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Final gather is the automatic calculation of bounce. Light bouncing off of diffused surfaces, not mirror reflections, but, scattered reflections or ambient light. This is rendering with file and gather disabled. Let me clone that off so we can compare it. And, minimize that. And then let's go into the Global Illumination tab, in the Render Setup dialogue. And enable final gather. There are some presets here, but I do not recommend using these presets.
The presets frankly, actually make no sense. And they have way too high of quality settings for no reason. There's no real reason why you would ever want to do this. For example, up on here on very high, it's got crazy mad high values here. The idea of final gathering is to produce a kind of wash across the scene. And with these extremely high settings it's going to take an incredibly long time to render, and it's going to have super highly detailed bounce.
But for no reason, you will not be able to tell much difference on the screen. So it's important to know how to optimize this. Don't use these presets. Really, they're not helpful. The first parameter here is the initial final gather point density. That's the number of rays that are coming out from the camera. The low value here is about 0.4, really the optimal value I've found is a value of about one. And you can bring it down from that, I actually have used values lower than that. But really have had no occasion to take it up past one, or maybe two at the very most,but really, one is the optimal value.
The next parameter here is the rays per final gather point. What happens is that rays shoot out from the camera, and hit surfaces. And then from there, additional rays bounce off of that surface to test other surfaces nearby. And this is the number of rays that bounce off. And I've got a value of 150 here. That's actually kind of high. We can bring that down a bit, to maybe like 100 or so. Now we have the interpolation. This is the blending. If you have a lowish number of rays and a high blending then you'll get a nice wash that will render quickly.
So instead of cranking up the number of initial rays with the number of bounce rays, and then having a low interpolation. Instead we should have a moderate number of initial rays and bounce rays. And have a interpolation of again like 100 or more. And then finally this is an important attribute here. This parameter, diffuse bounces. This is the number of additional diffuse bounces. So you're always getting one diffuse bounce for free.
If final gather is on, you're always getting one bounce. In other words, a light wave is hitting a surface like the table here. And then bouncing off that and hitting another surface. You're always getting one diffuse bounce. You can increase this value up to as many additional diffuse bounces as you want. I would a recommend a value of exactly one. Anything more than that is not going to really show up on the screen, and there are some tool tips here, if you hover your mouse. Frankly, don't believe these tool tips.
It says here, typically a value of four to seven is required for accurate interior renderings. That is absolutely not true. If you increase this up to a value of four or seven, it's going to take forever to calculate the final gatherer. I mean it's going to take hours per frame to calculate, and it's just unnecessary. Again, this is the optimal value, exactly one diffuse bounce because after one bounce, the energy is, so diminished with each additional bounce that we will not be able to even see it on the screen.
So these are the values that I recommend and these are kind of easy to remember, one, 100, 100, and one and click Render. So the final gather phase takes a little bit longer now because it's more accurate, and it's going to look better. But not that much longer. I mean, if we had used those recommended settings it would take a really really long time. It would take several minutes just to calculate the final gather phase. All right, cool, and so now we've got a really nice result here. We're seeing final gather on the figure as well as on these other objects.
And we'll compare that once again to the version with no final gather. And you can see it's brightened up. And it's significantly more realistic now. So final gather is a very powerful tool. It is enabled by default, and the settings in those presets are not helpful. So I would say, always have final gather turned on, when doing a Mental Ray render, but tweak these settings. And again, you're rule of thumb is you want a relatively low number of initial rays, a low number of bounce rays, but a high interpolation value in order to soften up the effect.
And exactly one diffuse bounce is optimal.
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