Shader Recipes: Rendering Realistic Tires in Maya

Introduction and Project Overview
In this short course, I'm going to take just a few minutes to talk about some of the things to keep in mind, as well as some workflows for creating realistic car tires. We can see we have really just a relatively simple scene that's been set up for us, it has a basic car tire in it. And you can see, that once I render this out, that this is really just completely flat. There's really no detail whatsoever, so, in a sense, we're almost going to start from scratch in this. Alright, the first thing I'm going to do is actually start to create the treads for this. Now, the treads can be created in a few different ways. You can either try to model this in, or, my personal preference, is to actually use something like a displacement map. To connect this, let's go into the tire material, and let's go ahead and just open this up in the Hypershade. If you take a look inside the source images folder, in the project we're working out of, you should see a file in here called, Tire Tread Displace, and that's what we're looking at right now. So you can see it's really just a simple black and white image, and it has the treads raised up on it. What I have done is, I've gone ahead and actually tapered these treads off so that they sort of fade into the side. What this should do, is whenever we apply the displacement, it should give me an area right here that just very gradually raises up from the side of the tire. Let's go ahead and connect this up. Let's jump over into the Maya Notes. Let's drop in just a 2D file. Here we are. Let's connect this up and if you take a look inside the source images, you should see the tire tread displace. There we are, we'll just middle click, connect this in as the displacement map, and let's render this out. You can see the displacement is definitely there now, but it's way, way too over pronounced. So let's come back, and we can actually start to bring this down by just going into the displacement file. And let's scroll down, take a look inside the color balance. We will make sure that the Alpha is Luminance check box is turned on, and now let's go into the Alpha Gain and start to drop this value way down, something like. 02 should be a pretty good starting point. And let's just see how it looks like in one little area. There we go, and you can see that it's now a lot more subtle than what we've had before. We can probably stand to bump this up just a little bit more, maybe something like. 04. In my case, right, that looks a little bit better. Let's go ahead and just render this entire image. Right, and there we go, so now really without just a whole lot of effort and a whole lot of headache, we can very quickly start to get these tire tread type patterns. You can go about this one of two ways, you can either use a displacement, which is what we've done here, or you could actually go in and model this type of detail into the tire itself. The reason I like to use a displacement is because I find it leaves us a much greater level of flexibility and freedom when it comes to actually being able to change this tire pattern, so if for whatever reason we needed to be able to change this tread pattern, we could easily go into Photoshop, make a few minor adjustments to this displacement map and be done and on our way, verses if this was actually modeled detail we would essentially have to go in and rebuild this tire all over again from scratch. Just kind of my personal preference as far as just, like I said, having a lot more freedom and a lot more flexibility to be able to make these types of changes. When it comes to actually building the tire material itself, this is actually sort of a tricky process, and one that's actually really, really dependent on your particular scene and the type of look that you're going for. Believe it or not, there's actually quite a bit of variation from one tire to the next depending on the manufacturer and the type of materials that go into that tire. It can have different colors, it can have diffferent levels of specularity and shininess, it can also have a really big impact on whether or not you have things like white wall or, rather, sidewall shine on your tire, that can affect the specularity a lot. You can also affect the specularity and the reflectivity as well as the color depending on things like how much dirt, how much grime you have on the tire, so it's really difficult to just have one set formula that's going to work for every kind of tire, but as far as a good starting point, kind of what I like to do is start with just a simple Maya blinn material, set it to something that is not 100% black, but just a really, really dark gray as we can see here. And then, as far as the specularity and reflectivity is concerned, I usually don't use any kind of reflectivity, but we use just a little bit of a kind of a low specular color so that it just overall gives it a really dull look. I find this to be a pretty good starting point, and then from here if I need to I can always go back and make some minor adjustments. Looking at our render, there is the main tire that we now have in place, or the main treads, but there's still quite a bit of detail missing, so what we need to do, is now start to introduce some of these details into the sidewall which, right now, we're missing. We could build these right into the displacement map, but what I prefer to do is actually build these into a separate bump map because that way I can now start to get a little bit finer detail and not have to worry about cranking my displacement up quite so high and to quite such a high approximation to get all the tiny little details in here. For this I usually just simply use a bump map. The bump map I'm going to be using in my case, what we have is really just a black texture right in this area, and then we have sort of this gray area right in here, so this is just small enough, or just different enough from this black background to start to raise some of these details up just a very, very slight amount. You can see I have things like patterns, some text in here, as well as a few little lines and streaks in here to just kind of help just add a little bit more visual separation. A lot of cars you see will have this type of detail in the actual sidewall, and essentially what we're trying to do is recreate these types of appearances that we would normally get- text, some different separating lines, a little bit of text here along the bottom, things like that. Let's go ahead and connect this in. Let's drop this in as just a simple file texture. We'll use this tire tread bump. Let's connect this as the bump map. Let's see what this does for us. You can see the bump is now in place, but in my case, it looks like it's a little bit too strong, and actually a little bit to soft and a little bit too spread out. What we can do to fix this, is let's start by going to the Bump Depth and let's drop this down quite a bit, something like from one to point one, we'll start with that. Let's also take this file texture