Changing the background
There are many reasons to isolate a foreground image from a background. Often, you want to replace the background entirely, moving the subject to a different setting. But rotoscoping is also useful if you simply want to change the foreground or background without modifying the other. In this lesson, you’ll make the back-ground blue to enhance the wintry theme and help the subject stand out.
Close the Layer panel to return to the Composition panel, and then move the current-time indicator to the beginning of the timeline. Choose Fit from the Magnification Ratio pop-up menu at the bottom of the Composition panel.
The Composition panel displays the composition, which includes only the boy.mov layer, consisting only of the foreground you isolated from the clip.
Hide the properties for the boy.mov layer, if they’re visible.
Click the Project tab to display the Project panel. Then drag another copy of the boy.mov clip from the Project panel to the Timeline panel, and place it below the original boy.mov layer.
Click the new layer, press Enter or Return, and rename the layer Background. Then press Enter or Return again.
With the Background layer selected, choose Effect > Color Correction > Hue/Saturation in the After Effects menu bar.
In the Effect Controls panel, do the following:
Change Colorize Hue to −122 degrees.
Change Colorize Saturation to 29.
Change Colorize Lightness to −13.
Choose File > Increment And Save.
If you save incrementally, you can return to earlier versions of your project to make adjustments later. This can be very useful if you’re experimenting or want to try alternative effects. The Increment And Save feature preserves the previously saved version of the project and creates a new project with the same name, with an increasing number added to the filename.