Understanding the Roto Node in NUKE 9

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The Foundry’s NUKE is at the forefront for leading compositing programs in visual effects for television and film. Great news for those of you who want to learn NUKE and be ready for professional studio work. There is a FREE, non-commercial version to download. Once installed, you are ready to take on this tutorial and learn the functions of the roto node in a node based compositing program.

PLEASE NOTE* I have covered the topic of rotoscoping in basic and advanced tutorials previously in other compositing programs – Adobe After Effects & Silhouette FX. This tutorial is for those coming in with the knowledge of what rotoscoping is, but need or want to learn the interface of NUKE, since it is a node based compositing program. If you want to learn more of what rotoscoping is, please refer to my older lessons where I spend more time explaining the concept of rotoscoping.

I will break this tutorial down into three parts:

–       Adding the Roto Node

–       Shapes and Splines

–       Keyframing Shapes Over Time

ADDING THE ROTO NODE

Go to the DRAW NODES on the left hand side node bar > CLICK > and select ROTO. In your Node Graph, a roto node will appear. Simply hook up the viewer to the roto node in order to proceed.

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For those of you who are used to stacking layers in other compositing programs, such as After Effects, this might take some getting used to. Though the concepts remain the same, with node tree you are essentially mind mapping your ideas that are connected. I will go into more detail on Node Trees in another lesson.

SHAPES AND SPLINES

In your viewer, you can CLICK and create an anchor point. Continue to click around and you will start creating a shape. You can close the shape by either clicking back onto the first anchor point you created, or by simply hitting the ENTER key at any time.

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With the roto node active, on the left side of your viewer you will see your curves selections. The most commonly used are Bezier and B spline, but feel free to experiment with them all.

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Above the curves selection you will find your selection tools. These will control how and what you select of your splines in the viewer. For example, SELECT POINTS will allow you to select anchor points without selecting the splines themselves. Again, I encourage you to explore and tinker with all the tools to become familiar.

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In your properties window to the right, you will notice a list of shapes you have drawn in your viewer which will help you keep organized and remember which spline was used. Additionally, next to the shape name you have the EYE ICON which turns the shapes visibility on or off. Next to that is the LOCK ICON, allowing you to lock individuals shapes. That way they cannot receive or remove any keyframe data that has been established to that point. Next to that is the COLOR ICON which allows you to double click and choose a new color for that shape. The rest we will explore in a later lesson.

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KEYFRAMING SHAPES OVER TIME

Now let’s take a look at how we can start to animate these shapes across a timeline. By default the AUTO KEY feature is enabled. This is the skeleton key icon you see in the upper left hand corner near your selection tools.

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With this feature enabled, you can look at your frame on the timeline and see there is already a blue keyframe placed there.

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You can take your mouse and move the playhead further down the timeline, and then make adjustments to your shapes. You will notice another keyframe is automatically added (notice at frame one, and then again at frame 20, there is a blue dash representing the keyframe).

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Using your selection tools, you can move each control point individually, or you can highlight some or all of the control points on the shape and move those as needed. Additionally, you can go to your PROPERTIES window on the right and open the TRANSFORM tab to bring up the transform controls on your shapes. This will allow you to create separate transform keyframes on the timeline that handle transform, scale, and rotation.

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Rotoscoping with Silhouette FX

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Rotoscoping is the process of tracing over footage, frame by frame, in order to create a matte to be used as an element for compositing over another background. Think of it this way; say you have a three second video clip of a golfer hitting a ball. If you wanted to place that golfer on an alien planet, or deep underwater, playing a round of golf, then you would need to go frame by frame tracing around the golfer swinging his club and then composite over the new background. Rotoscoping is a time intensive process. With the example of the three second video clip of the golfer, at the standard rate of 24 frames per second, that means you would need to rotoscope 72 frames to complete the sequence. In the past, I’ve showed you how to use the rotobrush in After Effects. However, with longer sequences, it’s better to use a dedicated roto program such as Silhouette FX. In this tutorial, I am going to show you the basics of roto with Silhouette FX in two simple steps:

– Breaking the image down into Shapes

– Moving Shapes throughout the Sequence

*Before we begin, if you need help setting up your shot, or need some initial background on Silhouette FX, I would recommend you refer to a previous tutorial I posted titled “Creating an Alpha in Silhouette FX” which you can review here.

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BREAKING THE IMAGE DOWN INTO SHAPES

Once you import your media and setup a new session, you will need to select your spline tool from the left hand side of the canvas window. Your options are B spline, X spline, or Bezier. Please note that if you intend to import the roto’d footage into NUKE for compositing, then you will want to avoid using the X spline tool as there seems to be issues with NUKE interrupting those particular splines. I would recommend going with the B spline in that instance.

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Whichever tool you decide to use is up to you, however, the technique is universally the same. A successful roto is built upon breaking the image down into a series of shapes. In this example of a video clip of some hands, I will focus on the left hand first and break down each finger into a series of ovals and curves that contours around the joints.

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This is because as the video clip progresses and the hand begins to move and flex, moving individual shapes located around the anatomical joints is much easier than trying to create one large outlining shape around the entire hand and trying to move that frame by frame. It doesn’t matter what the roto subject is – a hand, a face, a machine, a book – it is your job as the roto artist to visually break down the subject into a series of shapes and animate those shapes over the course of the footage.

MOVING SHAPES THROUGHOUT THE SEQUENCE

At the bottom of Silhouette you will see the TIMELINE. This is where you will be able to visually see all the keyframes and movements you are making with the shapes throughout the sequence.

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Here are the playback controls:

X – Move one frame forward

Z – Move one frame backward

L – play video forward

K – pause video playback

J – rewind video playback

You can also zoom in and out of your image with ‘I’ and ‘O,’ and SPACEBAR allows you to pan around the image as needed.

As you move forward frame by frame you will not be using the X spline or Bezier tool to move the shapes you created. Instead, you will be using the Transform tool or the Reshape tool:

T – transform Tool > creates a box form around your shape allowing you to manipulate the corners of the box in order to stretch and form the shape. This is ideal for most simple movements between frames. The more basic movements you make, the less chance there is for “jitter,” which is an anchor point from one of your shapes jumping around from being manipulated wrong throughout the sequence.

R – Reshape Tool > this tool allows you to manipulate the individual anchor points of each shape. This should be a last resort method of moving a shape and only needs to be used in shapes that have extreme changes that cannot be captured using the transform tool. An example would be an article of clothing where a wrinkle appears for a few frames and then disappears.

To summarize, you will be using the X and Z keys to move forward and backward one frame at a time and using the Transform tool to move the shapes to capture broad movements, or the Reshape tool to capture fine details. Once your finished, use the J,K, and L keys to playback the footage and watch the shapes to make sure they stay on track with the roto subject. If there is an issue, simply stop the play back and make the adjustment as needed.

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