Refining the boundary across the initial span

You used the Roto Brush tool to create a base frame, which includes a segmentation boundary that divides the foreground from the background. After Effects applied the segmentation boundary across a span of frames. The Roto Brush span appears below the time ruler at the bottom of the Layer panel. As you move forward andbackward through the footage, the segmentation boundary moves with the foreground object (in this case, the flamingo).

You’ll step through the frames in the span and adjust the segmentation boundary as necessary.

_ Tip: To move forward one frame, press the 2 key on your keyboard; to move back one frame, press the 1 key.

1 Press the 2 key to move forward one frame.

Based on the base frame, After Effects tracks the edge of the object and attempts to follow its movement. Depending on how complex your foreground and background elements are, the boundary may or may not conform exactly to the area you hoped it would. In this case, you may notice changes to the segmentation boundary along the breast of the bird, near the feet, the tail feathers, or where the neck and body meet. This is normal, but it means you need to refine the segmentation.

_ Note: As it propagates the segmentation boundary for a frame, After Effects caches that frame. Cached frames have a green bar in thetime ruler. If you jump ahead to a frame further along the span, After Effects may take longer to process it.

2 Using the Roto Brush tool, paint foreground and background strokes to refine the matte for this frame. If the matte is accurate, you needn’t paint any strokes. As you move through the span, each change you make affects the frames after it. The more you refine your selection, the better the overall results will be.

3 Press the 2 key again to move forward to the next frame.

4 Use the Roto Brush tool to add foreground and background strokes as necessary to refine the segmentation boundary.

5 Repeat steps 3 and 4 until you reach 1:20. If the span doesn’t increase automatically, drag it forward to extend it beyond the initial 20 frames.

Дата добавления: 2014-11-20