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Final Render 101: Basic HDRI and Ray Tracing

By Stephen Reb
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Date Added: 6th February 2007
Software used:
3ds Max
Although acceptable global illumination results may be obtained by using the environment color as your basis for lighting a scene, using a solid color, or even a gradient map will still produce only a uniform distribution of light.

The more I use HDRI the more I prefer it to other methods of GI. HDRI stands for High Dynamic Range Imaging. It uses 360 degree photos taken from a reflective sphere, a series of pictures with different exposure settings that capture the ratio between dark and bright regions as represented in the real world.Mapped as a spherical environment, HDRI illuminates the scene with different levels and colors of light based on pixel information. The result is more realistic than other methods of generating global illumination, and the amount of light can be altered through the exposure settings.

Final Render ships with one .hdr file, outside.hdr. You can download other HDRI files from Paul E. Debevec's site.http://www.debevec.org/~debevec/Research/HDR/

1. Create a ground plane and two spheres. For the ground I used the grydirt1.jpg included with Max. For the sphere materials I used a specular level of 74 with the glossiness level set at 60.

As with the previous excercise we need an omni light. Its' inclusion in the scene disables Max's default lighting. We want it to show the hightlights on the spheres but not wash out the scene, so turn off diffuse in the modifier panel. Leave specular on.

670_tid_coordinates.jpg
2. Go to the Environment panel and select bitmap HDR from the map browser. Go to Material Editor, then to the Map Browser. Choose Browse from Scene and bring an instance of the map to the Material Editor.

670_tid_environ-hdr.jpg
Under the bitmap parameters assign an hdr file. In this case I used the campus_probe.hdr from Paul E. Debevec's site. The ouside.hdr file should work just as well, though you may have to use different exposure settings.

670_tid_mapbrowser.jpg
Under the Material Editor Coordinates rollout choose Sperical Environment.

670_tid_coordinates.jpg
Under the Bitmap Parameters change the RGB Channel Output from RGB to HDR. Below that are the exposure settings. I chose -2 for this tutorial. Play around with the setting and see how they affect your scene lighting.

670_tid_hdrsettings.jpg
Make sure your object properties are set to recieve and generate GI. In the Material Editor, under the Caustics and Global Illumination rollout, check both receive and generate. Set their values to 1.0.

In the Final Render Globals dialogue set a 1/1 prepass size and 300 RH-Rays. Render the scene and you should have something similar to this.

670_tid_render-a.jpg
3. This first relase of Final Render doesn't allow the use of standard Max raytrace materials, but they really aren't needed. Final Renders' raytrace options are so extensive that, for many purposes, you may abandon standard ray tracing altogether. The conversion of Standard Materials is imade easy with the FR Material Converter, accessed through the Utilities panel. Raytrace materials won't show up, so new FR materials will have to be created manually.

Open the Material Editor and select one of your sphere materials. For both sphere materials set the reflection level to 3.0. To see how blurred reflections work, open Advanced Controls for one of the materials and check Blurred Reflections/Refractions. Set the amount to .7 and render.

670_tid_raytrace.jpg
But what GI test render would be complete without chrome or a teapot?

670_tid_render-b.jpg
I resisted the urge to include a teapot, but placed a chamfer box behind the spheres. To make a decent chrome start with an FR material with a Blinn shader. Under the Blinn Basic Paramenters set the ambient and diffuse colors to black, and the specular to white, or near white. Under the Final Render Parameters rollout set the filters for both reflections and refractions to white. Change the Reflection Level to 100 and render.

670_tid_render-c.jpg

 
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