Creating 3D Breakdown Based on Depth Case Study
Point Position Pass is one of the essential passes that you'll need and could save you a lot of time later on in Comp.
As we know, Position Pass is often used for relighting. Or if you do little bit research, it also can be used as one of the element to generate Point Clouds, and also you will need Normal Pass and 3D Camera from your 3D software for either of this technique. Little did i know, i found that you can remap it by using grade node (In Nuke) to remap the color information.
Creating cheap and fast fog/atmospheric look, creating Zdepth just incase you forget to include Zdepth into your passes, and making 3D breakdown based on Depth. In this article, I will be sharing more in depth about 3D breakdown based on Depth. You might have seen this kind of transition from VFX breakdown. But I haven't found any article/video specifically covering this technique. Here is the 3D breakdown that used depth as the transition instead of regular wipe that we usually see.
Jungle Book by MPC ( https://www.youtube.com/watch?v=e6yKWQ24rF8&t=155s )
This idea came up when i was helping a friend of mine, Darren Lesmana making his breakdown. Really nice and talented guy, you can check out his work here.
He was showing me some CG breakdowns that used this transition. The one thing that came to mind that time was Position Pass. Dealing with masking, and what you need just solid alpha black and white to create a matte. You can generate Point Position Pass from any 3D package softwares out there such as Houdini, Maya, etc.
Here's the result.
Recent prep (rotoscoping) work showing alpha in depth, roto was done in Silhouette FX, matchmove was done in PFTrack and Maya. Here i already provided simple render scene that you can download, so you can follow along.
Open or import the file into Nuke and create Shuffle Node. In the Shuffle Node, click drop down menu to select PositionWorld.
Press R or G or B to switch between RGB viewer. Each channel represents XYZ. For example:
R = X
G = Y
B = Z
In this case, we will be using Z. But feel free to play around with XY.
Next, we're gonna shuffle everything into blue channel, as we want to look in Z.
Let's say we want to make transition between AO and Beauty. Shuffle out Ambient Occlusion or whatever layer do you want. In this case, by default the original alpha is so subtle.
We need to switch the alpha from b channel to the other side.
Go back to your Position Pass and we're gonna need grade node to remap the color information by picking the screen color of your position Pass. Set the foreground and background by using color picker.
Remember! Pick the color information based on your Position Pass not your beauty channel.
You can always change the value by using the slider. And play around with it, until you find the setting you like.
Next, set the keyframe. Crank up the value at the first frame to pure black.
And set at the end of the frame you want to pure white. Always check in the middle between two keyframes to make sure you don't get the harsh edges. And also change the channel from rgb to RGBA to affect the alpha as well.
At this point, you'll be able to see the preview how smooth the transition you've set. You can also use Invert node to invert the transition and blur node to smooth the edges. The next step will be merging Beauty and AO by using merge node, and plug the mask input to grade that we've already remapped.
The result would be like this.
I'm sure there is always a better and unique ways to achieve this kind of transition. Feel free to get in touch! I'm still curious how do they approach this kind of transition in their actual breakdown.