How To Select The Subject In After Effects - Tutorial

To isolate and refine subjects in After Effects, utilize tools like the Roto Brush, Fast Mask, and Content-Aware Fill, adjusting as needed for precision. For intricate tasks, manual rotoscoping offers the highest level of accuracy, allowing for frame-by-frame adjustments to achieve the desired outcome.

October 6, 2023
How To Select The Subject In After Effects - Tutorial
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Select The Subject (Main Object) In Your After Effects Composition

When creating background or foreground effects in After Effects, the challenge often lies in isolating specific subjects or elements. Achieving a clean and precise selection can be the difference between a professional-looking composition and one that appears amateurish.

What This Article Covers:

  • Tools for Automatic Selection: Understand the power and application of the Roto Brush and Fast Mask tools.
  • Content-Aware Techniques: Learn how to seamlessly remove unwanted elements from your footage.
  • Manual Precision: Dive into the art of manual rotoscoping for those times when you need the utmost accuracy.
  • Practical Examples: Real-world scenarios to help you visualize and apply the techniques.

Roto Brush Tool: Selecting Your Subject

The Roto Brush tool is your go-to tool in After Effects when you want to isolate a subject from its background. Think of it as a magic wand that can identify and select the subject you want to work on.

Step-by-Step Procedure: Using the Roto Brush Tool

  1. Locating the Tool: On the top toolbar, you'll find an icon that looks like a paintbrush. That's the Roto Brush tool. Click on it.
  2. Selecting Your Subject: Once you've selected the tool, move over to your composition. Click and drag over the subject you want to select. As you do this, you'll notice a purple outline forming around your subject. This is After Effects identifying and selecting your subject.
  3. Refining the Selection: Sometimes, the tool might select areas you don't want or miss out on some parts of your subject. To subtract from your selection, hold down the 'Alt' key (or 'Option' key on Mac) and paint over the areas you want to deselect.
  4. Adjusting the Selection Over Time: As your subject moves in the footage, the selection might need adjustments. Move forward frame by frame using the arrow keys and adjust the selection as needed.

Fast Mask Tool: Quick and Accurate Selection

The Fast Mask tool is a newer addition, designed to make the selection process smoother and more accurate, especially for moving subjects.

Step-by-Step Procedure: Using the Fast Mask Tool

  1. Locating the Tool: This tool isn't directly on the toolbar. Instead, you'll find it in the 'Effects & Presets' panel. Type "Fast Mask" in the search bar, and you should see it pop up.
  2. Initiating the Tool: Drag and drop the Fast Mask effect onto your footage in the composition.
  3. Making the Initial Selection: Using boundary points, outline your subject in one frame. These points act as markers, telling After Effects what you want to select.
  4. Propagation: Once you've made the initial selection, click on the 'Propagation' button. This tells After Effects to apply the mask across multiple frames, adjusting as the subject moves.

Think of the Fast Mask tool as tracing paper. You draw an outline on one sheet, and it gets replicated onto the sheets below, with minor adjustments for movement.

Content-Aware Fill: Removing Unwanted Elements

After you've selected your subject, you might want to remove unwanted objects from the background. The Content-Aware Fill does this by analyzing your footage and filling in the gaps.

Step-by-Step Procedure: Using Content-Aware Fill

  1. Locating the Panel: On the right side of your After Effects interface, you'll find a panel labeled 'Content-Aware Fill'. If you don't see it, go to 'Window' in the top menu and select 'Content-Aware Fill'.
  2. Using the Tool: Once you've made a selection using the Roto Brush or Fast Mask tool, go to the Content-Aware Fill panel and click on the 'Generate Fill Layer' button. After Effects will analyze the footage and remove the selected object, filling in the background seamlessly.

It's like using an eraser on a drawing. The Content-Aware Fill erases the unwanted object and fills in the gap with the surrounding colors and patterns.

Manual Rotoscoping: Precision at Your Fingertips

When automated tools fall short, manual rotoscoping is your precision instrument. It's the process of manually drawing and animating masks frame by frame.

Step-by-Step Procedure: Manual Rotoscoping

  1. Creating a New Mask: Select your footage in the composition. Then, using the pen tool from the top toolbar (it looks like a fountain pen), start drawing around your subject.
  2. Animating the Mask: Once you've drawn the mask, open the 'Mask' properties under your footage layer. Here, you'll find the 'Mask Path' property. Click on the stopwatch icon next to it to start keyframing. As your subject moves, adjust the mask for each frame.
  3. Feathering for Smoothness: To make the edges of your mask smoother, increase the 'Mask Feather' value in the mask properties.