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One of the big challenges that any artist faces when creating any kind of an interior render is the capturing of detail that oftentimes only gets highlighted or becomes noticeable in a render because of shadows in the scene. Now, rather than shadows created by light sources, what we're referring to here are really occlusion shadows, that is, a surface darkening that is caused by the close proximity of one object to another. This causes the general environment lighting to be somewhat obstructed or occluded, hence the name ambient occlusion.
We have of course already seen how difficult or at least time-consuming it can be to try and pull out small details in the scene using our global illumination engines, although certainly that is possible, especially if we use the Deterministic Monte Carlo engine. A somewhat quicker option that is available to us can be found in the Indirect Illumination rollout of our Options Editor, so let's go and open that up for ourselves. If we open the Indirect Illumination rollout, you can see we do have an Ambient Occlusion group.
By default, this option is disabled inside of the render engine, so if we want to use it, we would need to come and turn it on and then of course work with the Radius, Subdivs, and Amount controls to get the kind of effect that we wanted. This option is understandably very easy to work with and can add a nice bit of extra punch when it comes to pulling out details for our interior renders. The only problem with using this option is that our extra occlusion will now be baked into the final render. If we want to make any kind of a change to that effect, then we would have to re-render our entire scene.
This is why oftentimes artists prefer to work with an extra occlusion-only render, an extra pass that can be added over the top of a beauty render inside a post-production application such as Photoshop. Now, when using V-Ray in other applications such as 3ds Max or Maya, this is a pretty straightforward task. Then we have an extra text render element, or V-Ray Frame Buffer Channel, if we want to use V-Ray for SketchUp speak, that allows us to create custom element renders. This means we can use a V-Ray dirt map to create an ambient occlusion pass or element for ourselves.
The problem is V-Ray for SketchUp doesn't have such an option in its VRay Frame Buffer Channels list. In fact, if we just close our Indirect Illumination rollout, we can open up the VFB Channels rollout for ourselves and have a look. And as you can see, as we look down the list, we don't have a V-Ray dirt map or indeed an Ambient Occlusion channel that we can work with. Because this is so, we're going to take a slightly creative approach towards creating our own ambient occlusion element. Indeed, what we're going to do is use this Diffuse channel option.
Because this particular channel doesn't make use of scene lighting in its creation, it provides a very nice approach for creating an occlusion render pass for ourselves. Of course do keep in mind that we really are creating a workaround here, and so the workflow is a little bit clunky, but the end result that it produces is definitely very, very usable. So, the first thing we're going to do is go and create an ambient occlusion material for ourselves. So, let's open up our V-Ray Material Editor. I am just going to select the Scene Materials label, right-click, go to Create Material, and add a new standard material to the list.
Straightaway of course, I am going to go down to the bottom of the list where that new material has been added, right-click on it, and use the Rename Material function. And, as always, we're going to use a nice descriptive name; AO should work very nicely for us in this instance. Inside the Texture Editor, we can use the dropdown, and you can see we have this TexDirt node. This is essentially a V-Ray dirt map. Now, there are quite a few controls in here that we can work with; however, in this particular instance, we only need to make a change to a few of them.
The first change we'll make is to our Subdivs value. Again, this can be thought of as quality control regarding the noise inside our ambient occlusion effect. So, I am just going to set that to a value of 24. The next option we want to work with is our Radius value. If we want a nice subtle effect inside this particular scene, a value of 10 or slightly lower would work very nicely. But as this is a demonstration, I am just going to push this effect a little bit and make it very, very obvious for ourselves. I do want a little tweak to be made to our Falloff value.
I am going to set this to 0.5. Of course you can set it to a value that suits your particular taste. And then finally, I want to uncheck this Ignore for GI option. I have done this because we get a much smoother ambient occlusion result with our GI systems enabled. This of course means we need to uncheck Ignore for GI because we don't want this particular map to be ignored inside of those calculations. So with that final tweak made, we can now click OK. Naturally, we now need to apply our AO material to all of the geometry in the scene.
So, let's come up to the Edit menu. I am just going to choose the Select All command. And before I try and apply this material, I am just going to right-click on the geometry and use the Explode function. Do bear in mind, if you have nested groups in your scene, you may need to run the Explode command on them a couple of times. If you're wondering why we are exploding our geometry, this is just simply to make applying our material a one-click process. Having used the Explode command then, I just need to go and use the Select All function one more time.
Then we can just come to our Paint Bucket tool, click on our scene geometry, and as you can see, our AO material is applied to all of the geometry in the scene. Of course, we're still not ready to render just yet. We need to make certain that we have all of the channel elements that we need to work with. So again, I am just going to use spacebar to go back to my regular Select tool, and we're going to open up the Options Editor for ourselves. And inside the VFB Channels rollout, we can just click to select the options that we need. So we can enable our RGB color.
It will be rendered in there anyway. We can left-mouse-click to add an alpha channel, and of course we also want a Diffuse channel for ourselves. If you want to deselect any of these, then you just again left-mouse-click on them. Again, just to be certain, RGB Color, Alpha, and Diffuse are the channels that we need to work with. We do also need to point out that our image sampler controls are important. We need to make certain that we are getting a good level of quality out of them. This will affect our alpha channel and the ambient occlusion effect inside of our Diffuse channel.
So, I am just going to set our Type, our engine, to Adaptive DMC. I am going to make certain that we've got a reasonably high quality setting in here of 1 and 10. We should probably also point out that although we have our indirect illumination systems enabled, the actual settings we're using inside both the Irradiance Map and the Light Cache are very, very low indeed. We're not going to use the RGB Color channel from this render. We're not going to really get anything usable, so low-quality settings in there do not matter at all.
Well, now with those tweaks made, we are ready to go and enable a test render. So let's close our Options Editor and use the Start Render icon. Now, once our render is finished, clearly, as we said we would, we get nothing usable from our RGB Color channel. But if we just come to our VRay Frame Buffer Channels dropdown, you can see, first of all, we have our alpha channel. We're going to need this when we come to our compositing application. This will allow us to reclaim our environment background. And we also see that we have our diffuse channel, and if we click on that, you can see we get a very nice ambient occlusion render indeed, although, as you can see, our environment is rendering as black, which is why we need the alpha channel for use inside a compositing application.
As we said, this is a workaround and so it does leave a little bit of something to be desired in terms of its ease-of-use, but still, we can very quickly and very easily create a very nice ambient occlusion effect for ourselves that can be used to add a little bit of extra punch to our finished renders.
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