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Raziel
06-15-2002, 08:38 PM
Hi all,

Can someone explain what HDRI is, and how to use it in LW?


Thanks in advance

leigh
06-18-2002, 11:09 AM
HDRI stands for High Dynamic Range Image, and basically these are images that contain information beyond the spectrum of regular RGB images. In other words they have values higher than white.

You can use them, in conjunction with radiosity, to light your scenes. In Lightwave, you do this by loading the HDR image into your Image World (go to Scene>Backdrop>Add Environment). You load the image in there, and enter a brightness value depending on how strongly you want the image to illuminate the scene.

The problem with using HDRIs though, is that they are very hit-and-miss. Sometimes they work beautifully, other times they just ruin your scene. In order to work well, your HDRI needs to have been made properly, or else they cause unsightly artifacts when you render. The way in which they are made, is by getting hold of a very reflective ball, and placing it in the environment where you filmed the plates onto which you are going to be compositing yur animation. Then you take photographs of the ball from all around it, so that you end up with a series of photographs reflecting a 360 degree panorama of your environment. Then, you take all these images and compile them using a program like HDRIShop, and you are left with an HDR image.
However, these reflections are often what cause the artifacts. Some people tend to use a plain phong ball, and just take photographs of that, and use that base colour as your radiosity environment.

If you want to read more about them, and download some sample images, you should go here: Recovering High Dynamic Range Radiance Maps From Photographs (http://www.debevec.org/Research/HDR/)

:)

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