The Reflectance Channel, Part 15: The Layer Sampling Attributes

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Instructor Patrick Goski

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  • Duration: 17:43
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An overview of the layer sampling attributes and how they affect the quality of a render.

This video covers the various Layer Sampling attributes. These can be used to fine-tune how a specific reflection layer is rendered and include: Sampling Subdivision, Clamp Secondary, Cutoff, Exit Color, and Distance Dim. You’ll learn how the Distance Dim options can be used to fade a reflection based on distance, a popular effect in product visualization renders.



- In this video, we're going to take a look at the Layer Sampling attributes inside the Reflectance Channel. So we'll start by creating a new material, and rename this to "Owl Body", and then apply this to the Owl object in the Object Manager. We can then click on the Owl Body material again to bring up the attributes for the material in the Attributes Manager. We'll then click on the Default Specular and remove it. Then, we'll click Add and choose a basic Beckman reflectance layer. We can then click on the drop-down for Layer Sampling. This will reveal the various attributes that we can use to control how this reflectance layer will be rendered. The first attribute that we see here is the Sampling Subdivisions, and it's currently grayed out. The reason for this is currently we are using the physical renderer. And in this case, the sampling on the reflections is going to be controlled by the Sampling Subdivisions, the shading Min and Max Subdivisions, as well as the Blurriness Subdivisions. In some cases, you may be using the standard renderer, and when you're doing this, the Sampling Subdivisions inside the reflectance layer will become available. And this is going to be used to control the quality of the reflection when it's rendered. If we click on Render, we'll see that the reflected material is a little bit grainy in the bright areas, and this is actually due to the Anti-aliasing being set to Geometry Mode. But other than that, we're not really seeing anything too wrong with this reflection at the moment. If we start to increase the roughness of this reflectance layer and then render again, you'll start to notice that there is some heavy grain. This is because of the way that sampling is handled in the standard renderer. If we were to lower the Sampling Subdivisions and render again, the render will happen faster, but our rough reflection is going to be even grainier. So when you're working with a reflective layer that has a very high roughness, you also need to increase the Sampling Subdivisions when you're working with the standard renderer. This way, you can get a much smoother reflection. The trade-off here is going to be in the render speed. With that render complete, we can now see that we get a much smoother reflection. Here, we can see low samples, and the default samples, and then the high samples again. When you are working with the physical renderer, again, you don't have to worry about the setting the Sampling Subdivision inside of the actual reflectance layer. It should also be noted that when you're working with multiple layers inside the Reflectance Channel, you can set the Sampling Subdivision individually for each one of these when using the standard renderer. The next attribute that we have in the Layer Sampling is for Clamp Secondary, and this represents a brightness threshold. So we're using the physical renderer, and we're just going to click on Render to get a base render to look at here. Now, in this render, we're going to zoom in to the eye. Here, we can see that we have a very bright reflection on the side of the eye, as well as right here. This is reflection of the light or of the environment that's being reflected off the current material that we're working off with. So essentially, the first bounce in this scene is the reflection on the main surface, and then a secondary bounce is that light being reflected onto this other material. By lowering the secondary value or the Clamp Secondary Value, we can decrease the intensity of rays that are hitting this, and then moving on to another surface. So if we click Render again, you can now see that the reflection of the reflected environment on the main surface is less intense, as it has been clamped based on the value that we set. This is because the energy that's being bounced off of this surface is less intense now. So here we see a secondary value of eight, and now the reduced value or the Clamped Value. For the most part, you don't need to worry about adjusting this value too much and leaving it set to eight is fairly safe. In some scenes where you have a lot of secondary reflection bounces with very bright sources of illumination in the scene, it can be beneficial to reduce this. But again, it's not something you need to worry about too much. Going down to the next attribute, we have a cuttoff value, and this is going to represent the minimum brightness for a reflection before it stops being calculated. So in this case, we'll set the Specular Strength to zero and the roughness back to zero as