Advanced multi-channel texturing

"Advanced multi-channel texturing" by Ziv Qual
I’m not gonna go through all the specific parameters of each map because many different combinations can work just fine and it is all a meter of trial and adjustments, you can look at the shading network chart I’ve made to get the idea. My advice for this step is to add one map at a time, and always make sure you keep track of the contribution each map gives to the details. It sometimes helps to copy the specific map you are working on to a clean new material and apply it to the model just to check how it fits it.
tip – I often use an Ambient occlusion map as a mix map at the base of the diffuse color for added depth detail – for the white color I simply add the maps I was gonna use anyway and for the dark color I add some noise maps for "corner dirt".
Adding a mix level procedure and a few material editor notes
Before we go further, I just wanna share a few insights about the material editor and explain the process of adding more and more details to an existing map generally – these things will be most relevant for the next step.
– General idea of the process of adding another mix level
So we have a nice base shader by now but we wanna start adding more specific details to maps we already have in the diffuse color / bump / glossiness / reflection color, how can this be done ?
The answer is to add another mix level to these maps and then add another mix level and another – there is no limit to this except the more levels we add the more complicated it will get, this is why it should be done in an orderly fashion and this is how it should be done:
1) Go to where the map you want to add a mix level to is located, right-click and CUT that map. for example – if the map is in the diffuse color slot then we go to the diffuse color map slot in the base material. another example – if the map is inside a mix, we go to that mix.
2) Add a new mix map where your map was, right click on the map1 slot and paste your original map back. after this step your material should act the same as it did before, you’ve simply prepared your map for additional details.
3) add a black and white bitmap in the mask slot and name the mix map accordingly to the mask. for example – if you added a "blood stains" bitmap you should name the mix map blood stains. naming your mix levels will help you later on when the material starts to get complex. The black pixels of your mask represent where your original map will be and the white pixels represent the new color2 / map2.
4) adjust color2 / add a new map to map2 slot of the mix. for example – blood: in the diffuse color you might wanna add a red noise map there, in the reflection color you might wanna add that same noise map but with a darker shade of red since the blood is dry and less reflective than the armor’s metal,in the bump map you might wanna use that same noise map but with bright grayscale colors since the blood stains act as OUTER dents.
5) go to the mask and give it a new map channel. This is the last step in the material editor. since you’re going to use several different masks you’re going to need to use different map channels in order to create different UV’s to map each mask separately. I’ll explain a bit further about map channels next.  
– map channel (material and uv map / unwrap)
What are map channels ?
Usually, when we add a texture and the modifiers UVWmap / Unwrap they come at the default of map channel 1. But an object can have more than one UV, you can add more than one of these modifiers and when set on different channels they do not override each other. All you have to do is keep track of which map channel each texture is using and which modifier is set to that channel.
– output benefits Back to the material editor. Since we covered most of the process in the material editor, In the next step I’m going to focus mostly about how to work with the UV’s but I would like to first share how I go about doing most of the tweakings once I’ve already added some mix levels.
I’ve noticed that not many people are aware of how useful the "output" tab is. Through the output tab you can easily override and adjust the weight each and every map gets in the mix levels. It allows you to manipulate the colors and sometimes "override" the limit of the contribution a map gives.
I will go quickly through the parameters:

Output amount – gives control to override the amount of contribution the map will have to the material.
RGB offset – this basically controls the darker colors of the map. I often give this parameter values below 0 to strengthen the contribution of the darker colors to the material.
RGB level – this basically controls the brighter colors of the map. I often play with both RGB level and RGB offset – these 2 parameters can balance each other and the further they are from each other the more "overridden contrast" the map gets.
Bump amount – this parameter is very useful to tweak the contribution to the bump for each map. it has effect only in the bump slot, obviously
Enable color map – this one gives a bit further control to most of the things mentioned before but here you can manipulate the map itself and it’s colors. it is very useful when you want to use the same bitmap but with some variations – it eliminates the need to create new bitmaps just for that or going to photoshop just for some basic color adjustments.
– Working with the limits of "show map in viewport"
One last material editor note before we move on. Max is very limited in it’s ability to show how the maps sit on the model in the viewport – it often doesn’t show the correct scale of procedural maps and when several maps are mixed together it can’t show the combined end result in the viewport. That is why for the next step you will always need to go to the specific mask you are setting the UVs for and turn "show in viewport" from there. In any case, doing a test render every now and then to see how everything combines on the model is a must to progress correctly. 

STEP2 – Mixing in details in different map channels and adjusting them on the mesh
Everything done so far can be considered as preparation for this step, this is the main step for this technique. I’ve explained how I go about adding more mix levels to the material editor so now I’m gonna focus on what I’ve done with the uv’s for each mix level I’ve added.
map channel 1 – blood and general maps
Map channel1 is the default channel that comes when you work with objects and textures. That is why I didn’t really need to make a new map channel for it – just moving around existing uv’s to set where the blood stains fall was enough. I didn’t even need to unwrap any model because even if inevitable stretches and overlaps occurred – it didn’t really meter too much. There is a meaning to the order of the mix levels and since the blood will cover the rest of the details, it goes to the base of the maps.
Map channel 2 – Side decorations / diamonds’ gradient
This is where this technique really takes advantage of it’s potential. When preparing the mask, I had to make sure that it can be seamlessly tileable horizontally and that I have enough "empty black space" to work with the uv’s. I went through every armor part and added an Unwrap modifier and set it’s channel to 2. First step is to scale down all the uv’s to a really small chunk and put them on the side on an "empty black space", then select a few polygons on the side of the model through the unwrap, hit planner mapping and organize the uv’s while seeing in the viewport how the side decorations fit the model. This process is repeated with every few polygon chunks from the corners of the model and then I weld them all into 1 long "uv line". The great thing about doing it this way is that I can really easily manipulate the side decorations to grow or shrink with the model’s flow and get the feedback in the viewport in real time.
In this tutorial I am focusing on the shading of the armor’s metal material but I just wanted to mention here that I’ve also used the same map channel 2 unwrap for the diamonds – in the diamonds’ material I’ve placed a radial gradient map in the "extra light" slot to give them extra subtle depth, I went through every object that had diamonds in it and in the same map channel 2 unwrap modifier that was already there I’ve selected the diamonds uv’s and manipulated them around one of the tiles of the gradient (and not necessarily in the center of the uv’s to avoid cluttering).
Map channel 3 – Symbols
Again, When preparing this mask, I made sure I kept enough "black empty space" between the symbols, That is also why for this map I turned tiling off – to have more empty space to work with on the corners. So now we go again through every armor part, add another unwrap modifier and set it to channel3. First step is to select all the uv’s, scale them down and take them outside of the uv box (which should be enough to "make a clean start" since the tiling is turned off). The idea now is to select the polygons that will have a symbol, hit planner and and manipulate the uv’s until you are happy with how the symbol sit’s on the model. Again, immediate viewport feedback makes it possible to nicely "deform" the original shape of your symbol to fit the shape of your models more "naturally", this also helps avoiding having a cloned look when using the same shape several times. (take a look for example at how much the big shape on the helmet is deformed from its original texture to fit the flow of the helmet).

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