Week 11

Week 11 – Topics

Track & Key
Tackling several essential skills for creating special effects
Resources for source files

  • creating track points
  • important Tracker options
  • applying stabilization
  • compensating for stabilized footage
  • fixing bad tracks
  • tracking interlaced footage
  • motion tracking
  • applying a motion track
  • Radio Waves effect
  • applying tracks to effect points
  • perspective corner pin tracking
  • Bezier Warp effect
  • stabilizing Position, Rotation, and Scale
  • interpolating obscured tracks
  • working with high-definition footage
  • keying using the Keylight effect
  • improving keyed composites
  • creating garbage mattes
Week 11 – Assignments

1) If you have access to a video camera, shoot your own footage of people walking across campus or down the street. Then practice tracking them and placing text or other objects over their heads and the like. (If you don’t have access to a camera, try to find stock footage to complete the exercise or use footage from our textbook DVD.)

2) Take a handheld camera and shoot footage of objects with four clear corners – such as a poster, sign, painting on a wall, or a license plate or billboard on a bus going by. Use the Perspective Corner Pin track skills you learned in 04-Corner Pin to replace it with your own source. (If you don’t have access to a camera, try to find stock footage to complete the exercise or use footage from our textbook DVD.)

3) Optional: For those of you who are interested in learning more about keying, complete the exercises outlined in our textbook on pages 234-240. This part is not required for your homework, but for those of you who are interested, this is a good exercise to complete.

4) Continue work on your final project. Start working on your storyboard if you haven’t done so already. Storyboards are due next week (Week 12).  Start working on your illustrations, video and photos — or start finding your assets through the resources listed on the Resources page. You should get started on creating your project in After Effects BEFORE Week 14.

Genres – Motion Graphics
Collage

Also know as “Kitchen Sink” style, collage my involve throwing in everything to the kitchen sink. Just like the collages of cut out magazine images we make in second grade, this style has the same feel, an often frenetic, rapid animation style. Stardust does this well.

Film

this style is seen in film titles and trailers. There is a pacing common to trailer graphics and they have a heavy focus on typography. Picture Mill does good stuff here.

 

Lesson 9: Track & Key

Topics covered:

  • 222 creating track points
  • 223 important Tracker options
  • 224 applying stabilization
  • 225 compensating for stabilized footage
  • 225 fixing bad tracks
  • 225 tracking interlaced footage
  • 226 motion tracking
  • 227 applying a motion track
  • 228 Radio Waves effect
  • 230 applying tracks to effect points
  • 231 perspective corner pin tracking
  • 233 Bezier Warp effect
  • 234 stabilizing Position, Rotation, and Scale
  • 236 interpolating obscured tracks
  • 237 working with high-definition footage
  • 238 keying using the Keylight effect
  • 239 improving keyed composites
  • 240 creating garbage mattes
Page  222 creating track points

Basic Stabilization
We’ll start with one of the easiest but most useful tasks: stabilizing footage where the camera wasn’t entirely steady.

1.  Open this lesson’s project file: Lesson_09.aep. In the Project panel, the Comps folder should be twirled open (if not, do so now). In this folder, locate and double-click 01-Stabilization*starter to open it.

2.  This comp contains one layer: Wildebeests.mov. Press “0” on the numeric keypad to RAM Preview the clip and watch it closely: The image bobs up and down slightly. If this movement isn’t obvious, place your cursor near the ground; you will see the ground shift as the clip plays. While previewing the footage, look for items that might make good features to base your stabilization off of: something that has good contrast, that keeps roughly the same shape and position throughout the shot, and that isn’t obscured by another object.

3.  In the upper right corner of the application window, click on the Workspace popup and select Motion Tracking. This will open the Tracker panel. Note that it currently says Motion Source is set to None.

Tracking and stabilization need to take place in the Layer panel so you can focus on just that clip. Double-click Wildebeests.mov to open its Layer panel; you will notice in the tracker panel that Motion Source automatically changes to this layer’s name.

Track Points
4.  Click the Stabilize Motion button in the Tracker panel. This will create a track point, which consists of two boxes and a crosshair:

  • The inner box is the feature region, which you will use to enclose the feature you wish to follow.
  • The outer box is the search region, which tells After Effects how far to search in the next frame for a group of pixels that matches what was in the feature region in the previous frame.
  • The crosshair in the middle of these boxes is the attach point. It is the center for any stabilization that takes place. When tracking, it defines where the Anchor Point for the new layer will be placed.

