Learn how to improve sample quality of interior daylighting.
- [Instructor] The portal mode of an Arnold light improves the sampling quality of an Arnold sky dome. This is most useful when rendering interiors with natural light. As we saw in a previous movie, anything we put in the environment slot is automatically mapped to an Arnold sky dome. In this scene, I have an environment map providing backlight. That happens to be a bitmap, but it could just as easily be a flat color, or any spherical environment such as a 3DS max physical sky, or an Arnold physical sky.
Click render production to render the physical camera. To make it easy to see the quality improvement that a light portal provides, I've set the camera to expose for the interior, rather than the sky dome or back plate. Let's clone the rendered frame window so we can compare it later. We can now create our Arnold light. I'll enable 3D snaps, and I'm snapping to the grid points. Go to the Create panel.
Lights, from the pull down list choose Arnold. Click Arnold Light, and click and drag in the top viewport. Click to create the light, and then hold the mouse and drag out to create it's target, and release the mouse. Then right-click to exit the tool. I set it up so that the light is facing into the room. Let's look at that in the perspective view. I'll tumble around, Alt+middle-mouse. We want the light portal to be just outside the window.
Let's do that precisely. Select both the light and its target, using the move tool. Select and move. Click to select the line that joins the light and its target. And now, the move gizmo moves to the center, meaning we've selected the light and the target. We can turn 3D snaps off, and in the front viewport right-click, and then move the light upward. In the front viewport right-click again, and move forward closer to the window.
All right, then we can adjust its parameters. Go over to the modify panel, and just select the light, we don't want to select the target. We've got our target distance here, we can adjust that if we want. Let's see what that does. The target shows which direction the light is facing, and in perspective view, it's very clear that the light is facing into the room. All right, set that Target Distance to like a meter or so.
Scroll down, and set the Quad X and Quad Y to 1.3 meters each. 1.3 and then press Enter. Press Tab and enter 1.3, and press Enter again. And now, it's just a little bit larger than the available area of the open window. Let's look at that in the perspective view. Select that perspective view and press F3 to go into wire frame. Tumble around with Alt+middle mouse, move it around the scene.
Select the light. The Arnold quad light is just the right dimensions and position to channel the light coming from the sky dome, and improve it's render quality. Last thing we need to do to make that happen is turn on the Portal Parameter. We'll find that in the modify panel for the selected light. And down in the Shape section at the bottom, if the type is set to Quad you'll see Portal. Enable Portal.
And now, most of the parameters are grayed out. We're not able to set the intensity or color temperature any longer. It's just channeling the light coming from the sky dome. Let's do another production rendering, and compare it to the previous version. This draft quality rendering has been improved a bit with the addition of the portal. Let's compare it to the version without the portal. On the left, we have the portal, and you can see that the grain is much diminished, versus the version with no portal.
And we can zoom in on that. Hover the mouse near the flowers and use the mouse wheel. Zoom in a couple of times. Do that over here. Click in the window and then zoom in. And again, on the left we have the version with the portal. And in this case, we got an improvement in the overall exposure by increasing the number of samples that are directed into the room. So we can zoom back out. Come over here, and we can close this one, we don't need that any longer.
We can now bump this up to something closer to production quality by increasing the number of samples. Let's go into the render set up. And in the Arnold renderer tab, scroll down a bit. We've got the environment background and atmosphere section. Open that up, and in that section we have Sample Quality. We can increase the value up. Let's send it up to 8. And that's going to improve the direct light that's hitting surfaces in the scene.
This sample setting for the sky dome improves quality for surfaces that receive direct illumination, such as the tablecloth here. So we'll see less grain in that area. But the surfaces receiving bounce light, like this area back here, will not get a quality improvement from this Samples Quality setting. To also reduce grain in the global illumination, let's increase the sample value for the diffuse component globally. Let's go up to the top.
And we have the Diffuse samples here. We're going to turn that up to a moderately high value of 14. Note that we've got also a moderate number of bounces. We've got a Ray Depth of 5 for the Diffuse component. And I'm leaving the Camera anti-aliasing at a pretty low value of only 3. Let's go ahead and compare this. Make a clone of the current window, and then do a new render.
Increasing the samples of the sky dome and of the render settings has greatly increased the render time, but we've got better quality. Let's compare. On the left, we have a moderately high number of samples for the diffuse component of the rendering and also for the sky dome. And on the right, we have low samples, and it is, of course, much grainier. The one on the left is still a bit grainy, but we can make this better actually by simply rendering a larger frame.
Here's a full frame rendering of that same shot, with the same settings. The higher resolution of the rendering causes the effect of the grain to be diminished a little bit. That illustrates how to use portal mode to improve the quality of interior natural light, from an Arnold sky dome, and it ends the chapter on environmental lighting.
- Arnold rendering concepts
- Arnold lights such as quad, spot, and distant
- Modifying Arnold object properties
- Filtering light with the gobo filter modifier
- Image-based lighting with Skydome
- Daylight simulation with Physical Sky
- Arnold Standard Surface material parameters
- Diffuse, opacity, and bump mapping
- Rendering refractions with Transmission
- Building an Arnold shading network
- Test rendering with utility map
- Mesh subdivision and displacement at render time
- Atmospheric perspective with scene environment fog
- Rendering a spherical environment with VR Camera