well. We're then going to enable the Layer Fresnel. This will just be set to Dielectric. We can then go ahead and render. In the renderer, we can see that the entire object is still reflective, even though in some areas the reflection is fairly weak and we don't notice it that much. Like right here, we can still see a little bit of the backdrop in our sky. If we were to increase the cutoff value, you'll see in the preview that some areas that are not very reflective are not being calculated at all. If we click on Render now, we're going to notice that those areas that were very light in the reflection or not very reflective are cut off. So we're only seeing the contribution from the color channel, and then we're only seeing the areas that were more reflective. So here was the cutoff of 0.001 where we're still getting all of our reflections. And here, we have the higher cutoff value. In some cases, if you are using very dark colors and then low reflective values, such as an IOR of 1.07 with the default value, you may notice that some areas of the reflection get cut off with the low value. In these cases where you would need to have that reflection visible, you can decrease this value more. So if we set this to 0.0001 and then click Off, the actual Edit field shows zero. But the value that we set is still actually in there, so we're getting more of the reflections. For the most part though, the default value of 0.001 will work just fine. The next attribute that we have in the Layer Sampling is the Exit Color. First we're going to set the Fresnel back to zero, and we're going to leave the material just as it is, so 100% reflection. We're then going to go to the view and create a sphere. We'll just move this sphere off to the side so that it's sitting beside the Owl object, and we can move it up so that it's just about on the same level. We'll then apply the Owl Body material to the sphere as well. We can then click Render. In this render, if we take a look where the two objects meet, we can see that the reflection is going to bounce in between these two objects. But eventually, the reflection will just turn black and this is based on the number of bounces that are happening in the reflection. When the bounces stop or we run out of bounces, the Exit Color is going to be shown. So in this case, we just end up with a black spot on these two objects. If we go into the Render settings, we can go to Options and increase the reflection depth and render again. Here we can see with the reflection depth set high enough, the bounces happen 20 times and eventually fill up that black space. So here was a reflection depth of 5, and here was 20. The downside to increasing the reflection depth is that it can increase render times. So in this case, we can set the reflection depth back to five and render again, and we're going to notice that we get that black circle back. The Exit Color can be used to help fix this. So if we click on the Color Chip, we can choose something like red, and render again. Now, you'll see that rather than getting a black spot, we get a red spot. This doesn't exactly fix the issue, but it does illustrate what the Exit Color is doing. Is it simply defining a color that should be used when these reflection bounces terminate? If we were to set this to something similar to the actual color of our environment and then click on OK and render again, we get something that looks a little bit closer to what we would expect while still keeping the render times low. If we zoom out, it's definitely a lot less noticeable than a big, black circle. After the Exit Color, we have a checkbox for Separate Pass, and this can be used in conjunction with your multi-pass rendering. So in a case where you are working with multiple reflectance layers, you have the option of first off, setting the entire Reflectance Channel as a separate pass, but then each layer inside of the Reflectance Channel as its own pass as well. So we can set Layer 2 to a separate pass, and Layer 1 to a separate pass. We will need to have a little bit of blending between these, so let's go ahead and set a Fresnel on both. For Layer 2, we're going to add a little bit of roughness and decrease the Specular Strength. With the Separate Pass checkboxes set inside of the Reflectance Channel and the reflectance layers, we can then go to the render settings and enable a multi-pass rendering. If we click on the Reflection Pass, we have the option of choosing our separate materials. So we'll choose Selected. This is going to source the separate pass inside of the Reflectance Channel. We can then go to Separate Layers and choose All or Selected. If we choose Selected here, it's going to render out a separate pass for each each of the layers that we have separate pass selected for. These same options will be reflected inside of the specular pass. Now, if we render, we can then go to the Layer tab inside the Picture Viewer, and we see that we have the reflection Owl Body. If we expand this we'll see that we now have options for the Layer 2 that we have, which is slightly blurry, and Layer 1, which was sharp. The final set of options that we have in the Layer Sampling is for Distance Dim. So to show this off, we'll start by selecting the sphere and