5.  You need to set up your track point at the time you plan to start the track, so press H to return to 00:00. Hover over the track point until the cursor changes to a black pointer with four arrows at its tail, which indicates you can move the entire track point together as a unit. Drag the track point to a feature you identified in step 2. The bright cloud fragments make good candidates; we’re going to pick the one on the left. Center the track point over your desired feature. While you’re dragging, you’ll notice that the track point turns into a magnifier, making this easier.

6.  The feature we chose to track is larger than the default size of the feature region. Drag out the feature region’s corners until it is just big enough to enclose the entire cloud fragment, including a little fringe around it. Also make sure the search region is bigger than the feature region, taking into account how much the feature moves from frame to frame. Zoom into the Comp panel if you need to.

Page  223 important Tracker options

Performing the Track
7.  In the Tracker, click on Options. To not waste time on a bogus track, you should always verify these are set correctly before performing any track:

  • The most important section is Channel. Set this based on how your feature stands out from the pixels around it. In this case, the clouds are all the same basic hue, but the bright bits have considerably different luminance than their surroundings – so check Luminance.
  • You can usually leave Process Before Match disabled; use it only if you have trouble tracking. If the footage is out of focus, enable it and try Enhance; if it is noisy, try Blur.
  • You always want to leave Subpixel Positioning on, and most of the time you want to leave Track Fields off (see the sidebar When Tracks Go Wrong). We usually leave Adapt Feature On Every Frame off; enable this switch if your feature constantly changes shape or size every frame. We often set the popup below to Adapt Feature and leave Confidence at 80% – this tells After Effects to keep looking for the same feature unless it thinks it has changed too much. Click OK when you’re done.

8.  Click on the Analyze Forward button in the Tracker. After Effects will search each frame for the feature you’ve defined. When it is finished, you will see a motion path created for Track Point 1. In this case, its individual points will be all bunched together, as the feature doesn’t move that much. Press “U”, and in the Timeline panel you will see a large number of keyframes applied to Track Point 1. It’s a good idea to save your project after performing a successful track so that you can revert back to it if something goes wrong afterward. After that, the next step is taking these keyframes and doing something useful with them!

Page  224 applying stabilization

Applying Stabilization
9.  In the Tracker, make sure Track Type is set to Stabilize and Motion Target is set to Wildebeests.mov (if it isn’t, click on Edit Target). Then click Apply. A Motion Tracker Apply Options dialog will open; leave it at its default of X and Y Dimensions and click OK. After Effects will bring the Comp panel forward; press Shift + A to reveal the new Anchor Point keyframes in the Timeline panel. These keyframes offset the movement detected for your feature region, causing the footage to be stabilized. To verify that your stabilization worked, RAM Preview. You might want to place your cursor over a feature in the Comp viewer to verify that the footage is no longer bobbing as much as before. It may still wander very slightly; it is hard to get a perfect track – especially on your first try! Congratulations: You now have the basic skills required to perform most motion tracking and stabilization chores.

Cleaning Up
Now for the bad news: Scrub the current time indicator along the timeline and watch the top edge of the Comp viewer. That pink area you see is the comp’s background color peeking through (we made it an obnoxious color to make it more noticeable). As a result of the layer being moved to make it appear stable, it is no longer centered, and therefore doesn’t cover the entire frame. Let’s try a few ways to compensate for this. The best solution will vary from job to job, depending on how much the layer moves and what looks best.

10.  Select Wildebeests.mov and press “S” to reveal its Scale. Scale up the footage slightly until it covers the entire frame throughout the entire timeline. The cost of this is a slight softening of the image as you scale over 100%.

