使用Mental Ray模拟全局照明
'Simulating Global/indirect Illumination with Mental Ray' lcfX(~/m^by Richard Minh Le
翻译：esau2
原文链接：[url=http://www.3dtotal.com/team/Tutorials/GI_MentalRay/mentalray_01.asp][color=#2f5fa1]http://www.3dtotal.com/team/Tutorials/GI_MentalRay/mentalray_01.asp[/color][/url]
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_db8cb49b3423c5d.jpg[/img]
Mental ray, a product of the Mental images, Inc, is the first rendering engine, which simulates the physically correction of the real light and reaction of surfaces to light. Together with Renderman, by PIXAR, mental ray is recognized as an industry-standard rendering software; and has been a major contribution to world-wide design visualization and feature film, including Oscar-awarded winning movie Spider-man for the best visual effect. Mental ray has been integrated into Softimage|3D and Softimage|XSI, Autodesk 3ds max, Alias Maya, Side Effects Software's Houdini 5, SolidWorks PhotoWorks 2, and Dassault Système's CATIA V4, V5 products, only in 3ds Max 6+. In the real world, light energy bounced off from one surface to another, causing some received-light surfaces to be secondary emitted-light ones. That's why illumination would be more even and interesting (in some senses). In 3d graphics, however, it does not happen by default, and users have to tell the software to simulate a system of bounced lighting. There are already two methods of generating this in Max, which are Light Tracer and radiosity. Mental ray is a newly-added one, based on different technology.
Interior scene: （室内场景）
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First, download the scene file, then follow me. Open INTERIOR_LIGHT_MAX8.max from the directory. This is an imaginary cartoon-like space which shows a group of teapot trying to hide from the another. The renderer is currently set up to be Default Scanline. Also, the resolution is set up to 400x565 for testing/learning purposes. Lighting system includes one Photometric Area Light.
（场景默认使用扫描线渲染。灯光系统包含一个光度学面积灯。）
1.Hit render (F9) to start evaluating the render.
（Ｆ９渲染察看。）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_855db57715d7b4b.jpg[/img]
The scene generally looks boring as it is very shadowy and unrealistic.
（现在场景非常阴暗，不真实。） 2.Menu bar/ Rendering/ Render… OR hit F10. First, In the Render Scene window, scroll all the way down to the bottom and Open Assign Renderer roll-out. Second, click on the”…”button next the Default Scanline Renderer words, then choose Mental Ray.
You will immediately notice the change in the window layout. The two tab, Advanced Lighting and Raytracer, are replaced by Indirect Illumination and Processing. For the purpose of this tutorial, I will only talk about some of attributes in the Indirect Illumination tab.
（Ｆ１０更改渲染器为Mental Ray.注意渲染面板的变化。)
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_b4149095943d2b3.jpg[/img]
3. In the Indirect Illumination tab, Global Illumination group: - check Enable, leave the Photons: 500 Hit render (F9)
（在间接照明面板，全局照明栏，勾选ｅｎａｂｌｅ，调整每个采样使用的最大光子数为５００。）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_43f4f94966cc2b1.jpg[/img]
The scene now is filled with a number of photons, carrying a lot of energy. Their color assumes the color of the last surface they hit. The size of these photons is based on the scene size (normally about 10% of the scene with Maxium Sampling Radius unchecked)..
（现在场景被光子填充。他们的颜色代表了最后所撞击的表面。光子的大小取决于场景的大小——如果最大采样半径没被勾选，那么一般使用场景的１０％。）
4. In the Light Properties group: Increase the Average GI Photons per Light to: 20,000 Hit render (F9)
（在灯光属性栏中，提高每灯发射平均ＧＩ光子数为２００００。）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_23c9a1e1c9e8f70.jpg[/img] 5. Increase the Average GI Photons per Light to: 50,000 Hit render (F9)
（增加到５００００的渲染结果。）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_efbd1399da4187a.jpg[/img]
The photons start to blend.
