The Reflectance Channel, Part 08: Layer Blending

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Instructor Patrick Goski

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  • Duration: 07:43
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An overview of Layer blending within the Layers tab of the Reflectance channel.

In this video you will learn about the Layer Blending dropdown found in the Layers Tab or the Reflectance Channel. These options include Normal blending and Add Blending and affect how the various Reflectance layers blend together.



- In this video, we're going to take a look at blending reflectance layers within the Reflectance Channel. So we're going to start by creating a new material and calling this "Owl Body." We'll then apply this to the Owl Body object in the Object Manager, and click on the Owl Body material to see the attributes for the Reflectance Channel. Because we only want to see the contribution from the reflectance, we're also going to go to the Basic tab and turn off the color. We can then go back to the Reflectance tab to start working. For the purposes of this video, we're just going to take a look at how we would blend multiple reflectance passes together, rather than the specular at first. So we'll click on the Default Specular, and then choose Remove. We can then click on Add and we'll just use a basic Beckman Reflectance Model. When we add this, it'll be set as Layer 1 with a blending mode of Normal. We'll also want to go down to the Specular Strength and set this to 0%, so there's no chance of contribution of the Specular Strength to this reflectance layer. Next, we'll click on Render to see the results we're getting. So here we see the owl model with a 100% reflection of the environment around it. Now, if we want to see how the blending works between these layers, we need to have more than one reflectance layer inside the Reflectance Channel. So we'll copy this layer and paste it on top. If we render again, we'll see that there's no change in the actual reflectance value for the scene. The reason there is no change is because Layer 2 is currently set to the Normal Mode, and in this case it's overriding 100% of whatever is underneath it. If we try changing the slider value for the layer mask and render again, we're also not going to notice any change. This is because the layer underneath matches the layer that is on top 100%. So what happens now if we change the blending mode for the layer on top? If we set this to Add, you'll see that the reflection in the material preview gets brighter, and if we render we're going to see the same thing reflected in the actual Render. In this case, it's adding these two layers together. So the reflectance from Layer 1 is our base amount, and then the reflectance for Layer 2 is the exact same. But because we are adding this on top of the other one, it's essentially doubling all of the reflection values in the final Render. In this case, you really want to watch out for what values you're working with if you are changing the blending mode this way. Let's take a look at another example of how this blending can work. So we'll just hide the two layers that we currently have so that we have absolutely nothing from the Reflectance Channel that is going to be acting on this. We'll then click on Add and choose Beckman again, and set the Specular Strength to 0%. If we go to the Layer Mask, we can now set the color from white to 100% red, and then click OK. If we render, we'll see that we're going to see a red reflection and even the areas that used to be pure white will now be red. Let's go ahead and rename this layer to "Red," just so that we have an easy indication of which color we're using. We can then copy this channel and paste it. The new layer will be called "Green," and then in the Layer Mask we'll go ahead and set the color from red to 100% green and click OK. We can see in the reflection preview, we're getting a green reflection. But in the material, we're getting a blend between the green and the red. This is going to be slightly yellow as we would expect if we had 100% green and 100% red added together. But it's still leaning more or less towards the green value. This is because when we are using the normal blending as well as a color in the Layer Mask, we're going to get a partial contribution of whatever is underneath. That is just because of the way that it's reading these values and allowing us to see through this. If we take the green and set that to Add Mode, you'll see that we get a proper yellow reflection. This is because in those areas where we have 100% green and 100% red, they're now added together properly to give us a 100% yellow. Let's continue with our stack. So we'll copy the green channel and paste it. You'll see that this is already set to Add Mode as the green layer was. But this time, we're going to rename this to "Blue," and then go to the Layer Mask and set this to blue. In the reflection preview, we can see the blue reflection. But then in the material preview, we're seeing a 100% white reflection. If we render, we'll see that this is going to match the original reflection that we had created. So in these areas where you would have a partial contribution, so we can see the 100% blue, the 100% green, and the 100% red, when we add these together we're going to get white. If we set the blue to Normal Blending Mode, it's going to have that same blue cast to the actual reflection. Again, that's because the blue values here are not providing a 100% reflection, and some of the layers underneath will be seen through that blue layer. Now, this does allow for some interesting effect. If we set the blue channel back to Add, so we're getting that 100% reflection again, we can start adding some roughness between these three different layers. So let's actually leave the blue layer set to a roughness of 0%. Then we can go to the green and add a little bit of roughness. This is going to spread out the green reflection from the blue reflection and the red. You can see in the material preview, we actually get a green fringe around those areas that are a 100% white highlight. If we render that in the picture viewer, you'll start to see that clearly. If we then go to the red channel and increase the brightness over top of the green, we can now get the effect of a film where the color is actually going to shift based on the roughness of these three channels together. If we set these all back to Normal Mode, we're still just going to get that blue cast on top of everything. But we will see a little bit of the contribution that is happening when each of these layers has a varying roughness.
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