that we're using here, and by default the File Type is going to be set to a quadratic filter, which means it's going to try to soften the pixels of this a little bit at render time. What we can try to do is, if we need to get this bump map sharpened up a little bit, is we can actually try to turn this filter off and see what that can do to help us. You can see now the bump is a lot less pronounced than what it was before, really kind of this subtlety is really what we're going for at this point. But, you will notice that, while it is relatively subtle now, at this point now it's almost completely disappeared into the sidewall of this tire. One of the things that we could probably do to address this, is to actually create what's called a specular map. By using this specular map, we can actually give different levels of shininess to different parts of this tire. What we can try to do is recreate some of the texture and effects that we would start to get in a real tire, where we have different areas that are a little bit more shiny, and a little bit more prone to specular highlights than some of these other areas. With a real tire this is actually created by these different tread patterns and things like that that are actually breaking up this specular highlight, but what we should be able to do is actually recreate this pretty effectively with just some simple black and white images. What I'll do in my case is drop in a specular map that has a really low level of shininess in areas like the tread, as well as some of these different sidewall panels, but these areas that are brighter should have now a little bit brighter specular highlight, and it should help these stand out a little bit more from some of the rest of the tire body. Let's jump back into the Hypershade. Let's connect it to the file texture, and let's drop in our tire tread specular map, and with this we can just drop this into the specular color. Just middle click, drop this in, and let's see what this does for us. You can see now that really does help a lot as far as being able to pull some of this detail back out, because now some of these areas that had the darker parts of that specular map have a little bit less of a specular shininess and a specular highlight, which means they really appear to be a little bit darker, so you can see what a difference that makes. One of the things you will notice now, is that while we have been able to bring out some of the details in these sidewalls, we've now lost a lot of this detail in the tire tread itself, because now due to the really, really dark specular color, we've actually lost a lot of that. In reality, this is probably closer to what we should see because these tire treads actually should not have a whole lot of specular shininess, especially due to the fact that this is the part that comes in contact with the road, and is going to have a lot of dirt, dust, and things like that on it. That's actually what we're missing right now, is the fact that this tire tread and these little tire tread grooves are, as far as the maps are concerned, they're the exact same color, which means there's really nothing to make these visually make these guys stand away. A lot of times what I like to do is use an additional diffuse map that sits on top of this that can have basically kind of a dirt map for things like the tire treads, and things like that, just to give it a kind of give it a little bit more visual separation from everything else. If we come back in to the Hypershade, let's go ahead and connect in this map that I have built called Tire Tread Diffuse. You can see it's really just another really, really dark gray material, or a dark gray texture overall, but right in these areas where the treads are, it's just a little bit lighter. What we should be able to do, is take this, just drop this into the color, and re render this. and re render this. There we go, and now you can see now how this gives this a lot more visual pop to these treads, compared to what we had before. And like I said, this really is what we should see because these areas of the tread that are actually coming in contact with the road and the ground surface. These actually probably should be a little bit lighter than just a flat black where we are going to be picking up dirt, dust, and things like that. In my case, it looks like the overall tire may be just a little bit too light, and now, for my particular scene, this is now being controlled by the diffuse texture. We could either take this back into Photoshop or we could even do a little bit of minor color adjustments here in Maya by just simply adjusting things like the Color Gain and the Color Offset here inside the Color Balance. If I start to bring this Color Gain down, what this is going to do is basically remap some of these darkest or, rather, the lightest areas and overall just kind of darken this up. I can try to bring this down just a little bit. There we go, that's a little bit better, gives us just a little bit darker result compared to what we had before. Right now, if we wanted to come in and maybe adjust the shininess and the actual specular highlight that we have here, we still have the freedom to do that. At the moment... let's just come in here and remap this. At the moment, we do have a map that's plugged in here, but this is only just controlling the specular color of this blinn material, we do still have control over the eccentricity and the specular roll off. What we could do is if we wanted to actually see this a little bit better, we could just temporarily disconnect this texture map and come in and make any adjustments to things like the eccentricity and the specular roll off. Maybe if we wanted this to be a little bit stronger and a little bit more focused as far as the highlight is concerned, we could make that adjustment, and that's pretty much now what the shiniest parts of this tire will look like now once we plug this map back in. We could now just take this, plug this map back into the specular color, because once that has been connected in, it actually becomes really, really difficult to make the adjustments to this eccentricity and the specular roll off, so that's why I kind of like to temporarily disconnect that. You can see now that we have a little bit more shininess and a little bit more of a specular highlight in some of these areas of this tire. Another reason why I actually like to use the displacement maps to create my tire treads is because it's actually a lot easier to re purpose that painted map in something like Photoshop to serve as something like your diffuse map, or your specular map, or whatever the case may be. If this were actually modeled geometry, that process becomes quite a bit more difficult, so, like I said, just for sake of ease and added flexibility I much prefer to use displacement maps as opposed to actually modeling this type of detail out. That's a look at how we can start to use a variety of maps and just a few additional tips and tricks that we can start to use whenever modeling and rendering tires of our own.