hitting Delete. Then, in the Picture Viewer, we're going to add in a plane and we can scale this up just so it's a bit larger. We'll then select the camera that we're using and make a copy. If we link to that camera, we can then delete the protection tag and move the camera back so that we see a bit more of the floor. We'll then create a new material, rename this to "Floor", and apply it to the plane. We'll then click on the material and remove the default specular and add a simple Beckman Shading Model and set the Specular Strength to zero. If we render now, we'll be able to see the results of that. You may have to click on Image to see the entire image. and then we can go back to the history. So here, you can see the owl and the environment reflected in the plane. In the Floor material, we'll enable Distance Dim. When you do this, you're going to get another preview added to the Layer Previews. This represents the fall-off curve for the Distance Dim. Now, if we render, we'll be able to see the results of the Distance Dim in action. So in this case, only rays that are within a certain distance of the surface are going to be reflected. If we click on the black arrow next to Distance Dim, we'll be able to get all of the attributes for this. If we increase the distance and click on Render, we'll be able to see more of the actual reflected object in the surface. We then have the Fall-Off slider. This is going to control the bias for this fall-off. Having this set to zero will be a linear fall-off. If we reduce the value, we'll see that the reflection is going to be very bright, close to the surface, and then fall off very gradually as we get further. In this case, we can increase the distance further to see this a little bit more clearly. If we set the fall-off in the other direction, it means that the reflection will stay very strong along the actual distance, and then cut off abruptly. So we can render again to see what that looks like. So right here, you can start to see the effects of the Distance Dim, although the distance itself is too high. So we can lower that, and then click on Render again. We can now see that cutoff more clearly. Again, setting this slider to zero is going to provide a linear blend. The final attribute that you have in the Distance Dim is the Distant Color, and this is similar to the Exit Color. When we were not using the Distance Dim, you would see that the environment itself is properly reflected. But as soon as we enabled it, the environment that should've been reflected is displaying the Distant Color instead. This is going to be the color that's used when no reflections are present. If we change the Distant Color to something like white and then click on Render, you'll see that you still get the reflections. But wherever a reflection is not present, white is displayed instead. So just to recap, in this video we covered the Sampling Subdivisions. These are used to control the quality of your reflection when you're using the standard renderer. So here we can see the Default Sampling Subdivision, Low Subdivision Sampling settings, and High Subdivision Samplings. The tradeoff here is going to be the render time. When you're using the physical renderer, you don't have to worry about setting the Sampling Subdivision in your reflection layer, as all of the settings will be controlled by the physical renderer itself. We then went over Clamp Secondary, and this is going to allow you to control the strength of secondary bounces from a reflective surface. So here, we can see Clamp Secondary set to the default value of eight. And we see the effect on the eye where the bounces coming off of the surface that we're dealing with are very bright. Lowering the Clamp Secondary is going to lower the intensity of these bounced rays. We then had the cutoff, and the cutoff is going to control when a reflection will be calculated and when it won't. So if the cutoff value is too high, then light reflections will not be calculated. So here we can see the default cutoff value, and then a high cutoff value where reflections are no longer being calculated. The Exit Color allows you to control the color that will be used when the maximum number of reflection bounces happens. So here, we see the default color of black using five bounces. We then increased the bounces to see what it should look like. The red color was set as the Exit Color just to highlight what's happening here, and then finally the Exit Color was set to a gray color, something that's closer to what this material might actually terminate at. We then covered Separate Passes, which is going to allow you to split off each reflection layer into its own pass when using multi-pass rendering. Finally, we covered the Distance Dim options, which allow you to control the distance from the reflective surface that these rays will actually be calculated. So here, we see no Distance Dim, and then the defaults, which cut off any of the reflections based on the distance. You then have sliders to control the overall distance, the fall-off curve for the actual reflection, and a Distant Color, which is going to allow you to set the Exit Color for these reflections when using Distance Dim.
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