073 Fog

- [Steve] Hi this is Steve Wright welcoming you to this week's Nuke Nugget, fog. We often have to make wispy things like fog, smoke, mist, and vapor, so here are some techniques to help you make your fog foggier and your mists mistier, using the noise node. All right, so here I've got a little fog thing set up here for you. So I'm going to walk you through the various techniques I use to try to help make this look a little bit more than just a slab of flat noise.

Starting with the noise node set ups, I'll hit the the viewer directly to the noise node, and the XY size of course is you know what size you want your, your fog lumps to be. So I chose a size I thought worked well with my picture. Okay, one thing that I did that was interesting was that I turned up the lacunarity. Lacunarity is sort of like adding extra detail to the picture. For example, I'll put it back to default here. There, you see there's the default, and there's the extra lacunarity.

So don't be afraid to dial that guy in. Now, we needed a translation. The thing had to move across the screen. So to do that I used the transform tab and put in a translation of you know just zero on the first frame and 70 on the last frame, no big. But I did something else that was interesting, a skew, a skew. Here's the deal, when you have a fog, let's get back to our background plate, the fog is moving across the ground here, but when it drags across the ground it moves more slowly on the ground than it does up in the air.

So, I threw in a little thing here, this skew factor like so, all right, animated at the beginning. It skews to the left by minus .1 and at the end to the right by plus .1. What that does is that makes the top part of the picture move a little faster than the bottom part. I think you can see that. Very important point about the skew. You have to put your pivot point down here at Y equals zero.

See, right there. If the pivot point is up here in the middle of the screen it's going to skew both the top and the bottom. Don't want that. And for the color I just left it at default, because I'm going to control that separately. Okay, we're done with the noise node. We'll put that away. Let's take a look at this grade node here. Here's what's going on. We'll hook up my viewer to this grade node. Let's push in a little bit here, and I'll re-home the viewer.

The idea here was to have specific controls over the RGB layers. With the lift I can reduce the density of the dark spots. You see, you can't do that with the color tab of the noise node. All you can do is adjust what amounts to the gain. So, putting that back to where I had it, and then I have a gain control here, so I can make the hot spots, or the bright spots, just as bright as I want, and the lift allows me to control those dark spots separately.

Next, I threw in a shuffle node in order to kill the alpha channel, here. Fill alpha with zero, and here's my alpha channel now. So I could follow that with this grade node here which talks to just the alpha channel. What that allows me to do, hooking the viewer up there, looking in the viewer window here, the offset. I can set the density of the alpha channel between zero and one. So this gives me control over the alpha channel density which gives me control over the transparency because I'm following that with a pre molt, okay? So now here's my alpha channel offset.

So if I make the alpha channel go towards zero it goes completely transparent. I'll bring it up to one. It goes very opaque. Now let's see how that looks over the background plate. So let me hook my composite node here up to there. Now I can thin out or thicken up my transparency separate from the RGB settings, and this is the whole name of the game here is control.

The key to making an effect like this look more realistic is complexity, okay? So what makes stuff look fake is it doesn't have the complexity of the real world. So we're trying to put as much control and complexity into it as possible. Now, putting this over the background plate, I did a little thing here. Here's my background plate. I added this roto node in order to fog the distance. So this is like kind of a little depth effect that I put in, and then I laid the fog on top of that.

You see if I turn that off, the fog looks like it's just laid right on top of the picture, which is a common mistake made by many. It should get more dense with depth, and to do this, this was a very simple gag. Let me hook that up there. Okay, let me pull out just a little bit here. So all I did was I drew a rectangle right around this part of the picture here, and then pulled out the feather points, okay? So I'll select that.

You can see I pulled out the feather points, which gave me a nice gradient. In fact, you can see the gradient if I just do a replace operation. In addition to that, by setting the RGB value here I can increase and decrease the brightness of it and then separate from that we have the transparency of it. So again, maximum control, okay? So let me get rid of that overlay.

So, I can dial in now, selecting that. We can dial in how bright it is, or dark it is, and then again, because we have the separate control here we can dial the transparency or opacity up and down to get the look we want. So that forms kind of a background over which this foreground fog is laid. So you see it makes a huge difference in the appearance.

Okay, one last thing I did that I think you'll enjoy. Here is an eye distort node, okay? Let me push in on this. Look what happens, what I did with the eye distort node. I used this eye distort to introduce a fake parallax into the shot. Let me zoom out a little bit. As this fog bank was moving across the screen it's supposed to have some depth to it, right? It's not just supposed to be sitting on a flat card. So the parts of the fog that are closer to the camera would traverse the screen a little faster than the parts of the fog that are further away.

So that's the parallax I'm talking about. This introduces that parallax. The distortion pushes bright areas like this to the left when they're over here, but as they cruise across the screen they start getting pushed towards the right, but only the bright parts of the picture. In fact, let me show you. Let me zoom in here, and I'll toggle the distort on and off. So you can see, like right here, this area is not moving but this area is moving quite a bit, okay? So we're not distorting everything.

We're only picking up the bright parts and pushing them to introduce some parallax with the dark background area. So here's how we did that. Starting with our original noise, we take it to a grade node and use that to drop out the blacks, okay? By taking the black point I can drop the blacks down which means these areas are not going to get displaced, okay? The white point here allowed me to pull it up so I get a little more density out of it.

Okay, we then hit that with a blur just to soften things, so that it doesn't have sharp edges. Now, this is going to become my motion UV map for the displacement. However, remember that what we want to do is, let me get this guy selected here, so on the left side of the picture I want to push my picture, this is without the distortion. So with the distortion I want to push to the left like that. On the right, I want to push to the right.

So the way to do that is the forward UV coordinates are negative on the left side of the screen, and positive on the right side of the screen. Okay, so how do we do that? Well we left off here, so this is going to be our displacement map, but I got to get positive on the right and negative on the left. So, we'll make a ramp, zero to one, use an add node to add minus .5.

Now my ramp goes from minus .5 to plus .5. So we take that negative ramp and our original motion UV map and we multiply them together. Now over on the right I've got positive code values and over here on the left you can see I've got all negative code values. So this side is going to push to the left, this side is going to push to the right. Pipe that into a copy node and stick the red channel into the forward UV right there, bing bang.

That goes into our eye distort node here. Use the forward channels, and now this amount of displacement will push to the right on the right hand side, to the left on the left and it'll taper to nothing in the middle, which is exactly what I want. You see that? In the middle, I get no displacement at all. All right, so that adds a little parallax to the illusion, okay? So we'll hook that up, hook this up, set this back.

I'll re-home the viewer. Okay, I'm going to set the viewer to bounce or ping pong as I like to say it, and we will now play, and now you can see we get the displacement in the bright foregrounds relative to the darker backgrounds. We have a variable density throughout the whole thing. We have dark areas with light areas and I've got slow movement on the ground level, faster movement up above the ground. So there you have it, fog, and a few techniques to make your fog a little better.

Be sure to check in next week, so you don't miss out on my next Nuke Nugget.