The Reflectance Channel, Part 10: Using the Roughness attribute with a Specular

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Instructor Patrick Goski

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An overview of the roughness attribute in conjunction with a Specular Highlight.

In this video you will be introduced to the Roughness attribute and how it will affect the glossiness or width of a Specular. You’ll learn about the need for roughness when using either the Beckman, GGX, Ward, or Phong shading models, as well how the roughness can be controlled using a texture.



- In this video we're going to take a look at how the roughness attribute affects a specular highlight. So start by creating a new material and call this "Owl Body" and apply this to the Owl Body in the object manager. We can then click on the material again and take a look at the properties for the reflectance channel. In this case, the default specular is set on the object. So we'll click on this and hit Delete. We can then render in the view port to see what we're working with at first. Next, we're going to click on add and choose Beckman. By default this will come in set up for a reflection. And if we click Render, we're going to see the environment around the owl reflected. But this isn't what we want. We only want to see the highlight that should be dictated by the actual lights in the scene. So start by setting the reflection strength to 0% and increase the specular strength. Next, because we are working with a specular, we need to set the attenuation from average to additive. At this point we can see the color channel showing through. Let's go to the color channel as well and just reduce the brightness of this material so we can see the specular better. If we click on Render, you'll see that the result that we get is a fairly flat, blue color. So when dealing with the specular strength and using any of the main four shading models, you also need to add in roughness. The other thing that you'll need to do to have any sort of contribution from the specular is make sure that you have lights in your scene that are contributing to that specular. Since we already have the lights, we can go ahead and add some roughness. As we increase the roughness value, you'll see the specular highlight in the preview and on the material. If we click Render, we're going to see the results of the specular on the object now. If we zoom in, you'll see that the specular comes up as a group of small points, and this is because we are using area lights to cast this specular. When using an area light, you're essentially getting a grouping of individual point lights. So when the specular is not wide enough, you're seeing each one of those individual lights. As we increase the roughness and render again, you'll see that eventually these all blend together to look like a nice, smooth specular for our object. As you increase the width, it's going to change how the specular looks and how far across your object that specular spreads. When we were using the reflection, changing the roughness didn't really change the rendered results too much. But if we switch between the different models now, you'll see a fairly significant change between how that is going to effect the shading. So when using something like GGX with a very wide roughness or a wide fall-off curve, you get a fairly sharp point that can give you nice, bright highlights, but then it falls off very smoothly. If we take a look at Beckman, which had a sharper curve, you'll see that it's blown out quite quickly, and the fall-off along the surface is rather sharp. Switching between the different models is going to allow you to see the results that you get between those. So when using any of the four shading models here, the roughness is essentially going to control the width of your specular. Just like with reflections, you have the option of using a texture to modulate this roughness. So we can open up the Texture menu and add something like a noise. And you'll see that that is going to create a spotted effect for the specular., and this is essentially because some areas are rough and will spread the light across, and others are very glossy, which means the light isn't really going to spread at all. So just to recap, in this video, we added a Beckman reflectance layer and we set he reflection strength to 0 and the specular strength to 100%. We then set the attenuation to additive so that it blends with the color channel. The roughness was then used to control the width of the specular highlight. And just like with reflections, we used a texture to modulate the actual roughness across the surface.
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