Page  225 compensating for stabilized footage

11.  Return the layer’s Scale to 100%, and press F (the apostrophe key) to reveal the Action and Title Safe grids. If the offending area is well outside the Action Safe area, you may be able to rely on the television’s bezel cutting it off. However, you should fill these areas with something, just in case. Here are a couple of ideas:

  • Cover the background with a solid. Select Layer > New > Solid. Click on the Make Comp Size button, and eyedropper a color from around the edges of the footage. Click OK and drag this new solid down the layer stack to sit behind your tracked footage. You will now have a solid color border to fill in the revealed areas.
  • Select Wildebeests.mov and type Cdon Mac (Ldon Windows) to duplicate it. Select the copy on the bottom (layer 2), press H, then press ato reveal its Anchor Point; its value should read 360,243 (its initial location at the center of the comp). Click on Anchor Point’s stopwatch to delete the keyframes created by applying the stabilization. You will now have an echo of the footage in the revealed areas. This is the approach we took in our version, Comps_Finished > 01-Stabilization_final.
Page  226 motion tracking

Basic Tracking
Now that you know your way around the Tracker, let’s put your newfound skills to work with a typical motion tracking exercise.
1.  Close all previous comps by selecting Close All from the Comp panel’s dropdown menu. In the Project panel, double-click Comps > 02-Tracking Objects*starter to open it. It contains three layers: the wildebeest footage from the previous exercise, a text layer, and a small pointer. The plan is to make the text and pointer follow the head of one of the wildebeests, as if we could read its thoughts.

2.  After making sure the Tracker panel is visible, press H. Select the Wildebeests.mov layer, then click Track Motion in the Tracker. This will open your clip in its Layer panel and create a track point. Click inside the track point somewhere that you see the black cursor with the four-arrow tail, and drag the track point until it is centered over the horns of the wildebeest at the left. As it so happens, the default size of the feature region nicely fits the horns, so there’s no need to resize these boxes.

3.  Click on the Options button in the Tracker and position the Motion Tracker Options dialog where you can still see the wildebeest. First is setting Channel. What sort of contrast is there between the wildebeest’s horns and the sky behind? Luminance – so select that option. Next comes the Adapt Feature settings. The feature you want to track – the horns – changes over the course of the shot as the wildebeest turns his head back and forth. In this case, enable the Adapt Feature on Every Frame option. Set the popup below to Stop Tracking so it will be obvious if After Effects can’t follow this feature any longer. Then click OK. Click the Analyze Forward button in the Tracker. After it is finished, After Effects will display the motion path for the track in the Layer panel.

Page  227 applying a motion track

Applying the Track
Time to apply the results of your motion tracking. There’s a quick and dirty way to do this, and a more clever way…
4.  To decide which layer will receive your motion track, click the Edit Target button in the Tracker panel. In the Motion Target dialog that opens, there will be a popup for Layer. Hmm…two layers want to get the track, and you can select only one. You could apply the track twice, or you could use a trick you picked up back in Lesson 6: using parenting and null objects.

5.  Click Cancel in the Motion Target dialog. Instead, create a dummy layer to receive the track to which you can later attach as many other layers as you want. Select Layer > New > Null Object; it will appear in the Timeline panel. Back in the Tracker panel, click on Edit Target again, and this time select your null. Click OK and verify that the name of the null appears next to Motion Target. Click on Apply and click OK in the Motion Tracker Apply Options dialog that appears. The Comp panel will come forward. Select your null object, and you will see its new motion path in the Comp panel. Deselect all and clean up the display. Scrub the current time indicator and note how the upper left corner of the null follows the head of the wildebeest.
6.  Time to parent your other layers to this null:

  • Select the text layer I have no idea where, then S+click the “pointer” layer to select it as well. Drag them into your desired position in relation to the second wildebeest’s head.
  • Reveal the Parent panel (if it’s not already visible). With your two layers still selected, click on the Parent popup for either one of them and choose your null. (You can turn off the eyeball for the null; it will still work as a parent.) RAM Preview: The text and pointer will follow the wildebeest across the comp. Our version is in Comps_Finished > 02-Tracking Objects_final – we added a second line of text to make the shot more interesting. And don’t forget to save your project…
Page  228 Radio Waves effect

Tracking for Effects
In addition to making a layer follow an object in another layer, you can also use motion tracking to have effects follow a feature around a layer by assigning the tracked motion to an effect point. In this exercise, you will track a mountain peak and use results to send out radio waves from that peak.

1.  In the Project panel, double-click Comps > 03-Effect Track*starter to open it. It contains one layer, which is an aerial pullback over a range of mountain peaks. RAM Preview it, thinking about which peaks might be candidates for tracking.

