19 December 2008

Introduction to Radiosity

This tutorial needs you to understand basic use of 3dsmax.

Introduction to RadiosityRadiosity help us to create more realistic scene by simulating how lights behave in the real world. In real life, light is bounced several times in other objects before our eyes catch them. This cannot be achieved using Standard Light in 3dsmax. That's why we need to use Advanced Lighting, term for global illumination used in 3dsmax (3dsmax is really fond of creating their own term, which I think un-necessary). The two global illumination options available to the scanline renderer are Radiosity and the Light Tracer. In this tutorial, we learn how to create scene for radiosity use.

1. First thing you need to consider is to create mesh object design specially to be rendered using Radiosity. This means we need to use proper unit setup and precise modeling techniques. Now, we are going to set system unit setup. Go to Customize>Units Setup. A window will appear. Then, click System Unit Setup button. Set your System Units Scale. In this tutorial I use 1 Unit=1 Centimeters. Click Ok when finished.

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2. After we set up Units Setup, create a box in Top viewport (300x400x250 cm). Then, create another box (120x15x250 cm). Shift drag this box to create a clone. Look at image below for reference.

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3. Now, we are going to apply precise modeling. This means we create each object has precise size. Walls should stick right to other walls, no gaps allowed. If there's a gap between objects, you will get leaked Radiosity when rendering. To apply precise modeling, you can use Align Tool (Alt+A). In Top viewport, select one of small box, click Align Tool, and click big box. In Align Selection window, activate Y Position only and choose Minimum and Minimum. Click OK. Repeat the same process with other small box. Right now use Maximum and Maximum in Y Position.

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4. Small boxes will be placed like image below. There's no gap between small and big box.

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5. Apply Normal modifier to big box. This modifier will flip all polygons. You will get a interior of a small room here

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6. Apply some materal to all boxes. For example I just apply grey color for walls. Create a camera inside the box. Adjust camera position until you get view like image below. Finished file can be downloaded here (zipped, 17kb, 3dsmax8 format). In of this tutorial, we will assign Radiosity.

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After we created necessary object used in this tutorial, we will begin to assign Radiosity. After we assign Radiosity, we need to calculate its solution. For complex scene, calculating Radiosity solution maybe very slow process, depend how fast your computer is. Fortunately, you need only to calculate Radiosity solution once, as long as your object is not moving. This is useful when you create walkthrough animation (the only thing that is moving is camera). Of course, if you change parameters in Radiosity, you need to calculate the solution again.

1. Continue your previous tutorial. If not, you can donwload 3dsmax file here (zipped, 17kb, 3dsmax8 format). In this file we have small room. There are 2 short walls divide the area. These walls textured using simple material, just grey color.

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2. Add a light to this scene. For example, I add Omni light (Standard Light type) and place it near the camera. Note: Radiosity work best using Photometric light type. This light type will be discussed in another tutorial.

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3. Activate Perspective viewport and do a test render (F9). Image below shows the result. As you can see, room is not well lit. Some areas too dark, and the others too bright. If you do not use Radiosity, you can add another light and adjust its intensity, work around until you get desired result. But, using Radiosity you can use only one light, just like room in your house that has one light too.

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4. Go to Render>Advanced Lighting>Radiosity. A small window will appear. Click Yes to assign Radiosity.

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5. Render window will be available to you (Note: you can always open this window by pressing F10 and click Radiosity tab). When you assign Radiosity, 3dsmax will state this plug-in is Active. You can activate or de-activate Radiosity anytime you want.

Before you render Radiosity, you must calculate Radiosity solution by pressing Start button. Radiosity calculation depends on how complex your scene and how fast your computer. Radiosity calculation for this tutorial should not be very long to wait. As a result, your Radiosity solution is shown in Perspective viewport. A little bit dark, but we will fix that in the next step.

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6. Now, we are ready to adjust several parameters. In Radiosity Processing Parameters rollout, Initial Quality=85% enough for most scene. If you change Initial Quality, you need to click Reset All and click Start again to re-calculate Radiosity solution. Increase Initial Quality if you want to get smoother result. Another important parameter is Indirect Light Filtering. Increase this value if your scene has too much noise (dotted). Usually value of 3 or 4 is enough. But, for this simple tutorial, changing Indirect Light Filter has little or no effect. Direct Light Filtering is only useful if you use Shoot Direct Lights. Note: you can interactively adjust these filtering values without re-calculating solution again.

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7. Under Filtering is Exposure Control. Click Setup button if you want to change exposure, or in other words setting Brightness and Contrast. Just like you change Levels in Photoshop. There are several option to choose eq: Automatic, Linear or Logarithmic. For this tutorial, use Logarithmic Exposure Control. Note: Exposure Control located in Rendering>Environment, you can open Exposure Control by pressing 8 in keyboard.

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8. In Radiosity Meshing Parameters, click on Enabled. If Meshing Parameters is active, 3dsmax will divide your mesh into smaller polygons to calculate Radiosity. How 3dsmax divide your mesh depends how your mesh size and units setting. For example, if you used Centimeters in Unit Setup, Mesh Settings will show like image below. When you need to have smoother result, decrease all Mesh settings values.

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9. In Rendering Parameters rollout, activate Regather Indirect Illumination. This option provides best quality rendering but takes more RAM to process. When finished, click Reset All and Start to re-calculate Radisotiy Solution again. When finished, click Render button.

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10. Image below shows differences between rendered image without and with radiosity. Finished file can be downloaded here (zipped, 85kb, 3dsmax8 format). In this tutorial, you will learn how to use material specially design to Radiosity, called Advanced Lighting Override Material. You will create a neon effect using this material.

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We have created scene first and radisosity solution in this tutorial. You may already knew that Radiosity is work best with material design specifically for global illumination. We can use Photometric light and Advanced Lighting Override Material to increase result when using Radiosity. Photometric will be discussed in another tutorial. This tutorial will discuss about Advanced Lighting Override Material only.

1. Continue your previous tutorial, or download max file here (zipped, 88kb, 3dsmax8 format). This file has a scene already assigned with Radiosity. Let's begin by creating a text in Left viewport. For example, I create an X letter. After that I apply Extrude modifier and add thickness to this letter.

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2. Open Material Editor. Select unused material slot. While letter object still selected, click Apply Material to Selection button to assign this material. Then, clcik Standard button. In Material / Map Browser window, click Advanced Lighting Override twice. A small window will appear. Click OK to keep old material as sub-material. Now, you have new type of material applied.

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3. Advanced Lighting Override Material only added radiosity properties to base material. In Advanced Lighting Override Material rollout, there are several parameters. We can set Reflectance (how much light is reflected from an object, usually we set brightness of a material using this values), Color Bleed (how much color is spilled onto other objects) and Transmittance (how much light is transmit into object, usually applied for transparent material). What we will change in this rollout is Luminance values. Luminance is used when we want to create glowing effects, like light bulb, glowing monitor screen or neon effects. Set Luminance values to 500-1000.

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4. Now, we need to edit the base material. Click button right next to Base Material. In Blinn Basic Parameters rollout, change Diffuse and Ambient color to any color you want. Activate Self Illumination and drag color from Diffuce to Self Illumination to create a color copy.

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5. When you finished, open Radiosity window (press F10 and click tab Advanced Lighting). You need to re-calculate Radiosity solution again. Click Reset All and click Start. Finally, click Render. Finished file can be downloaded here (zipped, 135kb, 3dsmax8 format)

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