This chapter is from the book
This chapter is from the book
This chapter is from the book
Fine-tuning the matte
Roto Brush does a pretty good job, but there may be stray bits of background in the matte, or foreground areas that weren’t included. You’ll clean those up by refining the edge.
Adjusting the Roto Brush & Refine Edge effect
When you use the Roto Brush tool, After Effects applies the Roto Brush & Refine Edge effect to the layer. You can modify the effect using settings in the Effect Controls panel. You’ll use those settings to further refine the edge of the matte.
Press the spacebar to play the clip in the Layer panel. Press the spacebar again to end the preview when you’ve seen the whole clip.
As you preview the clip, you may notice that the segmentation boundary jumps around a bit. You’ll adjust the Reduce Chatter and Contrast settings to make it smoother.
In the Effect Controls panel, decrease the Contrast to 40% and increase Reduce Chatter to 20%.
In the effect controls panel. the Roto Brush & Refine Edge effect is active. Under Roto Brush Matte, the Contrast has been reduced to 40% and Reduce Chatter has been changed to 20%. All other options are at their default settings.
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The Reduce Chatter value determines how much influence the current frame has when performing a weighted average across adjacent frames. Contrast affects how tight the boundary is.
Preview the clip again.
Using the Refine Edge tool
When an object isn’t smooth, the Roto Brush may not pick up the nuanced edge. The Refine Edge tool lets you include fine details such as wisps of hair in designated areas of the segmentation boundary.
Though it might be tempting to use the Refine Edge tool immediately after creating the base frame, it’s best to wait until you’ve refined the segmentation boundary across the entire clip. Because of the way After Effects propagates the segmentation boundary, using the Refine Edge tool too early results in a matte that is difficult to use.
Go to the base frame, which is the first frame of the clip, and then zoom in so that you can see the edges of the bird’s tail clearly. Use the Hand tool if necessary to move the layer so you can see the entire bird.
Select the Refine Edge tool (
), hidden beneath the Roto Brush tool in the Tools panel.
The tail is relatively soft, so a small brush size will work well. For a fuzzier object, you might have better results with a much larger brush. The brush needs to overlap the stray edges that emerge from the object.
Change the brush size to 5 pixels.
When you use the Refine Edge tool, draw strokes along the edges of the matte.
In the Layer panel, move the Refine Edge tool over the edge of the tail straddling the segmentation boundary and including the variations in the feathers. You can use multiple strokes if needed.
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The first stacked image shows the Refine Edge brush being applied to the tail. The second stacked images shows the X-Ray view of the applied Refine Edge. The right image of the brushes panel shows a 5 pixel brush with 100% hardness selected. All other options are at their default settings.
When you release the mouse, After Effects switches to the Refine Edge X-ray view so that you can see how the Refine Edge tool changes the matte, capturing the detail in the edges.
Move the current-time indicator across the time ruler to view the edge. At 0:15, Refine Edge breaks away from the tail as the bird moves away rapidly.
Change the brush size to 19 pixels.
At 0:15, press Alt (Windows) or Option (macOS) and erase the artifact from the Refine Edge tool, as it’s no longer useful going forward.
Continue to move forward and backward through the scene, applying the Refine Edge tool wherever the matte’s edge doesn’t capture the fuzziness of the bird’s feathers, and removing it wherever it strays from the tail.
The first stacked image shows the erasing the Refine Edge remnents brush since it’s no longer tracking correctly or needed. The second stacked image shows the result with the refine edge matte removed. The right image of the brushes panel shows a 19 pixel brush with 100% hardness selected. All other options are at their default settings.
Zoom out to see the entire scene, resize the Layer panel if you enlarged it, and then choose File > Save to save your work.
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