2.  Select Mountain Peaks 2.mov. Then apply Effect > Generate > Radio Waves. (If needed, dock the Effect Controls panel into the Project frame.) RAM Preview. The mountain footage will be replaced by a series of concentric blue circles emanating from the center. Press Nfor now, so you can see several waves on screen and become familiar with the Radio Waves controls:

  • In the Effect Controls panel, make sure the Wave Motion section is twirled down, and increase Frequency to increase the number of waves. Alternatively, you can reduce the Expansion value to slow down how fast the waves fly off screen. Then try decreasing the Lifespan: You will notice that the waves start to die away as they get older.
  • If needed, open the Stroke section. Decrease the Start Width and increase the End Width; you will now see the waves start skinny and grow thicker with age.
  • Press H, go to 00:00 and click on the stopwatch next to Producer Point (near the top of the Effect Controls) to enable keyframing. Move the time indicator a few seconds later, click on the crosshair icon next to Producer Point, then click somewhere in the Comp viewer. Do this a couple more times until you reach the end of the comp. RAM Preview: You will notice that the waves remember where they were born, creating an interesting trail over time.

3.  Make sure the Tracker panel is visible; if not, select the Motion Tracking Workspace or open Window > Tracker. Make sure Mountain Peaks 2.mov is still selected, then click Track Motion in the Tracker panel. The Layer panel will open. The original footage should now be visible again, even though the Radio Waves effect is still applied. This is controlled by the View popup along the bottom of the Layer panel: Switch it to Radio Waves (the motion path for Producer Point will be visible), then back to Motion Tracker Points.

4.  Press H to make sure you are at the start of the clip. Hover the cursor over the track point until the now-familiar black pointer with the four-arrow tail appears. Click and drag the track point over one of the peaks. We chose the pointy peak near the middle of the frame, as it remains visible for the entire shot and keeps good contrast with its background during the shot. Be sure to enlarge the track and search regions to enclose a good part of the peak.

5.  Click on Options in the Tracker. The foreground peaks are about the same brightness as the mountains behind but are a different color; therefore, set Channel to RGB. The mountain peaks only change shape a little during the shot, so go ahead and disable Adapt Feature on Every Frame, and instead set the popup below to Adapt Feature (meaning it will adjust its search only when the feature has changed quite a bit). Finally, give your track point a name at the top of the dialog, such as “middle peak.” Click OK.

Page 230   applying tracks to effect points

6.  Click Analyze Forward in the Tracker. If the track stops before the end of the clip, press Analyze Forward again – this will refresh and continue the track. When finished, click Edit Target to open the Motion Target dialog. Make sure that Effect Point Control option is selected, and that Radio Waves/ Producer Point is selected in the adjacent popup. Click OK. Back in the Tracker click Apply, then OK when the Motion Tracker Apply Options dialog appears. This will replace your trial animation in step 2 with the motion tracker’s data.

7.  RAM Preview, and Radio Waves will create a nice set of moving circles for you. But where are the mountains? Radio Waves does not have any “composite” options that allow you to see it and the underlying layer. No problem – just duplicate the layer and use that:

  • Twirl up the open parameters in the Timeline panel to reduce the clutter. Select Mountain Peaks 2.mov and use Edit > Duplicate.
  • Select the bottom copy of Mountain Peaks 2.mov and select Effect > Remove All. Tweak the Radio Waves effect on the top layer to taste. Reveal the Modes column and try compositing the waves with modes such as Add or Overlay. Our version is saved in Comps_Finished > 03-Effect Track_final. Make sure you save your project. In an Idea Corner at the end of this lesson, we’ll also challenge you to continue working with this composition and track a second peak, applying the results to an effect with two effect points. Applying tracks to effect points is a skill that is useful in both motion graphics and visual effects. For example, you can apply the track to the center of a radial blur effect to create an interesting selective focus look. It is also quite common to track light sources in real scenes or 3D renders and apply them to lens flare centers. Next, you’ll move up to a more challenging task that requires tracking four effect points.
Page 231   perspective corner pin tracking

Corner Pin Tracking
One of the greatest uses of motion tracking is to replace one object with another. For a replacement to be convincing, not only must it be in the correct position; it must also exhibit the same perspective as the original. This is where corner pin tracking comes in. With this method, you typically track the four corners of a rectangular shape and distort your new layer so that its corners match the original object’s corners. It’s like motion tracking, times four – and more… Four Track Points

1.  In the Project panel, double-click Comps > 04-Corner Pin*starter to open it. RAM Preview it, paying particular attention to the computer monitor. Your task in this exercise will be to replace its display.

