Image based lighting using High Dynamic Range Images (HDRI) has become a staple lighting method in the visualization arena. The idea behind this method is simple but brilliant. Capture a 360 degree view of the real world and use it to light your CG scene. As a result, you get accurate global lighting that virtual lights can seldom match. It can even be used as an approximation for global illumination, since it lights the scene from all possible directions.
But for capturing light data from the real world, a simple jpeg panorama won’t do. For this purpose we need high dynamic range images. File formats such as .hdr and .exr are the popular ones for storing HDRI data. These images are 32-bit per channel compared to the 8-bit per channel for standard jpegs. This allows them to store exponentially more information about the light, color and intensity captured by a camera. These values then act as just like light multipliers during calculation.
Therefore, our image now truly knows the huge differences in brightness, like the one between the sun and the sky. You can view these hidden pixels by opening an HDRI in Adobe Photoshop and sliding its exposure value left and right. You’ll notice that the image has data from varying levels of exposure. And this is exactly how HDRI are created as well, by shooting panoramic photos at different exposures, and combining them.
To get started with learning how to light your scene with HDRI, you’ll need a sky HDRI map to follow along. Luckily, one the best makers of sky HDRI maps, Peter Guthrie, has made available an excellent map for free. You can download it from here.
Lighting with HDRI
To light the scene in 3ds max, follow these steps:
- Create a new VRay Dome light in your scene. Make sure its multiplier is set to 1.0.
- Add a new VRayHDRI map in the texture slot of the dome light. By default the dome light is set to use only the upper hemisphere of the map, which is perfect for skies. This map input has been specifically designed for use with HDRI files.
- Create an instance of this VRayHDRI map and load the downloaded sky map through the bitmap slot. The mapping should be spherical by default.
- Don’t worry if the map looks completely white. This is due to an overexposed preview. You can correct this by setting the Overall mult. to 0.1 and the Render mult. to 10.
- To view this map applied in your viewport, plug it into the background environment map window, and change your viewport background to the environment map option.
- You can also change the direction of the sun through the Horiz. rotation spinner of the map. This change will be visible in your viewport.
- Lastly, not all HDRI have the same level of dynamic range. This means the sun might not be that intense so as to cast strong shadows. To make our HDRI cast shadows to our liking, we can tweak the inverse game setting.
- The inverse gamma setting in the VRayHDRI map controls the gamma function of our image. Values lower than 1.0 boost the contrast of our sky map, making our bright sun even brighter, causing it to cast stronger shadows.
- A value of 0.70-0.75 works best for maps created by Peter Guthrie.
Moreover, you are able to use the beautiful skies as your background as well. Most of the quality sky HDRIs are of very high resolutions, so you won’t have any problems with pixelation when used as background.
I hope you found this tutorial helpful.
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