The Reflectance Channel, Part 14: The Fresnel Attributes

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Instructor Patrick Goski

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An overview of the Fresnel attributes.

In this video you will learn about the various attributes to control the Fresnel effect of a reflection layer. You’ll learn about the Dielectric and Conductor modes, when and why you would want to use either. You’ll explore the presets associated with both, and how the Strength and IOR sliders affect the Fresnel. You’ll also learn how the Fresnel properties compare to the Fresnel shader applied within a Layer Mask.



- In this video, we're going to take a look at the Fresnel attributes inside a reflectance layer. So the first thing that we'll do is create a new material and rename this to "Owl Body". We'll then apply this material to the Owl Body in the Object Manager, and then click on the Owl Body material again to bring up the material attributes. We're then going to set the color to something a little bit darker so that we can see the properties of the reflection on the material better. Next, we'll go to the Reflectance Channel, and then select the Default Specular, and remove it. We'll then go to the Add button and choose a Beckman shading model. We can then set the Specular Strength to 0%, as we don't want to have any contribution from the specular. If we scroll down, we'll see that we have the Layer Fresnel options available to us. The Fresnel effect is going to control the strength of the reflection based on the angle of the surface to the camera. So with the Fresnel set to None, let's go ahead and click Render. With the render complete, you can see that the object is a perfect mirror surface, and the strength of the reflection across that surface doesn't vary. Going back to the Layer Fresnel attributes, we can start with the Fresnel drop-down. This let's us select between None, which gives us the result that we see, Dielectric, or Conductor. Dielectrics are going to be materials that do not conduct electricity well. This includes things like glass, plastic, and water. Conductors are going to represent metals, and these are good conductors of electricity. Depending on the option that you choose, you'll get different presets available to select. So if we start with Dielectric, the preset starts at Custom, with an IOR, or Index of Refraction, of 1.35. If we then click Render, we're going to see that the areas of the object that are facing towards the camera are less reflective, and the surfaces that are facing away from the camera are more reflective, and this is controlled by the Index of Refraction. A setting of one will produce no reflections at all, and by increasing the Index of Refraction, you can get stronger reflections, although there will still be areas where the color channel is still showing through. Next you have presets, and these presets are simply going to select a specific Index of Refraction for that specific material. So for something like Asphalt, you can see that it changes the IOR to 1.635. If we set this to Glass, we get 1.517, and something like Water gives us 1.33. We then have a strength slider for the Fresnel effect. So with a setting of 100%, you're going to get the exact representation of what this is going to look like using that Index of Refraction. By lowering the strength, you're going to reduce the amount of contribution that the reflectance layer will receive from the Fresnel effect. So with a strength of 50%, we're going to see that the object is mostly reflective across the entire surface. But then, some areas are still going to receive a little bit of the Fresnel effect. With a strength of 0%, we're going to see that we get a 100% mirror-like surface. With both of these sliders, you have the option of adding in a texture. This could either be a bitmap or a shader to modulate the effect of the slider across the surface. So if we set the strength to 100% and then add in something like a noise shader, and just adjust the contrast on that so that we have an area of greater contrast and render, you'll see that the areas that are black are going to represent zero strength, and this provides us with a mirror-like surface, with no variation in the strength of the reflection. Areas that are white are going to represent a 100% strength, and this allows us to see the full effect of this Fresnel coming through. So here, we can see a white area where the surface facing the camera is partially reflective. And as we go to an outer edge, we'll see more of the Fresnel effect in these white areas. Similarly, we can do the same thing with the Index of Refraction. So, we can twirl down the triangle there to bring up the shader slot, and we can add in a noise. With the noise added, it's going to modulate between white being the value that we set in the slider, and black representing one. So if we increase this to something stronger like 2.35, and render, you'll be able to see that some areas have a higher Fresnel value, or Index of Refraction, and other areas have a lower Index of Refraction, which gives the apparent result of lighter reflections and more of the color channel coming through. The next thing that we'll take a look at is going to be a conductor. So the first thing we'll do is clear out the shader from the Index of Refraction. We can then set the Fresnel drop-down to Conductor. This provides us with one new slider, which is the absorption. But first, let's take a look at the presets. When using the presets with a conductor, you're going to be using a data set that is scientifically collected. This means that the wavelength will change based on the surface angle, which can provide color shifts inside of the actual Fresnel effect. A good one to describe this is Tin Telluride. When we select a preset, you'll notice that you can no longer set a custom IOR or absorption. That's because these values are specified by the data set that was collected for this specific material. We can then click on Render to see the results. With the render complete, you can see that we get a shift in the shading across the surface. The outer edges are going to appear more white, while areas facing the camera start to get more orange or red. But we can also see that the color channel is coming through. This is one thing you have to watch out for when creating metallic surfaces. As generally, when working with conductors, you don't want any contribution from the color channel. So we'll go