2.  In the Project panel, twirl down the Sources folder. Select Heart Monitor.mov and add it to your composition. Initially, it covers the entire frame; After Effects will shrink it down once you’ve completed the track.

3.  Press H to return to 00:00. Make sure the Tracker panel is open (if it isn’t, select the Motion Tracking workspace). Click on the Motion Source popup and select MRI Computer.mov. This will open its Layer panel, but no track points will be visible yet. Click Track Motion: One track point will appear in the Layer panel. Then click on the Track Type popup and select Perspective Corner Pin. Now you will see four track points in the Layer panel – one for each corner

4.  Hover the cursor over Track Point 1 until you see the black cursor with the four-pointed arrow at its tail. Drag this track point over the upper left corner of the computer monitor. The contrast between the blue of the old display screen and the black around it makes it a great feature to track. The feature region is a bit larger than necessary to enclose this feature; to help increase the accuracy and speed of the track, reduce the size of this region. Zooming into the Layer panel display will make both sizing and placing it easier.

The Attach Point
5.  After you have positioned the feature region, you need to pay extra attention to the attach point: the + symbol that defaults to the center of the feature region. The attach point is where a corner of your new layer will be placed. If the attach point was placed inside the glowing area of the old display, this fringe would peek out from behind your new layer. Therefore, make sure the attach point is just beyond the bright blue area. Zoom further into the Layer panel to make it easier to move this point.

6. Repeat steps 4 and 5 for the remaining three track points. Then press S/ to recenter the viewer and return to normal magnification.

7.  Click on the Options button. Our features have strong contrast, so select Luminance under Channel. The other settings used earlier (Adapt Feature On Every Frame = off; the popup below set to Adapt Feature) are fine. Click OK. Click Analyze Forward. If you’ve made your feature and search regions reasonably small, the track should proceed very quickly even though there are four points to track.

Applying and Improving

8.  Make sure Motion Target is set to Heart Monitor.mov; if it isn’t, click on Edit Target and set it. Then click Apply. Take a moment to examine the layers in the Timeline panel:

  • MRI Computer.mov has a set of keyframes for each of its four Track Points.
  • Heart Monitor.mov has had the Corner Pin effect applied, with a set of keyframes for each of its corners.
  • Heart Monitor.mov also has a set of Position keyframes, which reflect how the center of the new display moves to match the movements in the computer monitor. After applying a corner pin track, both layers might be selected; bring the Timeline panel forward and press @to deselect all. RAM Preview; the new display will now track the computer monitor. However, there is still some blue peeking out around the corners of the display, even though you were careful in how you placed the attach points. You are seeing the results of the monitor’s CRT being bowed out (it is from before the era of flat-panel displays). Therefore, this composite will require a little more work to make the result convincing:
Page 233   Bezier Warp effect

9.  Select Heart Monitor.mov and choose Effect > Distort > Bezier Warp. This effect allows you to use the familiar Bezier handles (from mask shapes and motion paths) to gently warp a layer. Look at the Comp panel: After applying this effect, your new screen went flying off into space! This was caused by the order in which the effects are being applied. In the Effect Controls panel, drag Corner Pin to below Bezier Warp; now things will look normal.

10.  Bezier Warp needs to be edited in the Layer panel. However, you need to watch the results in the Comp panel while working. Double-click Heart Monitor.mov to open its Layer panel. Then either undock this panel or otherwise arrange it so that you can see it and the Comp panel at the same time. In the Layer panel, set the View popup to Bezier Warp. You will notice a series of 12 crosshairs around its outline. Leave the ones in the corners – the warp vertices – alone. Slowly drag the handles (“tangents”) along the left outward, watching the result in the Comp panel. Move them just enough until the blue fringe has been covered up in the final composite. Do the same for the handles along the bottom. The handles along the top don’t need adjusting; if anything, the handles on the right may need to be pulled in slightly to compensate for the perspective and bow of the computer monitor.

When you’re happy with the warp, re-dock the Layer panel, bring the Comp panel forward, and RAM Preview. Congratulations – you just finished a fairly challenging track assignment! (Save your project…) Our version is Comps_Finished > 04-Corner Pin_final; we added the “filmic glow” trick you learned back in Lesson 3 to spiff up the final composite and better blend the results.

