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You can use the High Samples setting in the mental ray Area Light section of the Attribute Editor to improve the quality of the shadows cast by the area light. I'm going to do a test render here. We're using the default settings. So, we could see that the shadow is soft, but it's also fairly grainy. So, I'm going to save this image, minimize this, and I'm going to double this to 16, and create another test render.
It's going to add a little bit to the render time, but it is going to start to improve the quality of the shadow, so we can compare what it looks like before to after. It's a bit subtle. I'm going to zoom in here to make it a bit more obvious. This is with the High Samples set to 16, and this is High Samples set to 8. So you can see that there is a difference there. So, as you're tuning your shadows, you're going to probably want to increase this slowly and test as you go.
Area lights, by their very nature, are usually going to take a bit longer to render than other light types. So, that's something to be aware of when you start to add them to your scene. The more area lights you use, the more you're going to add to the render time. But this has already starting to look very nice. We can even see the shadows cast by the chairs here. It looks pretty good. The other settings here, the High Sample Limit and the Low Sample Limit, these are both related to how the shadow appears in reflections. So I have a mirror in this scene, and I'm going to unhide it by pressing Shift+H. It's just a polygon plane, and has a reflective blinn shader applied to it. Reflectivity is set to 1.
So I'm going to make sure that everything is reflected on the plane. I'm going to create another test render. So, this is a common mistake to make is to forget to adjust the settings so that the shadow appears in the reflection. So, what I'm going to do is I'm going to minimize this, and scroll up here to Ray Depth Limit. I'm going to set this to 2, which will ensure that the shadow does appear in the reflection. I'm going to render the region again.
Now, we can see the shadow. You can clearly see that this shadow is a bit lower quality than this shadow. The reason for this is this is actually a more efficient way to render, because in many scenes you might not be necessarily concerned with the quality of the shadow and the reflections. Now, in this case I'm using something that's 100% reflective, so it's a mirror. But if this was something like a window, or a metal piece - like the candlestick, or something like that, I probably don't want to worry about getting absolutely perfect shadows and the reflections of things like metal objects.
So, in this case, having a separate control for that quality is very useful. This basically says, how many times is this shadow going to be reflected before it uses the Low Samples setting, as opposed to the High Samples setting? So, in other words, if I set this to 2 and do a test render, what it's going to say is, okay, you can cast that shadow on two surfaces, one and two, and each time you do that, you use the High Samples Limit, which is set to 24.
So this is going to make the render take a little bit longer, but you're going to see that the shadow quality in the reflected surface looks very nice. It looks just as good as this. If I had a third reflective surface in here, like another mirror over here or something like that, that mirror, these shadows would look lower quality. They would have a sample limit of 1. So, if increase this to 3, then all three services, the table and the two mirrors would use a High Samples Limit of 24. So this is important to know because it's tempting when you're trying to tune the look of the shadows to just start pumping up anything that says samples to a high level.
If you do that, and there are no reflective surfaces in the scene, you're not going to see any difference, no matter how high you set this, or how high you set that. This is the only control that's going to make a difference in the way that your shadow looks on the initial surface. So, only use these two settings when you have reflective surfaces in the scene; otherwise, you're just basically wasting time.
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