Rotoscoping to Replace a Foreground Element in Resolve Fusion

Day 20: 25 Insights in 25 Days 2019 New Year Marathon!

Part 2: Adding a foreground back using Masks and keys

In Part 1 of this topic we looked at how to remove an object from a scene using the Paint tool and the Clone brush. Now we need to add back any foreground elements which had been removed by the Paint tool – in this case its the girl’s hand as it goes over the area where the glass was.

It’s often a good idea to use several different Masks if you have a complex shape, like a body with limbs and a head. It’s much easier to treat these separately than trying to animate a single mask with a complicated outline of the person.

Instagram: Using multiple shapes

You’ll notice that I try to use as few keyframes as I can, only key-framing at a point when the natural motion changes but I then go back and see if I need to add extra keyframes in between.

Bezier vs. B-Spline

I usually opt for Bezier curves for everything but I’ve recently been trying to use B-Splines as an alternative because the handles on Bezier curves can need lots of tweaking when doing roto like this. The good news is that Fusion lets you convert your shape after you’ve made it if you change your mind. Right click in the viewer with the BSpline selected and there are a ton of options under the BSpline:Polyline> menu including ‘B-Spline to Bezier’ (or the other way).

You can manipulate the control points on your polyline by dragging a lasso over the desired points and then;

• Hold T while dragging to rotate the points about the point where your mouse is dragging.
• Hold S while dragging to scale the points, centred on the point where your mouse is dragging.
• Shift + B will turn on a bounding box around the selected points. You can then drag the edges of the box to scale it, hold shift to move the individual corners of the box and hold cmd (or ctrl) to size it, scaling from the centre of the box.
• Update: Hold W while dragging to control the ‘weight’ of selected control points in a B-spline

Temporary CC tool

I’ve found that having a Colour Corrector tool in the flow which I can turn on and off really helps me to know exactly where my shape is that I’m replacing (be sure to turn it off before you render!). I use a dummy colour corrector in all sorts of situations when doing invisible fixes, just to make my fix visible for a moment to see what’s going on.

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• January 20, 2019 at 6:30 am #32785
  
  Jamie Dickinson

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  This is the discussion thread for the Insight: Rotoscoping to Replace a Foreground Element in Resolve Fusion

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  Willian Aleman

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  January 21, 2019 at 4:04 pm

  Jamie, thanks for the great insight. I would like to see more Resolve and Fusion insights dealing with occlusions between subjects and objects. This is the harder task I was confronting in Resolve while trying to use Match Move in a recent project. Tracking an object with forthground occlusions was a failure in Resolve.
• 
  Jamie Dickinson

  Guest

  January 21, 2019 at 8:07 pm

  Hi, William – basically the same methods apply, create a new background using the clone brush/freeze/tracker, etc. then key the bits of the foreground that you still want back on top. And where the keying fails (which it inevitably will) you use tight masks and and careful keyframing. If you can’t get a good key around hair, for example, then masking that will be really difficult. Fusion lets you combine all these tools in different areas of the picture (see my earlier Insight on combining keys).
• 
  Willian Aleman

  Guest

  January 22, 2019 at 3:06 pm

  Hi Jamie – Thanks for the prompt response. Because I have several projects running in Resolve 14.3, I haven’t upgraded to 15 version. So, I don’t have Fusion installed yet. I’ll try your suggestions and workflows shown in your Fusion series in future projects. As you already know, for the immediate need of my current project I’m passing this task to a Fusion specialist.
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