Compositing On The Nimble Collective Platform

Ben Pre-production Art - Stevie Lewis

Pre-production design of Ben by Stevie Lewis

 

Ben Pre-production Art - Stevie Lewis

Pre-production design of Ben by Stevie Lewis

Creating Crunchy Grungy Matte Edges for Disrupted

Computer graphics are really great at creating nice crisp lines between objects.  For Disrupted, we wanted to create a very organic feel to the characters.  In this case, a hand-painted look to the objects in the scene was important in order to match the incredible pre-production art work.  Earlier, we covered how we matched the production art for our Animal Facts: Chicken short. Getting 3D renders to match 2D designs can be very challenging, and the Disrupted team went through a lot of trial and error to give Ben his signature “crunchy” look. One of the techniques we used to achieve this was to roughen up the edges of the alpha channel for the characters and their highlights.

Below you can see an example of what Ben looks like composited over a background plate without this effect.  Notice the crisp edge.

 

In this tutorial, we will go through the task of roughening up the edges using a nodal compositing workflow in Blackmagic Design’s Fusion 8.  While some of the techniques are specific to Fusion, you should be able to adjust them to pretty much any compositor you have access to.

As you can see below, the initial setup is pretty basic.  We have 3 images loaded into the node setup:  Ben, a background image, and an alpha mask for the counter.  Note: there’s also a gamma node applied to Ben in order to make sure we’re working in the correct color space.

These nodes are all connected through a Merge node which will give us the final result.

Looking closely at the alpha channel for Ben.  The white part of the image is what is going to be shown, and the black part is what will be hidden.  Notice how clean the edges are.  Let’s go ahead and mess them up!

Create Some Noise

The first step is to create some noise to eat away at the entire alpha channel.  This will ensure we understand how to play with what part of ben is visible, and what isn’t.

In Fusion 8 choose Tools -> Creator -> Fast Noise.  This will generate a noise node that you can start messing with.

With the Fast Noise node selected, hit 2 on the keyboard.  This will display the noise in the right viewer.

Scale It

Now it’s time to adjust the scale of the noise so it’s smaller and closer to what we want to use..  In the Tools panel, select the Scale control and bring it up to 350 or so.  This should make the noise nice and small so it feels more like scratchy paper.  You can play with this setting until you get the look you want.

Use the Noise as the Mask for Merge

Re-route your node graph so the noise is used as the mask input for the Merge node.  In this case I temporarily removed the counter_behind_alpha node, and will add that back in later.

Select the Merge node and hit 2 on the keyboard.  This will display the new noisy Ben on the right hand side of the viewer.  Remember, the white parts of the mask will show the foreground image (in this case, Ben), and the black parts will hide it.

As you can see, the noise is working, but it’s eating up too much of Ben’s body.  We really only want the edges of Ben being eaten away. To do this, we’re going to add back in Ben’s Alpha channel from the original image.

Adding Back Ben

Now we’re going to create a new merge node and add the noise and Ben’s alpha together.

Make sure you have nothing selected and choose Tools-> Composite -> Merge.

Now connect the output of the character and the output of the noise to this new Merge node.

To view what’s happening with the alpha clearly, select the character node and click 1. Then click in the left viewer and hit a on the keyboard.  This will toggle between looking at the alpha and looking at the color version of the image.

Now select the merge node and click 2.  Hover over the right viewer and hit a on the keyboard.  You should now be looking at the alpha for both images.

Make Ben Smaller

To make Ben’s mask smaller, we need to erode it a little bit.  To do that, we’ll use a Erode / Dilate node.  This node will shrink and grow the alpha channel.

Deselect everything in the node view and choose Tools-> Filter -> Erode / Dilate.

Connect the output from the character to the Erode / Dilate node, and then the output from the Erode / Dilate node to the input of the Merge node.

You won’t see much difference yet, but that’s because you haven’t changed anything.  Go ahead and start adjusting the Amount of the Erode Dilate node in the Tools panel.  

As you pull the control negative, you’ll see the alpha channel being eaten away.  For Ben, we found a value of -.0015 or so worked pretty well as a start, as well as changing the filter to Linear.

Use This Mask

Select the Merge node that has the character on top of the background.  Click 2 to put that node in the right viewer, and then click on the viewer and hit a to take it out of alpha mode.

You will see your character still eaten away completely by the noise.

Now take the Merge node that has the Erode / Dilate node connected to it,  and connect it to the mask of the original Merge node.  

The character will re-appear, but with a slightly softer edge.

Clamp the Noise

Now we just need to clamp some of the noise values to make sure they aren’t so soft.  You can do this with a simple color curve node.

Select the Merge that is leading into the mask of the final Merge node.

Choose Tools -> Color -> Color Curves

With the ColorCurves node selected, click 1 on the keyboard.  This will put the node in the left viewer.

In the Tools panel, grab the lower left control of the curve and slide it to the right.  As you do, you’ll start to see the noise get a bit crisper.

Then grab the upper right control and drag that to the left.

By playing with these values, you’ll start to feel the edges of your character get much crisper and more broken up.

For a more detailed explanation of how color curves work, I recommend reading this tutorial on Gimp’s color curves.  It really helped me understand it!

If the edge isn’t noisy enough, you can simply play with the Erode / Dilate node to push it to extremes!

As you can see from the final movie, we used this effect on the highlights for the character as well, really having fun playing with the different effects we could get!

Jason Schleifer
Jason Schleifer

Jason and his mad scientist eyebrows have been pushing the boundaries of CG animation and sharing his knowledge for nearly 20 years. Widely recognized as an industry leader and mentor to hundreds of animators, Schleifer, formerly of Weta Digital and Head of Character Animation at DreamWorks, now works as Head of Content and is a co-founder of Nimble Collective.

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