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One of the things that newer render artists could fail to grasp regarding their scene lighting is the role that materials often play in the actual bouncing of light around an environment. In this video, we just want to give you a quick demonstration of the important role that material reflectance plays in the global illumination lighting process. Reflectance, or diffuse reflection, should not be confused with reflectivity. Reflectance is the reflection of light from a surface, but instead of the incident ray being reflected at just one angle, as in the case of specular reflection-- that is, property that we call Reflectivity-- reflectance sees the ray bounce at many angles, hence the production of colored and matte-looking surface.
In this demo, we're just going to use different grayscale values in our default material to demonstrate the difference this can make regarding light's ability to bounce around an environment. Remember, as we perform our test renders, we are not going to be changing the amount of light in the scene, nor will we be adjusting our camera's exposure; that will be fixed at a value of 1.7. This gives us a nice interior exposure. The only thing we will work with in order to affect our scene lighting is the Reflectance value of our default gray material.
So let's make a start by first of all opening up SketchUp's Material Browser. Now I want to come to our In Model materials, which as you can see, consists of just one default gray material. Then if I come into the Edit tab, you can see we're going to make use of SketchUp's HSL Color mode, even though this is wrongly spelled inside of the Color Picker dropdown. Of course, we could make use of the Twilight Material Editor, if I just pull that off to one side of our interface. But if I just select our default material and then come into the color swatch, you can see, Twilight makes use of a typical 0 to 255 color range, whereas SketchUp's values run from 0 to 100. This just makes it a little easier to picture where on a sliding scale the color values we will use sit.
So let's set an initial Luminance value in our material of 20. This, as you can see, gives us quite a dark-gray material. To see how this affects our scene lighting, let's us open our Twilight Render dialog and take a test render. What we see of course, perhaps not unsurprisingly, is an extremely dark interior. You can see our ceiling is receiving very little light. The far end of the room is pretty much in blackness. We can just make a little bit of light bounce out, but we can't really see any light penetrating into that far space at all.
Clearly, for a natural-looking environment, we need more illumination in the scene. And as we've mentioned, possibly the first port of call would be to increase the intensity of lighting in the scene, to bring more light into our interior or indeed to work with the Camera Exposure control and try and lift the illumination levels in that way. But we can demonstrate now that oftentimes those steps are unnecessary when it comes to raising illumination levels in an environment. So let's come to our material and raise the Luminance value to 50.
Once again of course, we need to take a render. Now, as you can see, we have significantly increased our illumination levels. We're getting quite a bit of light coming up onto to our ceiling now. We are even starting to make out our far wall. We are seeing the light bouncing around that far end of the room. And we need to stress, all of this has been achieved without touching any of the typical lighting controls. We have just simply raised the Reflectance value of our material. Also interesting is the fact that we have only increased our render times by a single second.
As I would still like to get a little more illumination bouncing around this interior, I am just going to go and raise my Luminance value one final time. This time we will use a setting of 75, and again, we'll take a render. What we see now of course is an extreme improvement, in terms of the illumination levels found in our environment. If we take a look down to the far end of the room, you can see, we can clearly make out the wall at the far end there. We're getting what looks like natural light bounce occurring. And as you can see in this instance, we've not increased our render times at all.
This in fact is a behavior that you would see with any of the Easy_01 to 07 presets, as they use Photon Mapping and Final Gather as their GI system. Because photons are so good at moving light around an interior space, even the increased Reflectance values don't really add anything significant to the render times. Things would actually be considerably different if we use any of the progressive, unbiased Rendering Options available to us. In fact, if we just jump into Adobe Photoshop, here you can see we have two progressive renders taken using the Easy09 preset and rendered for 10 passes each.
Our first image is taken using our initial Luminance value of 20, and as you would perhaps expect from that setting, we have a very dark interior indeed, although we do get a little more natural light behavior. You can see the brightening of this right-hand side wall, where light is bouncing, but still, down on the far end of the room, we really can't see any light penetrating down there at all. Now this particular render, if we look at the image title, took 6.1 minutes to complete. Now if we switch over to our second image, which was taken using our final Luminance value of 75, you can see, well, we have much more natural, much more realistic-looking lighting in our environment.
As with our Photon and Final Gather option, we can see all the way down to our far wall. And again, even though we have a little bit of noise in there, we're getting what looks like natural light bounce. However, the render times for this particular image were considerably different. You can see here, 11.5 minutes to complete the same 10 passes. The difference in render time is occurring because light rays in our progressive render are continually being calculated. As the reflectance of the material rises, the light rays will bounce more and more often, and of course, as they bounce more, they require more computation.
This leads to increased render times. Clearly then, although seemingly separate disciplines, materials and lighting cannot be thought about, they cannot be dealt with, in a mutually exclusive environment. What settings we apply to one will affect the other, especially, as we've demonstrated, when it comes to getting light to bounce around an interior environment. So if we want to maximize our light transport or our light bounce, we need to make certain that we've given attention to our material's Reflectance values.
Just be aware though that as we increase reflectance, we generally have to decrease saturation in a material; otherwise, color bleed can become extremely strong, even overpowering.
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