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In this video, we're going to be working with our same interior scene to create another global lighting solution, this time using V-Ray's Light Cache system set as our primary engine. We're going to follow the same procedure as with our irradiance mapping exercise. Let's see what kind of solution we can create using the basic Light Cache controls. So with our Ch03_GI scene file loaded, let's once again go and enable V-Ray's GI systems. To do that we need to open up the Options Editor, come down into Indirect Illumination rollout, and again put a check in the On box.
Then of course, we need to go and setup our Engine Type, so let's scroll down. Let's set Light Cache as our Primary Engine and as before, we need to disable our Secondary Engine. And if we just scroll down, you can see that the system gives us some default settings so that we're literally ready to render with Light Cache. The problem with these default settings is that they really are assuming that we're using Light Cache as a secondary bounce engine, which really is its recommended role, and we'll mention that a couple of times throughout this video.
If we just dismiss our Options Editor though, we can take a test render for ourselves, and we should see a couple of things straightaway. Firstly, we notice that with those default settings, once the Light Cache calculation actually starts, it create a GI solution very, very quickly. We should also notice in the final render that we do get a lot of light bouncing around our environment. In fact, we're getting almost as much light here with Light Cache only as we did with both Light Cache and Irradiance Mapping in our previous exercise.
This is because Light Cache rays don't just bounce once; like photons from which this technology is derived, Light Cache rays, once they have been cast out into an environment-- that happens from the camera's point of view-- they will actually perform multiple bounces automatically, and they can do that very, very quickly. In fact, this is Light Cache's big strength. Unfortunately, you can see, as well as getting the speed and lots of light bouncing around our environment, we also get a very noisy end result in our render.
So clearly, we're going to need to revisit our Light Cache controls to see if we can improve the situation a little bit. Well, probably the first control we would think of working with is this Subdivs value, which again can be thought of as quality control for Light Cache. This really handles the number of rays, or samples, that the Light Cache system would use in its GI calculations. So let's see what would happen if we doubled our default value. Let's set a Subdivs value of 1600 in there and again, let's take a render.
Well, there is no doubt, looking at the final render, that we have most definitely improved our noise situation. But if you're following along with this particular exercise file, you'll have noticed that that render took considerably longer than our previous attempt. And of course, while we have improved things, we can see that we still have lots of blotchy noise present in the scene. You'll also notice that the transition areas between our direct and indirect illumination are also looking extremely rough. Naturally, at this point we would be tempted to go and increase our Subdivs value a little bit more, see if we can get a little bit of extra quality out of the scene.
But truth be told, even if we increase that Subdivs value up to something around about 5000 to 6000 in this scene, we would still encounter these particular problems, and of course our render times would increase by an even greater margin. Can we then, as with our Irradiance Map exercise, work with some of the other Light Cache controls in order to improve the solution? Well, let's go back into our Options Editor. One option that we may decide to work with, or may try to work with, would be these Filter Samples. Essentially more filter samples would mean a more blurry, and so less noisy, Light Cache solution.
As filtering doesn't really add an awful lot to render times, let's bump this up to something quite high, like a value of 30, and again just close down the Options Editor and test that out. Well, quite clearly, we have been able to smooth out our noise problems by quite a considerable amount; however, we now run into the problem that always occurs whenever we increase blurring or interpolation operations inside a GI system. You can see we really are starting to lose definition in our scene.
It is very difficult to pull out scene detail. We are getting lots of flat-looking areas simply because we're now creating such a large blurring operation inside the solution. Now we could counter this a little bit by going and enabling Ambient Occlusion inside of our Indirect Illumination controls. This is found just towards the top of our Indirect Illumination rollout. That would add a little bit of definition back into the system. But still, we would encounter the problems that we see. Coming from Light Cache, we would still see some of that loss of definition, and of course, our transitional areas between direct and indirect illumination are still looking very rough.
Again, we could try tweaking some of the controls available to us, so we could try and work with our Filter Type inside off the Light Cache rollout. We could try and work with our Filter Size a little bit to fine-tune the filtering. But ultimately, we would just have to acknowledge that Light Cache just does not work very well when set as the primary bounce engine, which of course is not at all surprising, as really this technology has been designed to function as an excellent secondary balance engine, which of course it is. In fact, you saw I've demonstrated in our Irradiance Mapping exercise.
So again, in this video we've spent a little bit of time showing you how we can quickly and easily create a Light Cache GI solution. We have demonstrated a couple of the quality control settings available to us, but ultimately we have discovered the Light Cache is just not very good when set as a primary bounce engine. Do remember though, all of the controls, everything that we've talked about here, are applicable to Light Cache when it is set as a secondary bounce engine also. Let's move on then to our next video where we'll take a look at the last of V-Ray's GI systems that we'll consider in this course.
This is the Deterministic Monte Carlo, or DMC, Engine.
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