The Reflectance Channel, Part 09: Using the Roughness attribute with a Reflection

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Instructor Patrick Goski

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An overview of the Roughness attribute in conjunction with a Reflection

In this video you will be introduced to the Roughness attribute and how it will affect the glossiness of a reflection. Adding Roughness is the key to create blurry reflections. You’ll also learn how to control the roughness using a texture.



- In this video, we're going to take a look at the Roughness attribute inside of the Reflectance layers. So the first thing that we'll do is create a new material and call this "Owl Body," and then apply that to the Owl Object in the Object Manager. If we then click on the material, we'll be able to check out the properties for the Reflectance channel. Now, we're going to start by deleting the Default Specular, and then adding Beckman from the drop-down. Once we've added the new Reflectance layer, we can see two previews just below. We have a preview for the actual reflection that's going to be contributed from this Reflectance layer, as well as a graph representing the falloff. At the moment, this graph is not showing anything, and if we click on Render we'll see that the results that we get are a perfect mirror surface. In this case, we can adjust the roughness to adjust how glossy this surface appears. So if we increase the roughness, you'll see that the graph on the right-hand side changes. We have one section on the left that represents the falloff for the reflection, and then on the right we see the falloff for the specular. If we adjust the specular strength, you'll see that this adjusts the height of this curve on the graph and the same thing goes for the reflection. In this case, we're just going to take a look at how this affects the reflection. So by increasing the roughness, we now see a result on the graph and we can see that the preview is showing a fairly rough surface. If we click Render, we're going to see that reflected in the final render. So in this case, if we go back to the glossy version we can see that all of the bright areas have clear, defined lines where the objects were in the environment. When we increase the roughness, these bright spots are going to spread out across the surface and all blur together. If we go to the Type drop-down, we can select between Beckman, GGX, Phong, and Ward. When the roughness is set to zero, you're not really going to notice any difference between these four reflection models. But as you increase the roughness, you'll start to notice that the graph changes. With Ward, you get a very sharp reflection. As you increase the roughness eventually the curve is going to come back in on itself, meaning that you'll get areas that are more blurry and then sharp, and then blurry again. Changing this to Phong, you'll see that the reflection eventually just becomes perfectly even, so it has the same roughness all the way across the surface. Changing the Roughness slider is going to allow you to see how that graph changes based on the roughness. We can then select GGX, and you'll see the results again. Finally, back to Beckman. In this case, you can see that it dips in on itself again. When using the reflection strength and the roughness, you're generally not going to notice a very large difference between how this looks between the four models when you're doing your final renders. So really, it's going to be choosing the model that looks the best to your eye. Next, when using the roughness, you have the option of adding in a texture, and this texture can be used to modulate the roughness across the surface based on a shader or a bitmap. So if we click on the Texture menu, we can add something like a noise. You'll see here that the reflection preview now looks like it is spotty. This is because the roughness is modulating between 100% and 0% based on this image. In this case, white areas of the image are going to be 100% rough and black areas will be 0% rough, or glossy. If we click Render, we'll be able to see what that looks like. So if we zoom in on the image, you'll be able to see that the reflection is becoming more blurry in areas that are white, and sharper in areas that start moving towards black. If we go into the noise and increase the contrast of this image, we'll be able to see something that's a little bit more defined in the final render. That's because we'll have areas that are 100% blurry and others that are perfectly glossy. The next thing to know when dealing with this is that this texture is going to modulate between the actual roughness set by the slider. So if we set the slider to 50%, it means that the black is still going to be 0% roughness, but now the white areas are only going to represent 50% roughness. If we click Render, we can see that these areas will be a little less rough. So here it was with 100%, and you'll see that the bright areas really get spread across the surface, and with 50% there is less of that spread happening in the reflection. So just to recap, we went over the Roughness slider when using a reflection, and this is used to control the glossiness of the material. We can see the preview for the material in the left-hand preview here, and then a graph representing the actual falloff curve for that reflection. We can then add in a texture, either a bitmap or a shader, to control or modulate this roughness across the surface. Remember, white is 100% rough and black will be 0%.
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