Page 234   stabilizing Position, Rotation, and Scale

Background Replacement
In this final exercise, you will take a handheld shot of a pair of actors on a greenscreen stage, stabilize the shot, remove (“key out”) the green, and place the result over a new background to make it appear the shot originally took place outdoors. For an added challenge, this composition is created at the high-definition resolution of 1920°—1080 pixels. Note that we have saved this source footage using the common HDV frame size of 1440°—1080 pixels. These pixels are “anamorphic” in that they are supposed to be displayed wider than that, yielding the same result as a normal HD 1920°—1080 frame. It will look normal in the Comp panel; in the Layer or Footage panels, you will see the original, squeezed image. Read the Tech Corner later in this lesson for more on high-def issues.

Stabilizing Position, Rotation, and Scale
This will be your most challenging track in this lesson, as you will need to stabilize not just position but also rotation and scale. The good news is the greenscreen stage already has nice tracking dots placed on it. The bad news is one of the actors walks in front of the dots you need…

1.  Close your previous comps. In the Project panel, double-click Comps > 05-Keying*starter to open it. If you can, arrange your panels so you can view the Comp panel at 50% Magnification and Half Resolution; if not, set Magnification to 33% and Resolution to Third. RAM Preview this shot, paying particular attention to the tracking dots. Any dots that go off screen during the shot are of less use. Note that the camera moves in closer during the shot and rotates a bit. The new background you will be placing this action over does not move. Therefore, you will need to stabilize position, rotation, and scale!

2.  Select PXC_Europa.mov and press H. Make sure Window > Tracker is visible and click Stabilize Motion. The movie will open in the Layer panel with a default track point. In the Tracker panel, enable the checkboxes for Rotation and Scale in addition to the default Position. This will create a second track point. In order to stabilize rotation and scale, After Effects needs to measure distance between two points over time, as well as the angle between them.

3.  Still at 00:00, start with Track Point 1 on the left. Drag Track Point 1 over the upper left tracking dot, because it remains visible throughout the entire shot. Drag a corner of its feature region (the inner box) to make it just larger than the green square on the background. In the process, bump the search region (the outer box) to be about twice the size of the feature region.

For Track Point 2, think for a moment about which dot to track. It should be as far away from Track Point 1 as possible: The greater the distance between track points, the more accurate the scale and rotation tracks. It would hopefully remain visible throughout the shot as well. The second actor walks in front of all of the dots on the right; the middle dot in the upper row is obscured the least – so place Track Point 2 over it. Resize Track Point 2. Again, do not make the track point larger than necessary; if you do, it will slow down the track, and After Effects will have more trouble when the actor walks in front of the dot.

4.  In the Tracker panel, click on Options. The dots are the same color as the background but lighter, so pick Luminance for Channel. Further down, Adapt Feature On Every Frame should be off. Click on the popup under – neath; since we know one of the features we will be tracking will be obscured during part of the track, select the option to Extrapolate Motion. This tells After Effects that if it cannot find the feature it’s tracking, keep going in the same direction and hope it reappears. Click OK.

5.  Time for some trial and error. Click Analyze Forward and keep your eye on Track Point 2, especially when the actor walks in front of its dot:

  • If you set up a good track point, it will wander temporarily when the actor walks in front, but will find its dot again a few frames after he passes.
  • If the track point follows or appears to “bounce off” the actor when he passes in front of the dot, the track point was too large. First Undo to remove the old track, tighten up the feature region, and analyze again.
  • If the track point finds the dot after the actor passes but then loses the dot again later, the search region is too small. Undo, increase the outer rectangle very slightly, and try again. If you tried several times and still can’t get a good track, open Comps > 05-Keying*starter2 and continue with this comp instead. Double-click layer 1 to open its Layer panel and set View to Motion Tracker Points.
Page 236  interpolating obscured tracks

6.  With PXC_Europa.mov selected, type uto see all of the tracker’s keyframes. There will be a noticeable gap in Track Point 2’s Attach Point keyframes when the actor passed in front of the dot. Let’s make sure After Effects interpolated the motion correctly through that area. Slowly scrub the current time indicator in the Timeline panel while watching the Layer panel. When the actor’s chin crosses into Track Point 2 at 01:11, you will see it snap away from the dot it was tracking. Stop at this frame, and delete the corresponding Attach Point keyframe. Scrub later in time until you see Track Point 2 snap back into its correct position over the dot – that’s a good keyframe. Delete any keyframes between this one and the keyframe you deleted above (there’s probably just one, in the middle of the gap). Now as you scrub through this area, Track Point 2’s boxes will still wander, but the attach point (at the end of the line connecting Track Point 1 and 2) will stay on course. Save your project.

