Adobe After Effects CS3 Manuel d'utilisateur télécharger pdf (Page 275)

AFTER EFFECTS CS3

User Guide

270

• To key well-lit footage shot against multiple colors or unevenly lit footage shot against a bluescreen or greenscreen,

start with the Color Range key. Add the Spill Suppressor and other effects to refine the matte. If you are not

completely satisfied with the results, try starting with or adding the Linear Color Key.

• To key dark areas or shadows, use the Extract Key on the Luminance channel.

• To make a static background scene transparent, use the Difference Matte Key. Add the Simple Choker and other

effects as needed to refine the matte.

For tips on shooting footage so that color keying is easier and more successful, see Jonas Hummelstrand’s website:

www.adobe.com/go/learn_ae_jonasshootingforcolorkeying.

See also

“Keying effects” on page 440

“Matte effects” on page 450

Use a garbage matte

A garbage matte removes unneeded portions of the scene, resulting in a rough area that contains only the subject that

youwanttokeep.Whenyouareworkingwithapoorlylitorunevenbluescreenorgreenscreen,sketchingagarbage

mattearoundthesubjectcangreatlyreducetheamountofworkthatyouhavetodoinkeyingoutthebackground.

However, if you spend a lot of time making a perfect garbage matte that exactly outlines the subject—essentially

rotoscoping—you lose the time-saving advantage of color keying.

1 Create a mask to roughly outline a subject.

2 Apply one or more keying effects to mask out the remainder of the background.

3 Apply Matte effects as necessary to fine-tune the matte.

Aharon Rabinowitz shows how to create a super-tight garbage matte using Auto-trace in this video tutorial:

www.adobe.com/go/learn_ae_aharonsupertightmattes.

See also

“Creating and importing masks” on page 254

“Keying overview and tips” on page 268

“Matte effects” on page 450

Use a hold-out matte

Use a hold-out matte (also known as a hold-back matte) to patch a scene to which a keying effect has been applied.

A hold-out matte is a masked-out portion of a duplicate of a layer that you have keyed. The duplicate is masked to

include only the area of the image that contains the key color that you want to preserve as opaque. The hold-out matte

is then placed directly on top of the keyed layer.

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