Using the Fixed-Rate sampler

If you recall, in our earlier theory work on image sampling we learned that rays and samples are used to gather lots of information from our 3D environments, the end result of course being the computing of the final pixel color values that will be used in our rendered images. The V-Ray renderer gives as a choice of three different engines that can be used to handle this part of the rendering process. If we just come into our 3ds Max Render Setup dialog, we open that up, come into the V-Ray tab, and inside of the Image sampler rollout, if I just choose this dropdown, you can see we have three choices available: Fixed, Adaptive DMC, and Adaptive subdivision.

In this particular video, we are going to focus on using the fixed-rate image sampling engine. Now the fixed-rate sampler performs image sampling in really a very straightforward way. It uses, as you would perhaps have guessed, a fixed number of rays per pixel to accomplish its information gathering in the scene. Now with subdivision value of 1 set, this is the controlling parameter that we will use to determine the number of rays. With this value, a single ray is sent out from the center of each pixel in our render.

Whatever that ray hits in the scene, that will determine the color value for that particular pixel. With a Subdivision value of 1 set, let's jump into Adobe Bridge and just show you the kind of render--I'll show you the render--that would result from our scene with this particular image sampling setting. Now you do of course have access to all of the images we will be looking at here. So we'll just show you how you can navigate to them. So come into your Exercise Files folder. We need to find our renderoutput folder, come to Ch06, and of course, we're working with the fixed-rate engine.

Now if I just click on this image and then use my spacebar to maximize and then left-mouse click to really pull things to 100% viewing, you can see the results that would come from that image sampling setting, that subdivision value of 1, in the fixed-rate engine. Now if you remember, we said that some of the challenges in the scene were our straight lines, and you can see that they are not faring too well at this moment in time. We mentioned that our shadow sampling would present a challenge. We have ambient occlusion.

You can see lots of noise coming up in the corners. We have our very fine straight lines that, as you can see, are really not working out at all. And if we come down here, you can see how our very noisy materials are fairing here, in fact, so badly that we have lots and lots of moiry patterning taking place here. The image sampler really doesn't know how to resolve the information that it is finding in this particular material. So all in all, the challenges that we've set, not really fairing too well at this moment in time. In fact, you can see along geometry edges we are getting lots and lots of stair-stepping because the image sampler just doesn't have the information that it needs to work with.

Clearly then, we need to increase the quality settings if we want a little bit more out of this image sampler engine. So let's jump back into 3ds Max, and we'll just set a Subdivision value of 2 here. So we'll double what we have. Now we are getting four samples evenly distributed across each of the pixels in our render. The four samples will be averaged together by the engine to produce a final pixel color value. So again, let's come and take a look at what that gives to us. Just use the spacebar and we can select our second image, and then spacebar to pull out up to full screen, and just use the left mouse to zoom in fully.

Now you can see that our effects are starting to clean up a little bit. You can see the lines are faring a little bit better, our noise in the shadow areas starting to clean up somewhat, and if we come down to the bottom, you can see that suddenly we are getting enough information now to clean up most of those moiry patterns, although we are still seeing there is lots of missing detail in here. We have, of course, doubled our render times, but seeing as we're still rendering our 1000x1500 pixel image at just short off two-and-a-half minutes, we are still not doing too bad, and we can see we're getting some good feedback from our scene.

Well, let's push the quality settings. Let's go back into 3ds Max and set our Subdivision value up to 8. So that's a quite a significant jump in terms of the subdivisions we are using. Let's examine how things are looking in Bridge. Let's come to our third render, spacebar, and left-mouse-click. And now you can see that things really are starting to clean up quite nicely. We are getting very little detail on our diffuse texture, the wall texture. You can see our shadows are cleaning up, the lines are starting to resolve quite nicely. And again, you can see how we are starting to pick out some detail in our very noisy pattern.

Still a little bit of noise in our diffuse textures, so that may be something we'll need to work with. But again, you can see that we have really significant jumped now in terms of render times, just over 17.5 minutes. What though if we wanted to really clean up this scene? Well, let's jump back into 3ds Max, and let's again double the value that we are working with. We'll work with 16 subdivisions here. Let's use the spacebar and grab our final fixed-rate image and now as we just look slowly at this image, you can see pretty much everything has cleaned up very nicely. Indeed, we're getting lots and lots of quality from all of the challenging areas that we've placed in this scene.

The fine noise has disappeared off our diffuse texture, our soft shadow is looking very nice indeed, but we are one hour and eight minutes. Now the fixed-rate engine does have quite a significant weakness. There is no adaptivity whatsoever built into this system. V-Ray will use the fixed value of subdivisions of samples that we've set in our image sampler controls whether our scene, whether our image requires them or not. This, of course, can lead to long render times that may still leave us with an unsatisfactory level of quality in our renders.

For this reason then, the fixed-rate engine is generally speaking best suited to being used for quick and easy test renders. You saw that we got a reasonable amount of feedback with our low settings and we were getting pretty fast render times. What we want to do now is to move on to a system that does have adaptivity built into it, and this is the Adaptive DMC image-sampling engine.