http://www.computerarts.co.uk/__data/arts_pdfs/tdw63.tut_ae2 by jorge mourinho

TUTORIALS | Compositing

● Realistic shadows and reﬂections help to lock a CG character – such as this Oil of Olay-challenged hitchhiker – within a shot. We’ll be explaining how to set them up below

AFTER EFFECTS

Art of darkness Subtle compositing touches help to sell effects shots like the one above. Follow our guide to adding realistic shadows and reﬂections to the scene BY CHRISTOPHER KENWORTHY

FACTFILE FOR After Effects DIFFICULTY Intermediate TIME TAKEN One hour ON THE CD • Full-size screengrabs • Source movies: • Poser 5 ﬁles: • Final animation ALSO REQUIRED Additional software such as Magic Bullet can enhance the ﬁnal effect

hings can get a bit complicated if you want to

moving background. You can create these shots by videoing your

place your 3D character in a real-world situation.

car in your garage. Even if you’ve no intention of doing your own

When there’s glass in your background plate,

compositing, the information contained with in it will still

you’ll need a realistic reﬂection. And if you want

prove useful when it comes to lighting and outputting characters

a dynamic shot with handheld camera movement, motion

for clients or compositors.

tracking will lock your character into place. Fortunately, the challenges of compositing, such as reﬂections

SUPPORTING RESOURCES

and handheld background plates, are also its strengths. This example

This issue’s CD (for details, see page 114) contains the Poser

of a clay man sitting in a car – a shot from a commercial video release

animation ﬁles for the clay man and his reﬂection, as well as a 3DS

called The Dream Sequence – wouldn’t look as good if the camera

single-frame ﬁle. To save time, we’ve also included the completed

was locked off: the handheld motion makes the shot seem realistic.

output footage. Carshot.mov is the handheld shot used as a

Equally, an angle could have been chosen with no glass reﬂections

background plate, and TreeBG.mov is a blurred background plate

but, by choosing to show a reﬂection, you can sell the shot. Adding a

created in Vue 5.0. The ﬁles ClayModel.mov and Reﬂection.mov

believable shadow to your scene is almost impossible, but you can

were output as Animation, complete with Alpha channels. You can

add one that will be perceived by your audience as being realistic:

see the ﬁnished shot in ClayManFinal.mov.

the shadow itself will be so subtle it won’t be noticed, but it helps create the illusion that the clay man is actually positioned in the car. This tutorial shows you how to composite your 3D character into background footage, with realistic motion and motion blur, plus a

Christopher Kenworthy is a writer and director living in Australia. He’s currently working on several ﬁlm and TV projects [w] www.thedreamsequence.com

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Compositing | TUTORIALS

STAGE ONE | Creating ﬁles for compositing

Your background plate should be shot using black material over the glass to make the window outline easier to see. Stick on two pieces of masking tape, with black dots drawn on, to provide a reference for motion tracking – these should be placed parallel to the ﬂoor. If you want, you can also sit somebody in this seat for lighting, reﬂection and size reference.

Although you can create your model and animation at any time, it’s wise to light the model once you’ve seen the background plate. People in real cars aren’t well lit, but there’s an accepted movie convention of using strong light from the front, with hard shadows at the back. The car was lit strongly from the front, so do the same with your model.

Use the same model and lighting to create a reflection output. Car windows tend to reflect an area from the knees to the shoulders, so position your camera accordingly. Output both animations as a DV Animation with Millions of Colours+. This creates an Alpha channel so, when you import the movie file, the background vanishes and the composite is already halfway there.

STAGE TWO | Anchoring the model to the background

With all your ﬁles imported to After Effects, create a new DV composition and add the Carshot.mov to the timeline. Set the Tracker controls to Track Motion. Check the Rotation box and apply a track point to each of the dots on the window, then click the Track Forward arrow. This records the motion of the camera, which will be applied to all other layers in order to simulate the car’s motion.

Next, drag the ClayModel.mov to the timeline and then Edit Target in the Tracker controls so the Clay Man layer is selected. Click Apply and choose Apply X&Y so that your clay man will move and rotate in time with the background.

Select the Clay Model layer and expand the Transform properties in the timeline. You’ll see that Position and Rotation have been set by the Tracker controls, but the clay man is in the wrong place. To move him to the correct place, drag the Anchor Point settings until he appears to be sitting in the right position.

Bear in mind that this shot is intended for 16:9 widescreen output, so it doesn’t matter if the incomplete lower edge of the man is visible. To test this, create a new composition called Test 16:9, drag your ﬁrst comp into this new timeline and draw a 16:9 matte box. This can be referenced through the tutorial.

Duplicate the Clay Man layer, press [Enter] and rename it Shadow. Apply a Gaussian Blur of about 8.0, and then apply Brightness and Contrast, with both set to -100. Drag the Shadow layer below the ClayModel.mov layer so the shadow will appear behind the clay man, but over the car seat.