6. Increase the Average GI Photons per Light to: 100,000 Hit render (F9)
（增加到１０００００的渲染。）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_71e7607abe2dc8f.jpg[/img]
7. Go up to Global Illumination group and check Maxium Sampling Radius to 20. This helps blending those photons. Hit render (F9)
（在全局照明栏，勾选最大采样半径，并设置为２０，这将有助于混合这些光子。）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_4ec3c8b9ae8461b.jpg[/img]
As you can see, the GI effect starts to be more visible. However, it leaves the artefacts because of the photon granularity. The photons alone cannot be enough, so, we will have to use Final Gather to fine-tune the image, and take the effect of the Skylight. Mental ray's Final Gather works the same way with Regather in radiosity. It samples the scene rendered pixel, or averages between sparse samples.
8. In Final Gather group:
- Check Enable ZoroK.
- Set Samples to: 300 (1000 by default, but we need only 300 for testing purpose)
Hit render (F9)
（打开最终聚集，设置采样为３００，默认是１０００，对测试而言３００足够了。）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_cbadd62f72b87ba.jpg[/img]
Global Illumination effect is now clearly visible, contributed by the Skylight. But, now, we have a problem. First, somewhere in the scene look a bit dark, as should not be. Second, the artefacts have not really been fixed; and shift to the shadow.
9.We are now safe to move. So, Uncheck Preview (No Precalculations) and increase the Samples to 50. Also, check Radius and Min. Radius and adjust the value as shown.
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_72a6023cff233c0.jpg[/img]
The color bleed effect is now also visible, you can see it where those teapots on the fore-ground floor are. However, it seems like we need more Final Gather samples to finalize this render
[[i] 本帖最后由 火柴盒 于 2008-10-28 10:16 编辑 [/i]] 10. Increase Final Gather Samples to 150
（提高最终聚集的采样值为１５０。）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_05a354e5ea0edb3.jpg[/img]
11. Here is the high-res sum-up
（下图是高分辨率的渲染结果。）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_97a4ab2249b1a57.jpg[/img]
Some areas look overbright and has mirror artifact, but it is up to you to tweak more as we are only explementing the workflow. So, At this point, you should have an idea of rendering with Mental ray Exterior scene: =SV b k
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First, download the scene file, then follow me. Open EXTERIOR_LIGHT.max from the directory This is an imaginary cartoon-like space which shows a group of teapot trying to hide from the another. The renderer is currently set up to be Default Scanline. Also, the resolution is set up to 400x565 for testing/learning purposes. Lighting system includes one mr Area Spot to simulate the Sunlight. uS7kkzt-x
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1. Ok, so, the same start we have here. S<eB&qT$
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_b1cc3c60145dd69.jpg[/img]
2. Now, Go straight down to Final Gather group and check Enable:
- Decrease Samples to 20 (to those people I know, they leave it 1000 and render. Please dont as it is a big oh-my-god).
- Check Preview (No Precalculations) to test for now as the render appears patchy, but no FG calculations.
- Also, In the Trace Depth group, Increase Max. Bounces to 1. This is an alternative of Photo Mapping, however, it is less accurate.
Hit render (F9)
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_a21674844e385de.jpg[/img] 3. We are on the right track. So:
- Uncheck the Preview (No Calculations)
- Push the Samples to 50
- and Max. Bources to 3
Hit render (F9).
（我们已经步入正轨了。
取消预览，提高采样值到５０，追踪的最大反弹值设置到３。
Ｆ９渲染。）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_31346321f9132bf.jpg[/img]
We can now start to get rid of the artifacts.
（现在我们要开始去除这些噪点。）
4. Check Radius and Min. Radius. So, we can tweak these as we wish.
（勾选半径和最小半径，按需要调整。）
Hit render (F9) ,
（Ｆ９渲染。）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_2d77a64e60f869b.jpg[/img] 5. With the value of Radius and Min. Radius as following, the render shows some improvements.
（调整半径的值和最小半径的值，渲染结果显示出一些提升。）
Hit render (F9).
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_471790a316efbef.jpg[/img]
6. To finalise, increase the Samples to 100.
Hit render (F9) .
（为了完善它，将采样值提高到１００，单击渲染——Ｆ９。）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_6f6220e990ca2ee.jpg[/img] 7. Here are our final high-res render
（下图是最终的高分辨率渲染图像。）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_618972ec6002858.jpg[/img]
Same scence, different light direction.
Happy rendering!
（同一个场景，更改了灯光的方向。一个愉快的渲染过程！）
[img]http://bbs.ew3d.cn/attachment/Fid_9/9_11_9627dfbb2f9b331.jpg[/img]
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