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If you recall in our earliest theory work on Image Sampling, we learned that rays and samples are used together lots of information from our 3D environment. The result, of course, being the computing of the final pixel color values for our rendered images. The V-Ray render, it gives us a choice of three different engines that can be used to handle this part of the rendering process. If we come up to our Main toolbar and open up our Render Settings window, and if we come into the V-Ray tab, we find ourselves by default in the Image Sampler rollout, and you can see have this Sampler Type dropdown.
If we access that, we can see three engines listed, Fixed rate, Adaptive DMC, and Adaptive subdivision. In this particular video, we're just going to be focusing on the first there, the Fixed rate sampling engine. Now the Fixed rate sampler performs image sampling in a very straightforward way. It uses, as would perhaps have guessed, a fixed number of rays per pixel to accomplish its information gathering. Now with our Subdivs value set to 1, what we get is a single ray sent out from the centre of each pixel for our rendered output.
Whatever that ray hits in our scene, will be used to determine the color value for all of this particular pixel, the pixel that this ray has traveled from. Now with that Subdivs value of 1 set in there, what we're going to do is jump into Adobe Bridge. We're just going to use some pre- rendered images to show you how the changes made in our image sampling engine affect the rendering of our scene. Image sampling is, of course, a render intensive process. So we just need to work with these images just to make the process nice and smooth. So let's jump over to Bridge.
You can follow these steps because we have these images inside of your Exercise files folder. So let's go into there, let's come into the Assets folder>Chapter06 and we're looking at of course our Fixed Rate engine. So let's select the first image. I am just going to use the Spacebar to maximize and then left mouse click to really zoom in. And you can see that we get not a bad image, but we can see that there are lots and lots of problems with it. You can see geometry edges are getting a very obvious stair-stepping effect.
We can see there's lots of noise present in the scene. Our lines on the objects are not fairing too badly. They are resolving quit well. You can see again, stair-stepping off the edges of the geometric objects, lots of noise on our diffuse textures. Our noisy texture is not fairing too badly in this instance; they are cleaning it up quite well, and you can see we have a Render Time, a very fast Render Time of 1 minute and 39 seconds. This is a 1000x1500 pixel render. Of course, we need to push the sampling quality if we want to clean things up here.
So let's jump back into Maya, let's come to our Subdivision settings, and let's increase now to a value of 2. This means that we are now getting full samples, evenly distributed across each of the pixels for our render. These four samples will of course be average together by the render. That will allow it to produce again a final pixel color value. Let's jump back into Bridge with those changes made. I am just going to Spacebar to exit and then select our second image, Spacebar, and then left mouse click to maximize, and you can see we're starting to clean things up somewhat.
Our geometry edges are not looking quite as jagged. We've got a bit of cleanup of the noise in the scene but still a very obvious problem, and now we're at our Render Time of 2 minutes and 28 seconds. So still fairly fast we're getting lots of nice feedback from the scene, but again, we've really not got anything that we would try to use as a final render. So again, let's go and push the Image Sampler's quality by adjusting our settings. This time we want to set our Subdivs value. Let's jump all the way up to a value of 8.
With those changes made, let's come back into Bridge and examine our third image. And what you can see is that we start to clean up our scene very nicely indeed. We're cleaning up the Shadow areas, all of the geometry detail is looking very nice. Of course, we have jumped now all the way upto at Render Time of 20 minutes and we still haven't cleaned up all of the noise. You can see lots of fine grain noise on our diffuse color block here and just some noise definitely present still inside of the shadows.
So one more quality setting change then, let's go all the way now up to a value of 16. This means we're using 256 samples per pixel for the sampling inside of our image. So back into Bridge and select our final image, Spacebar, and then left mouse click and what you can see is that we really have cleaned up our scene quite nicely. All of the line detail looking nice, shadow detail, not looking too bad at all, our noisy textures are picking out lots of detail, but of course, we're now at a Render Time of 1 hour and 28 minutes.
Now we do need to remember that the Fixed rate engine will still be making use of the DMC Sampler Threshold value. So you may need to tweak those to clean up any extra noisy effects in the scene. But we're just sticking to using the Image Sampling controls for the Fixed rate engine in this exercise. One weakness or one downside of the Fixed rate sampler is that there really is no adaptivity in this system whatsoever. V-Ray will always use that fixed value, that fixed number of samples whether our scene, whether image requires them or not.
This of course can lead to long render times as we see and we still may not have a satisfactory level of quality in our final renders. For this reason, and really the Fixed rate engine is, generally speaking, best suited to being used for quick and easy test renders. Well let's move now onto looking at a system that does have adaptivity associated with it and that is the Adaptive DMC engine.
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