You can’t rotate or drag the shadow into place because rotation and position keyframes control the layer’s motion. Instead, apply the CC Power Pin ﬁlter and drag the position markers. The shadow should appear to lean backwards, away from the man. Change the Blending Mode to Multiply and reduce Opacity to 50%.

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TUTORIALS | Compositing

STAGE THREE | Creating a view through the window

Drag the TreeBG.mov clip into the timeline, above the carshot but beneath the clay man and the shadow. Click the eye icons for the clay man and shadow to make them invisible, and set the Tree layer Blending Mode to Add so you can see what you’re doing as you work.

Select the Clay Model layer, press [P] to reveal the Position data, click-drag around all the position keyframes, and Copy. You want to transfer this data to the Tree layer, so select the layer, press [P], make sure the Current time Indicator is at the beginning of the sequence and Paste.

At this stage, if you don’t apply rotation data as well, you’ll get a slightly different look to your scene. It’ll look as though the camera is bouncing around inside the car. For this version, we’ll make all the rotations match. Select the Clay Man layer, press [R], select and copy the rotation keyframes and then apply them to the Tree layer.

If you play the clip through, you’ll see that the Tree layer matches the movement of the car pretty well, but it’s in the wrong position. Again, the solution is to adjust the anchor points. Press [A] and drag the anchor settings until the layer covers both of the side windows.

When you’ve dragged the anchor settings until the layer covers both of the side windows. Select the Tree layer and use the Pen tool to draw a mask around the window. You’re actually cutting a mask out of the Tree layer, but using the car window for reference. When the mask is completed, the trees will appear to show through the window.

Repeat the same masking procedure you performed in step 14 for the rear passenger window. You can feather both of these masks by selecting the Mask, pressing [F] and adjusting the Feather to about 2 pixels, just to soften the edges. However, the window markers are still showing, so to get rid of them, change the Blending Mode of the Tree layer to Normal.

STAGE FOUR | Adding reﬂections to the glass

After you’ve changed the Blending Mode of the Tree layer to Normal, drag the Reﬂection layer to the timeline. Make sure you place it above the car and the trees, but below the clay man and shadow. It’s also better to keep the clay man and his shadow invisible while you work so as not to confuse things. Set the Blending Mode of the Reﬂection layer to Add.

Using the techniques you learned earlier, copy the Position and Rotation values of the Clay Man layer to the Reﬂection layer. You can also switch on the Clay Model layer (by clicking the eyedropper) to ensure that the motion of the two clips matches.

Select the Reflection layer, press [A] and adjust the reflection anchor points until it’s roughly positioned over the window. Most of this reflection will be hidden behind the clay man himself, so you can position the layer slightly farther forward than is realistic. This means that a little more will be visible.

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Compositing | TUTORIALS

STAGE FIVE | Bringing everything together for ﬁnal output

Press [S] and adjust the scale of the reﬂection until it looks more accurate. You’ll need to readjust your anchor settings. It’s best to adjust the scale with the model in roughly the right place, which is why you anchor, then scale and re-anchor. It seems like a waste of time, but it leads to better results.

With the Reﬂection layer selected, use the Pen tool to draw a mask around the window. Press [F] and feather a couple of pixels. By itself, this reﬂection, at full opacity, looks unrealistic. Even the angle seems strange, until you check your reference footage of a real person sitting in a car. The next step will bring the required realism.

Adjust the Opacity of the Reﬂection layer to about 25%, and change the Blending Mode to Screen. Click the eye icons for the Shadow and Clay Model layer and you’ll get a good impression of the end result. A RAM preview will show you how movement, shadow and reﬂection combine to make the man appear as though he’s in the car.

Your ﬁnal output is rarely the ﬁnal output! To make the composite really work, remember that the colours will have to match other shots in the scene. You should, however, keep a master copy of your output, then re-import this to After Effects or your editing application so you can begin colour grading and additional effects. Filters such as Magic Bullet (available from Red Giant Software:

www.redgiantsoftware.com) can add a fuzziness and motion blur that gives more of a ﬁlm effect. This helps to reduce the CG look, and makes the clip blend in better with the rest of your sequence. Although CG and real-world blends are rarely realistic in the strictest scientiﬁc sense, you can create an impression of complete realism for your audience with these techniques. ●

Check the M boxes in the timeline to switch on Motion Blur for all layers. Also click on the M button just above and to the right, which will make Motion Blur visible as you work. Motion Blur takes time to render, so it’s best to leave it until the end. Another RAM preview will reveal a huge improvement to the clip.

You need to letterbox your output to 16:9 widescreen. You can apply a Letterbox ﬁlter, if you have one, or go to your Test 16:9 Widescreen comp and use that for your ﬁnal output. Check that no unwanted edges drift into the frame.

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