to the Basic tab and disable the Color Channel and then render. With this render complete, you're seeing a proper representation of the Conductor Fresnel. We can then go back to the Reflectance Channel and choose a different preset, like Gold, and click Render. You'll see that the Fresnel is actually adjusting the color based on the preset. Again, this is because of that scientific data set that has been collected from these specific material types. If we set the preset back to Custom, we'll get these sliders back again. In here, we can set a custom IOR value to control the strength of the Fresnel effect, and we can also change the absorption. So with an IOR for the conductor of 2.81, we can click on Render, and we'll see that this gives us a fairly strong reflection. But if we adjust the absorption, we can control the overall brightness of this reflection. So if we reduce the absorption and click on Render, we're going to see reflections that are darker. Increasing the absorption will increase the overall brightness of that reflection. Like all the other sliders that we have, we can twirl down the Absorption attribute to get a length field for a texture. Again, this can be a bitmap or a shader, and this will control the absorption value based on the slider that you've set. White values inside of the shader will represent the full amount of absorption that you set, and black values will represent zero. The next option that we have is a checkbox to invert the effect of the Fresnel effect. We're going to start by going to the Basic tab and re-enabling the Color Channel. We'll then go back to the reflectants and set the Fresnel to Dielectric. If we render using the IOR of 2.35, we're going to see that we get a fairly reflective material, but we still see the same sort of properties. Areas that are facing the camera are going to be less reflective, and areas that are facing away from the camera will be more reflective. If we click on Invert, it will invert those reflective properties. So if we render now, the areas that are facing the camera are going to be more reflective, and areas facing away from the camera will be less reflective. The next checkbox that we have is for Opaque. So we'll start by turning off the Invert checkbox. We'll also want to add a new layer. So we'll go ahead and add another Beckman Shading Model, and set the specular down to zero. We can call this "Top" and then "Bottom". The bottom layer is going to be set to None, so it's not getting any sort of contribution from the Fresnel attributes. We can then go to the Layer Mask and set the color to something like red. We can change the attenuation model for this to Maximum so that we're getting the full red reflection. We'll temporarily disable the top reflection layer and render so that we can see just the red reflection. Now, if we go back to the top and enable it, we'll see that the Layer Fresnel for this is set to None, and if we render, we'll notice that it's going to completely override the reflectance layer below it. We can then add a Fresnel type. So we'll choose something like Conductor, and then render again. With the conductor set, we are getting a metallic reflection. But because it's not 100% reflective, we can see through to the red layer below. The Opaque option is going to make it so that this specific layer is going to blend directly with the color channel. So if we click on Opaque and then render again, you'll see that rather than seeing red below this specific reflection layer, we're going to see the color channel instead. This means that if we were using something like a Layer Mask and adding in a noise and just adjusting the contrast so that that has a clear definition between the white and black areas, and render, what we're going to see is areas that are 100% red, or represent the bottom reflectance layer. And then areas that are white are going to be receiving the Layer Fresnel effect. But because we're using Opaque, it's blending with the color channel below, rather than the reflectance layer below. If we uncheck Opaque and render, you'll see that you just get a blend of the top reflectance layer over the bottom reflectance layer. The final thing here is the difference between the Layer Fresnel and the Fresnel shader. The Layer Fresnel is going to be useful when you need to create physically accurate Fresnel effects. If you want to create a Fresnel effect that still has more artistic control, then it's still good to use the actual Fresnel shader inside of the Layer Mask. This way, you can go into the Fresnel shader and adjust the gradient to suit. You can still use the physical checkbox. But in this case, all you're doing is replicating the exact same functionality that you'll find with the Layer Fresnel attributes. So just to recap, in this video we covered the Layer Fresnel attributes. This includes using the Fresnel drop-down to select between No Fresnel Effect, Dielectric Materials, or Conductor Materials. Dielectric represent things that are not good conductors of electricity, such as glass, plastics, or water. Conductors represent metal surfaces, or things that are good conductors of electricity. This Fresnel type will be based off of sampled materials from real life, using data sets that produce the correct coloration based on the camera angles and the presets selected. We then have presets, and these are going to allow you to choose between Conductor presets or Dielectric presets.You then have the strength, which is going to control the contribution of the Fresnel effect with 100% being the Fresnel effect as it should be and 0% being no Fresnel effect at all. The Index of Refraction controls how the fall-off happens based on the camera angle. And then with the conductors we covered the absorption, which controls the overall brightness when using the Custom preset. We went over the Invert checkbox, which is going to invert the effects of the Fresnel effect in the render, and then Opaque ,which is going to control blending between the actual layers in the layer stack for the Reflectance Channel or allow a specific layer to blend with the color channel and overwrite anything else inside of the layer stack. Finally, you still have the option of using the Fresnel shader inside the Layer Mask attributes to have artistic control over a Fresnel effect. But in cases where you just need something that's physically accurate, you'll want to stick with using the Layer Fresnel attributes.
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