moving and trimming layers
- Slip editing
- Sequence layers
- Looping footage
- Time stretch
We will not hit all the tutorials in this lesson. The most important ones are listed above.
Tutorial Notes and Questions
Work through the exercises and turn in your answers to all questions below as part of the homework for this assignment.
Tutorial 1 (Working with Layers):
- Start After Effects. Load the project for this lesson. Open the 01-Layer Practice*starter comp.
- Note the current order of the layers in this comp. Preview it.
The text offers a useful phrase: open air. This means time frames on the timeline that occur before and/or after a short layer runs in the current comp. A layer that does not run for the length of the comp will have open air.
Notice that the layers in this comp also overlap in time.
- Change the order of the layers as instructed. Preview it again.
The text is not clear on this simple concept: layers play based on where they are in the timeline, not where they are in the the stack of layers. Their play order has nothing to do with their stack order. The stack order does have one effect: it controls which layers appear in front of other layers. You should notice this effect in this exercise.
- New material: we do not have to play an entire layer. The layer may have internal in and out points, like the ones in this comp. This means that they have internal markers, which we place in After Effects, to show at what internal points they start and stop. The layer also has external in and out points, which are the ones we have seen already. They control when the layer plays in the comp.The internal markers are visible on the current layers as color transitions inside the length of each layer's bar. The layer does not play in time frames where it is grayed out. (The text calls the grayed out area "ghosted".)
At the bottom of the timeline, note the button with the left and right curly braces. (Your text calls them a "pair of brackets".) Clicking this button displays several information columns for the layers. The tutorial wants us to work with the In, Out, and Duration columns. Hide the Stretch column for now.
- Practice dragging the layer in time as instructed. You will be changing the comp in and out points of the layer. Note the changes in the columns displayed in the step above.
Note the shortcut to set the time
at which a layer starts in the comp, using the left square bracket key, and the shortcut to set the time a layer ends with the right square bracket key.
Question 1: Why would it be unlikely that you would use both the shortcuts above on the same layer?
- If a layer needs to be trimmed, and you have not done so, use the procedure in this step.
Drag the end of the layer, not the bar itself. This works with either end of the layer. Note that this changes the In or Out values (depending on what you are dragging) as well as the Duration value. The text points out that you can still see the portion of the layer that you have chosen not to play as a "ghosted" protion of the bar. The process is called trimming in place.
- This step is an alternative to the method in step 6, since it does the same thing. Trim a layer in place by clicking the point on the timeline when you want the layer to start, and pressing Alt-[. This trims the in point of the layer.
Question 2: What is the quick method (from this step) to trim the out point of a layer?
- The text continues to introduce the Slip Edit tool. This lets us change the part of the layer that plays (its internal in and out)
To see the Slip Edit tool, hover over a ghost section of a layer. As described in the text, the tool looks like an arrow with a head on each end, each arrowhead blocked by a vertical line.
Dragging this tool changes the internal in and out points of the layer, but it leaves the external in and out points alone.
- If you can't see the ghost areas, you can produce the Slip Edit tool by turning on the Pan Behind tool and hovering over the layer bar.
Question 3: What are the hot keys to toggle the Pan Behind tool and the Selection tool?
- Open the indicated comp to see features related to keyframes in layers. Select all layers and display Opacity as instructed.
The text reveals that keyframes are attached to the layer they appear in, not the comp itself. Not surprisingly, when you move a layer, its keyframes move as well.
To move a layer without changing the timing of its keyframes, use the Slip Edit tool.
Do the sub-step about moving selected keyframes with the Slip Edit tool. As you might expect, if you selected keyframes and move the
layer, the selected keyframes move too, but the unselected ones do not.
The next section of the lesson takes us to the Graph Editor, and introduces several useful commands.
Tutorial 2 (Sequence Layers):
- Open the indicated comp. Four layers are at the start of the comp.
- You will use an automated process by selecting all layers, then selecting Animation, Keyframe Assistant, Sequence Layers. This will place the the layers in time sequence, based on their order in the stack. (So the stack order can have an effect on the timeline, it just won't do it without our telling it to do it.)
Undo the sequencing before you do the next step.
