Hi, I'm back on track :)
I always had problems with creating good fog from zdepth passes. Our 3d guys have the habit of rendering almost everything in one layer, so when I grade a zdepth pass and merge (over) it on top of the comp, often get some kind of a halo. The fog around objects in foreground, which are not covered, get wider thanks to grading the anti-aliased pixels. If I use an unfiltered depth pass, then I have jaggy edges. So it is always hacking with erode, blur and stuff, to make it more pleasing, probably you know that. But recently I discovered a quite good method. I use only 1 frame of a basic 3d fog (volume) rendered in deep. This frame I scale and transform and the make a holdout with the current shot deep render (yes, this is the only throwback, unfortunately we need that in deep), and that I use as a fog. I don't use any contrast modifier in order not to ruin the edges, just some coloring. Because the 3d fog doesn't have any noise in it, doesn't have to be rendered for each shot and every frame. 1 frame is enough. After this setup I can use some noise on cards to break it up (brightening/darkening with the noise as masks), in order not to look so uniform.
Of course I can use this for creating depth-based masks for color grading of the areas. Here you can see some images of this method, and if you are interested I can attach my deep fog sample, and my basic setup. Let me know in comments.
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Old graded Zdepth method (left) vs. deepfog method (right) with a character in front. Notice the hair
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| Node setup |
The control node has offset and multiply values, with that you can control the coverage of fog. Here you can see two different settings:
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| Depth mask with different settings, offset and multiply. |
Adding some slight variation with noise:
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| Detail with noise |
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