7.  Whew! That was a lot of work. Now for the payoff and some final tweaks before moving onto the greenscreen:

  • Make sure Motion Target is still set to PXC_Europa.mov and click Apply, then OK. After Effects will bring the Comp panel forward.
  • RAM Preview; the actors will now be stable. However, their layer will get smaller as After Effects compensates for the camera movement, leaving a gap at the bottom of the composition. Press N, where the gap is at its largest.
  • Press @to Deselect All and twirl up the Motion Trackers section in the Timeline panel to save space. Still at time 03:23, disable keyframing for Position, then reposition PXC_Europa.mov to where it just sits on the bottom of the composition (around Y = 482). Your next task is to “key out” the green in the PXC_Europa.mov layer so you can see a new background layer behind it. The term keying is short for keyhole: creating a cutout so you can see through one object to view another.
Page 237   working with high-definition footage

In the final exercise in this lesson, you are working with high-definition (HD) footage. An HD frame can contain up to six times as many pixels as a DV frame, so you will need a lot of RAM, a fast computer, and hopefully a large monitor. Even then, you’ll need a few tricks to make things manageable. Work Smarter, Not Harder In most lessons in this book, you’ve been working at Full Resolution and up to 100% Magnification so that you could see every pixel of your result. This would be terribly slow with HD. Therefore, it is quite common to work in a composition at 50% Magnification and Half Resolution. This is the way we’ve set up the comps in this exercise. If you have a small screen or a slow computer, you may need to go smaller than this (such as 33.3% Magnification and Third Resolution). On a real job, you would always go back to 100% Magnification and Full Resolution for a final confidence check; always render your final at this size as well. Additionally, this shot touches on two additional technical issues that you will often have to deal with when working in HD: non-square pixels and 3:2 pulldown. Pixel Aspect Ratio True HD comes in two frame sizes: 1920×1080 pixels (“1080”), and 1280×720 pixels (“720”). This is a lot of pixels to record to videotape. Therefore, some HD video formats – such as HDV and DVCPRO HD – use fewer pixels and expect software or hardware to stretch the final images back out to full size later. One of the most common formats is the “1080” flavor of HDV. On tape, this frame actually contains only 1440×1080 pixels.

As a result, the pixels are not square, and unprocessed footage would look skinny on a computer monitor. To compensate for this, After Effects needs to know its pixel aspect ratio so that it can perform the required stretch for you. This is set in the Interpret Footage dialog for each clip. We’ve already set this popup correctly for you; always check it for any HD footage you receive. (Note: Since we cannot be sure that you have a compatible HDV codec installed on your computer, we saved this file using a more commonly available QuickTime codec.)

3:2 Pulldown
Video in North America is normally shot at 29.97 fps. By contrast, most film is shot at 24 fps. Some people want their video to look more like film. To accommodate this, some video cameras can shoot at “24” fps. However, many still need to record a tape at 29.97 fps.

To make the math work, they first capture images at the almost-24 rate of 23.976 fps. They then spread one frame across three video fields (remember, there are two fields in each video frame), then the next source frame across two fields. This process is known as 3:2 Pulldown; the result has an effective frame rate of 29.97 fps. If you need to work with video that has 3:2 pulldown, you can remove the pulldown to get back to the originally captured frames. This results in fewer, cleaner frames to process. If you need to remove pulldown on HD footage, open the Interpret Footage dialog, set Separate Fields to Upper, then click on Guess 3:2 Pulldown. (We have saved this exercise’s clip at its original, non-pulldown rate of 23.976 fps.) 3:2 Pulldown is covered in more detail in the Appendix.

