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When working with V-Ray tools, such as lights, cameras, materials, and many others, we will often come across a subdivs -- short for subdivisions -- parameter. Understanding what that term refers to, and how our numeric subdiv values will be affecting our final renders, is another critical concept that we will benefit from understanding. Now, we have, of course, already covered the bare bones of the ray-trace rendering process, We have discussed how our renderer collects samples from our 3D environments by means of rays that are cast, and traced through that environment.
This initial phase of the ray-trace rendering process is handled by our image sampling, sometimes called anti-aliasing controls. If we just come up to the main toolbar, and click on our Render Settings window, we can just quickly show you where those controls are found. So inside of the dialog, let's come to the V-Ray tab, and by default, we find ourselves looking at our image sampling controls. These are the ones that will determine -- these will control the number of primary, or I-rays, that are used in this as we say initial phase of the rendering process.
If you recall, though, we also made mention of the fact that secondary, or bounced rays may also need to be calculated, depending, of course, upon the surface properties of our scene objects. These secondary rays are required to produce many of the effects that ray-trace renderers are so good at. Effects such as those seen in our slide, so reflections, and refractions, both glossy, and blurry, depth of field, motion blur, accurate area, or soft edge shadows, ambient occlusion, and quite a bit more.
The final quality of these effects will, to a large extent, be controlled by the number of secondary rays used to calculate them. The number of secondary rays used will be controlled by our various subdiv values. Now, let's just quickly show you a number of areas inside of the Maya UI where we will run across this subdivs value; this subdivs parameter. So for instance, in our image sampling controls, you see we have a Minimum and Maximum subdiv setting. If we come across to the Indirect Illumination tab, you can see we have a Subdiv parameter inside of our Irradiance map controls.
Come all the way down to Light cache, and we have Subdivs inside of those parameters. Let's go and pull up Hypershade window for ourselves. And if we just select a V-Ray material, and come into our Attribute Editor; make it so we are viewing it. And again, if we look inside a number of parameters in here, you'll see we have subdiv settings. So inside of Subsurface Scattering, if we come up to our Refraction controls, we have a Refraction Subdiv setting; up to Reflection controls, and we have Reflection Subdivs, and we could go on.
There are quite a number of areas inside the Maya UI where we will run across this subdivs parameter. Now, rather than being the actual number of samples used, the subdiv value represents the square of them. The value really describes the number of times each pixel will be subdivided, with of course, new rays being cast from each new subdivision pixel. So, a subdiv value of 8, as we see here, which oftentimes is the default in V-Ray, could more accurately be described as 8 multiplied by 8, which means we would get a total of 64 samples, or rays per pixel that could be used to produce a specific effect.
So hopefully you can see that our subdivs values will clearly impact the final quality of any secondary ray effects found in our scenes. However, there is another controlling V-Ray that will greatly influence just how many secondary rays are used. This is the DMC sampler, and it is our next critical concept for discussion.
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