Monday, April 25, 2011

Mental Ray Sampling cont. -- Min/Max method

This is a multi-part post continuing with findings related to Mental Ray's various "Sampling" settings in 3ds Max. The test scene (taken from a recent project) involves an exterior with a camera fly-down. Included in the scene is a parking lot with 3D stripes on a terrain surface and later, a view from near the surface of the parking lot with a few street signs casting shadows. Both the stripes and the shadows figure strongly in decisions related to the sampling settings required to create a quality rendering, both for an animation and for still shots.
First some examples to help make some decisions about utilizing the "Minimum Maximum" sampling option. The "Fast Rasterizer" and "Min Max" options are mutually exclusive with some different choices related to quality and speed of render. In a previous post I mentioned that the Fast Rasterizer method seemed a better choice for speed vs quality and the examples in these next 2 posts will bare this out with one exception which I'll note later. Before we discuss the issue with animations, lets take a look at some single frame renders. Note that all the following renders are zoomed in portions of a full frame at 640 x 360. The zoomed in region will make the differences presented more easily seen. We are interested in settings to create the final beauty shot here, not previews or test renders.

Example 1 shows a render with the Minimum Maximum method set to 1 and 16 respectively. No pixel will be sampled less than once. A decent setting but as the render shows, the parking lot stripes barely even show up, so this is not a viable option for a quality render and so not worth discussing further. (Note that 3ds max considers this to be a "High" quality setting).

Example 2: So what happens if we increase the Minimum to 4. Notice that it's an improvement, but some of the stripes either don't show up or show up poorly:
Example 3: Well, what if we increse just the Maximum option (1 and 64 repsectively). Again, missing or poor quality stripes:

Example 4: If we use 4 and 64 for min and max respectively we'll get an acceptible rendering:

All of the above renders used the "Box" filter set to 1 x 1. Render time for the full frame of the last sample at 4 and 64, min & max, was 1:33. As a comparison, here is the same render with the "Mitchell" filter set to 4x4 which provides a slightly better anti-aliasing computation at the cost of a little more render time (1:53):

In the next post we'll look at the same scene and views with the Fast Rasterizer.

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