One of the additions to After Effects CS5 is their Roto Brush tool. This tool can be considered their short cut quick take for the tedious process of rotoscoping. How often we want to extract something or someone from our video, mix up the images from different videos. The Roto Brush tool offers a quick method with very impressive results for achieving this end!
After Effects CS5 also includes Mocha which is a much more ambitious tracking tool but for basic cut and isolating objects for special treatment you will like their Roto Brush tool. Pick a video that is a good candidate for you. Pick something that has an object you would like to isolate and for this exercise, and we will do something, something to separate its treatment from the rest of the video. You could change its color or apply a color effect like changing its hue but choose something that is easy to work with and an effect that is easy to distinguish.
There are many ways you can put the Roto Brush tool to work for you but we want, in this exercise, to highlight how it works so you can better understand the possibilities. Once you have created a composition with a short video, one with a nice candidate for isolation, make a copy of your video so you can apply this new effect to one copy. Think of this effect as a mask, a smarter moving mask depending on the area you define.
Double click your copy to bring it up in the layer window which is where you apply the brush effect. Looking at your tools menu, at the far right, just to the left of your puppet pin tool you will see the Roto Brush tool. It is easy to use and you basically just paint the interior of the object you want to isolate. In my case, I am wearing a black hat, I will brush the interior of the hat to 'choose' it.
As you begin to apply the brush, notice that dragging your mouse diagonally will adjust its size making the brush size larger and smaller for your choosing target. As you choose your object it will be highlighted with a pink outline showing you what will be included. Like many similar tools, this is using pixel relationships so as you make your choice you can zoom in and fine tune your selection. If you have some area you want to remove from your selection, holding 'alt' key will switch to a 'subtractive' mode letting you highlight what you want to remove.
Once you are pleased with the outline of your brush mask, notice the 'Freeze' button under the timeline in the layer panel. This will capture your selection. Also notice the number of frames you have chosen under the timeline. You can drag this selection to the right or left to increase the time presence of your mask.
With the selection and time frame you want, return to your composition window and we will apply something to our selection to illustrate how you can treat only the section you have captured with your Roto Brush exercise. Remember, we began by copying our video to have the original and one for applying this effect. In my case, I isolated my black hat, and back in the composition, applied the fill effect under the 'Generate Effects' to turn my hat red. With fill applied, now my black hat has turned to red for the duration of the time window I 'froze' in the layer panel. Make sure the layer you have applied your Roto Brush to, and the one you will apply this new effect to, is on top of the copied layer. You want this effect to stand out. It will only be applied to the area selected by your Roto Brush but will only appear if it is on top of the duplicate layer.
Like all effects that require more than understanding, the Roto Brush effect definitely requires a bit of practice. Choosing a 'likely candidate' with nice color and light definition to make it easy to distinguish your shape certainly helps a lot. With a little practice, this tool, new to CS5 can go a long way providing flexibility mixing up and especially applying special treatment to portions of your videos.
Inspire, think globally, act locally. Web Designer Tom Womack uses Adobe Creative Suite 5 and Cinema 4D 12.0 creating dynamic sites with rich media.
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