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The settings that determine the quality of your rendered images are, of course, found in the Quality tab for the Render Settings window, when you are Render Using is set mental ray. So, let's take a look at this tab. So there are a number of Quality Presets that you can use. As you change from one preset to another, you can actually see these settings down here will change. So, if I go to the Production setting, you can see how the sampling has changed automatically. So, I want to take a look at a low-quality render.
So, I will set this to draft. In the case of this particular scene, I have Final Gathering. So, I am going to turn Final Gathering back on. As I switch presets, depending on the Preset that I am using, this may be on or off. In other words, if I switch to a preset that doesn't use Final Gathering, it will turn it off automatically. For example, if I switch to Preview, you will see that this was turned off. So, that's something you should be aware of. If you are going to use Final Gathering, and you change from one preset to another, double-check your Final Gathering settings. In some cases there are - this preset, for instance, has Final Gathering so it will turn it on for you if it's off.
Let's switch to the Draft preset. I will turn the Final Gathering back on and do a render. So, with the Quality set to Draft, you can see that the image quality itself if fairly low, and this is most noticeable along the edges of the surface. If I zoom in here, you can see that the edges are very blocky. This is also true for some of the details around here. This is because, of course, computer, images, or images generated on a computer, are made up of pixels, which are just square blocks of color.
Anti-aliasing is the amount that the colors are blended along the edges in order to create the illusion of a nice smooth edge. So, at the draft quality, we can see that even when I click 1:1 button here, it shows the image at 100%. Then you can see at 100% the actual image size, it's very apparent that the edges are quite rough. So, I am going to store this image and minimize the Render view, and I will go to the Quality Presets, and I will switch to Production. Then you see who these settings change, and I will get to these in just a moment.
I am going to go and turn my Final Gathering back on and create another test render. When I use the Production preset, see how the edges are smoothed. So, I will store that image, and we can compare it to see the difference in quality. So, I am going to zoom in here, and as I move to this stored image to this one, you can see how the colors have been blended together. In Draft quality, it's quite low. There is not as much blending going on; at the Production quality, it's much smoother, even when I am zoomed in.
For most of your Maya renders, you will probably find that the Quality Preset does a pretty good job, but if you run into a situation where you actually need to improve the quality beyond the Preset settings, at that point you are going to want to start to work with the controls here in the Ray Trace/Scanline Quality section. The production setting uses a Max Sampling Level of 2. To understand what that means, you can take a look at this little hint here that Maya is giving you. This means that at least one sample per pixel - at most, 16 samples per pixel.
As I move this up, if I set this to 3, it will say at least 4 samples per pixel, at most 64 samples per pixel, and you can see at level four. So it's essentially quadrupling the maximum level of samples. So, what exactly does this mean? Well, as mental ray shoots rays into the scene and starts sampling the objects in the scene in order to create them into a two-dimensional image comprised of pixels, it's going to look at each sample point in this scene as it's rendering and take a look at the neighboring points and determine, based on the contrast between the initial sample and subsequent samples, how many samples per pixel, and you can control how mental ray determines this by lowering the Anti-aliasing contrast.
The lower this value is, the more likely it's going to create more samples per pixel. If I set this down to .05, there is going to be a higher chance that it's going to use more than one sample per pixel as it renders. So, generally speaking, if I am trying to fine-tune the quality of the images what I will do is I will adjust this value first. I will go in here and lower this by a little bit, do a test render, and compare to see how much I like it. If I can't get what I need out of lowering this value, at that point I will start to increase the Max Sample level.
This will add a lot to render time. If I increase this, if I decide the 2 is just not enough, and I increase this, I will also set this back up to .1, do some test renders, and again, lower this value gradually until I get the image that I need. You can actually get a visual indication of how mental ray is sampling the image by turning on Diagnose Samples. So, this will show you an image where you can see where most of the anti-aliasing is going, or where most of the samples are devoted.
So, I am going to turn this on, and make sure my Final Gathering is back on just so - the Final Gathering in this case is not going to have any bearing on the Anti-aliasing, but in order to be consistent with the other renders that I have created, I am just going to turn it back on. So, now that this is on, I will create a test render by clicking on the Render Clapboard icon. We are going to see the image, as we are used to seeing it, and now we are going to see a second pass, and in this second pass we are going to get a color representation. So, everywhere you see light colors or white colors in this grid is where mental ray is increasing the sampling.
So along the edges and around the specular highlights, because there is more contrast between this area, and that the contrast between here and here is greater, so it's going to create more samples in this area than it will, say, around here, where the contrast is low. So this is another way to double-check your images and see exactly how mental ray sees the scene while it's rendering. But overall, I think for everyday rendering the presets will get you what you need.
It's only in rare situations where you have a very complex scene that you will have to start adjusting the sampling quality.
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