Page 238   keying using the Keylight effect

Keylight
Continue to use the comp you built in the prior section, or start with our version 05-Keying*starter3. 8 Select the layer PXC_Europa.mov, press Hand apply Effect > Keying > Keylight. This is a high-end keying plug-in that comes bundled with After Effects CS4. Then follow these steps to perfect your key. This is an interactive process, so have patience and be prepared to repeat some of these steps to balance the desired results:

  • In the Effect Controls panel, click on the eyedropper for Screen Colour and click in a green area near the actor. This is your initial key. Not bad! However, if you look at the right side of the actor’s neck, it’s partially transparent and the background layer is showing through. For now, turn off layer 2 so you can concentrate on your key. If not already enabled, toggle on the Transparency Grid to better check the transparency of your key.
  • Back in the Effect Controls panel, change the View popup to Status. This produces an exaggerated display of the key’s transparency.
  • Twirl down the Screen Matte section. Slowly increase Clip Black until most of the gray outside the actor disappears. Press C(L) to scrub in finer increments. You may leave the gray squares in the background (otherwise you’ll start cutting into his head).
  • Slowly increase Screen Gain until the rest of the gray just disappears. Balance these two values against each other until you’ve made the smallest total increase while eliminating the gray.
  • Slowly decrease Clip White until the gray in the actor’s head turns white or light green. Don’t push this too far; you want to keep some gray (which denotes transparency) around his hair’s edge, as well as in the motion blurred areas as he moves.
  • Scrub the current time indicator through the timeline, checking that the black areas stay black and the light areas stay light.
  • Change Keylight’s View back to Final Result and preview your work. If the edges around the actors are too hard-edged, increase Clip White slightly.
Page 239   improving keyed composites

9.  Turn on the Video switch for layer 2 again so you can see your key in the context of its new background. Not too bad! But there are a couple of areas where it could be improved:

  • Move to around 02:18. See the dark fringe on the first actor’s arm? That’s the result of decreasing Clip White too much. However, if you increase Clip White, you may start to see the background through the second actor’s head. Tweak this parameter to reach a compromise.
  • The edges around the actors are a little hard, especially when they are moving fast. Slightly increase Screen Softness to blend them better into the scene. If too much fringe starts to appear, you can balance this by decreasing Screen Shrink/Grow. (These two adjustments will also help the dark fringe problem.)

10.  The final step consists of a bit of color correction to better match the actors to their new environments. While still at frame 02:18 (where you can see the actor’s skin), click on the eyedropper for Despill Bias, then click on a pinkish skin area such as the left actor’s forehead. This will remove some of the green cast or “spill” caused by shooting on a greenscreen stage. It would be customary at this point to then spend time color correcting the foreground and/or background to better match each other, to help sell the illusion that the actors really were in this new room when the footage was shot. At a minimum, try using Levels to adjust the gamma and Hue/Saturation to adjust the hue. For more advanced color correction work, learn Synthetic Aperture’s Color Finesse, which comes bundled with After Effects CS4. RAM Preview; not bad, eh? Save your project, and have a nice cup of tea.

Our version is in Comps_Finished > 05_Keying_final. In it, we also key – framed Screen Softness to start out sharp when the actor is closest and getting softer later in the shot. Of course, you can spend a lot more time further finessing this shot – and those who do are the ones who earn the big bucks! These basic keying instructions can be applied to most shots. The overall goal is to do the least amount of damage to the outlines of the objects you want to keep. This comes with practice as well as compromise. If you have a series of shots taken with the same actors, lighting, and set, you may be able to reuse your keying settings, but most of the time you will have to approach each shot fresh. It takes a lot of patience and attention to detail to be a good visual effects artist, so it’s not for everybody – but films are relying on visual effects work more and more, so it’s a good skill to have.

Page 240   creating garbage mattes

When working with greenscreen footage, there may be extraneous objects that you don’t wish to see in the final composite such as mic booms, light stands, props, the edge of the stage, and so on. If they’re not also painted green, you will need to create a garbage matte to mask them out. Another reason to create a garbage matte is simply to reduce the area you need to key. For example, perhaps the corners of the frame are not as well lit as the center where your foreground is, making your keying job more difficult. A garbage matte could be as simple as creating a loose rectangular mask shape around your foreground; the mask does not need to follow the edges closely as the key will take care of that. If necessary, animate the mask throughout the clip by setting keyframes for Mask Path. For more intricate shapes, create a loose mask with the Pen tool. When there are multiple actors involved, you could even create one mask for each actor. Masking and animated masks were covered in Lesson 4. If you plan on doing more keying, we recommend the Composite Toolkit from dvGarage (www.dvgarage.com). It contains excellent training on how to make better composites, plus the dvMatte plug-in which works great with normally problematic DV footage.



Comments

No comments yet.

Add Yours

  • Author Avatar

    YOU


Comment Arrow




About Author

jamie

Instructor for Graphic Design 71