- In this step, turn on Opacity. Follow the instructions to select a layer, use the Sequence Layers command again, and turn on the Overlap feature. Use the default values as instructed, including Dissolve Front Layer. Preview to see the effect of the crossfade from the first layer to the second.
- Step 4 shows what happens if you choose Cross Dissolve Front and Back Layers.
Question 4: Describe the difference between the two effects. (Actually describe them. Saying one looks bad in not a good answer.)
- Open the indicated comp to explore using the Cross Dissolve option.
Question 5: After trying out step 5, describe why you prefer one option over the other for this comp.
- Step 6 opens a new comp to do a sort of slide show between its images.
The first trick is to select all four layers, from the bottom up. (Never made a difference in any other program, did it?) The reason is seen at the bottom of page 68: the layers will eventually be shown in bottom to top order.
Set all layers to start at the same time, the start of the comp. (For now.)
The next step of the plan is revealed. (Personally, I would have words with someone who did not tell me what they wanted before I started work on the comp.) We want each picture to be shown for 4 seconds, and to crossfade for 1. This is why you set the out markers for all four layers at 4;29 (4 seconds and 29 frames).
Right-click a layer and use Sequence Layers again, setting Overlap to 1 second of crossfade.
Question 6: The text asks which crossfade type you should choose. Which did it recommend already?
Turn on the Opacity keyframes and preview the comp.
Tutorial 3 (Looping Footage):
- Open the file indicated for this tutorial.
- Import the indicated file into your My Sources folder.
Play the movie to confirm that it begins the same way it ends, which makes it a candidate for looping.
- Having added the movie to the your folder, add it to the open comp as instructed. Note that the movie is a third as long as the comp.
Select the movie again in the Project panel.
Find the Interpret Footage button in the bottom left corner of the Project panel and click it. (It it illustrated on page 69.) Change the loop value to 3 and click OK.
- The layer now has a ghost portion. This indicates it is not really going to play for 30 seconds yet.
Select the layer in the timeline, press End to go to the end of the comp, then press Alt-] to move the out point of the layer to that frame. Preview the comp.
Practice with other movies as instructed on page 69.
Tutorial 4 (Image Sequences):
- The next tutorial shows us alternative ways to do more things we know how to do, and offers some new features as well.
This time we start by setting a parameter for the program itself.
Text difference: There is no Preferences menu in the Windows version of the program.
Open the Edit menu, select Preferences, and select Import. As the text explains, you will import a sequence of TIFF images for this tutorial. Images of this sort have no frame rate of their own, so set the frame rate for Sequence Footage to 29.97, which will match the rate we are using for comps.
In the project panel select your My Sources folder, and press ctrl-i to import files to it.
Navigate to the specified folder and find 10 TIFF files containing pictures taken by Eadweard Muybridge. Select the first one, and click the TIFF sequence checkbox. Click Open.
- You will have imported all ten files with the same base filename as one footage item. The text misleads us bit next, but let's go along with it.
The sequence is only 10 frames, which will play and be over before viewers notice. The text says to set it to loop 100 times. This is awfully long, but it will never happen. Stay close.
- We still don't have a comp for this footage. Create one by dragging the image sequence object and dropping it on the Create a New Composition button, shown on the right. As the text explains, the new comp will take its settings from the item dropped on the button.
Press Ctrl-K to open the comp's settings and change the duration as instructed. The comp is also created in the wrong folder, so move it as instructed.
- Guess what? Playing a 10 frame sequence at 29.97 fps still plays it too fast, no matter how many times you play it. (Well, Muybridge was only taking photos, not a movie.)
Go back to the Interpret Footage dialog for the TIFF sequence again. This time, find the Frame Rate field, and change it. The text suggests starting with 10, previewing the comp, and changing the Frame Rate as needed to make a good movie. Note that this frame rate overrides the rate you set in step 1. So what did you set it for? The next set of TIFFs you get might actually be intended to be a movie.
- Step 5 leads into the last objective for the lesson: Time Stretch.
To see the effect of time stretching, follow the directions in step 5 on page 71. However, preview before and after applying the time stretch to understand the difference. The point here is that applying a time stretch affects the keyframes that are in the layer. Interpret footage does not have this effect.
Assignment 5: To be announced.