Using Z-pass Renders

BriReddBriRedd Website User Posts: 98 Just Starting Out

Does anyone here use Z-pass renders in Hitfilm? If so, what is the best method to do so.

Comments

  • BriReddBriRedd Website User Posts: 98 Just Starting Out

    Anyone? Anyone? Bueller?

  • Triem23Triem23 Moderator Moderator, Website User, Ambassador, Imerge Beta Tester, HitFilm Beta Tester Posts: 18,304 Ambassador

    I haven't directly used Z-passes, but here's some commentary based from theory.

    The Z-pass is giving you a grayscale image based off camera distance--white is closest, black is farthest.

    Traditionally, a Z-Pass would be fed to a compositor for generating occlusion maps. Something Hitfilm attempts to avoid via 3D Unrolled space. That said, I've had many times in Hitfilm 3 and 4 Pro where I've used alternate methods in Hitfilm to generate occlusion maps (For example, creating all white and all black versions of a 3D object and using the black/white versions in an embedded Composite Shot in 3D unrolled mode to create the occlusion map to bring into the main comp--allowing my main models to comp in 2D mode so I can put effects on them. I've also used Depth Fog to generate Z-passes).

    So the use of a Z-pass is to help occlude 3D elements or to add control to post processes like Lens Blur.

    In general to use a Z-Pass you'll need to put it into an embedded Composite Shot for processing. The Z-Pass itself becomes a control map for effects. For occlusion, you're using the Z-Pass to generate a Set Matte source, and for effects you're (again) either using Set Matte, or as a source layer within an effect.

    Right: so with maps black equals no effect, white is maximum effect, yes? But the Z-Pass has white closest to camera and black farthest from camera--so we're putting the Z-pass in it's own comp to put effects on it. There are several options, but I'm only going to discuss Curves, because I feel it's most flexible.

    So we're making an occlusion map for particles. Great--we're going to use curves to adjust the grey range so that the white is where we want the particles and black where we don't. Basically we're remapping the black white values.

    Or we're using a Lens Blur effect. So, again we're using Curves to remap the grey of the Z-pass to be white where we want blur and black where we don't.

    Try looking at tutorials on using Z-passes in AE or Photoshop. It's pretty close to what you'd do in Hitfilm, except in Hitfilm we have to embed the Z-Pass to bake in the adjustments.

    Make sense?

  • BriReddBriRedd Website User Posts: 98 Just Starting Out
    edited April 2016

    @Triem23 - After three read-throughs you pointed me in a direction with a theory. Got it working!

    I have a rendered 3D clip with it's Z-pass and I wanted to integrate a clip of some smoke / fog into it. The piece of the puzzle I was missing was to pre-comp the Z-pass to bake in adjustments. I also used Crush Blacks & Whites instead of Curves to adjust the Z-pass though I will go back to see if Curves gives me finer control.

    Before you slip away I want to say, "Thank you!" Although, I suspect your attitude is more like the guy in this clip.

     

     

  • Triem23Triem23 Moderator Moderator, Website User, Ambassador, Imerge Beta Tester, HitFilm Beta Tester Posts: 18,304 Ambassador

    Well, as the meme goes--"... Always be Batman."

    Histogram and Curves. Both give finer control than Crushing. Think of it this way: Crush is a hard switch, Histogram adds a center point to make a three-point black/white gradients, and Curves is total control. For smoke/fog Crush might be too hard an edge, but it's proof-of-concept. In Hitfilm there are often three or more ways to accomplish the same task. ☺

    For the hell of it here's a Z-pass test I did back in Hitfilm Ultimate 2. (pre Hitfilm 3 Unified 3D Space)- - basically I used the Depth Fog for the Comp Shot. I set it to black, and adjusted the falloff to define the front of the dust cloud thing and a distance where I considered the dust opaque. I put a copy of my Star Destroyer (altered to be pure white) and camera  in that comp. This was Embedded, Inverted and used as a Set Matte source for the clouds. 

    Depth Fog only works for a set camera distance and Depth Fog parameters can't be keyframed. Since it was a static camera, it worked for the shot. 

    I also pulled it off with a moving shot. In this case I just had to plan the camera move around distance to successfully occlude the Atomic Particles layer with the 3D models 

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