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HDRI tutorial
2005 copyright cliffhanger visuals http://www.cliffhanger.nl 3D visualisatie 3D illustratie 3D animatie

Introduction

In this tutorial, I won’t go into the technical and physical backgrounds of High Dynamic Range Image. Instead, I’ll present you with a basic instruction about the photography of the images needed to produce HDRI’s, the way to go about inPhotoshop (which in CS2 has a feature incorporated that will produce a so-called Radiance document with little effort) and how to use the HDRI in 3D (I use Cinema4D but other software will differ only slightly) Just a little background though: Did you notice that on a sunny day, your camera tells you that you need 1/30 seconds of exposure with a 2.8 lens opening indoors and when you step outsideit just needs 1/1000 seconds at f11. In fact the difference between complete darkness and complete “lightness” is pretty endless. A camera or your eyes can only see a portion of it without adjusting, and once they have, they can’t see as well anymore what they saw before the adjustment. When you step back inside the house it takes a second to get used to In 3D-software maths, this wide boundary orhigh dynamic range can be inverted to do something special: it can act as an actual light source. the darkness. And when you take a picture with your camera still at 1/1000 at f11, the print is black. In an HDRI, multiple situations are all combined in one image: indoor and outdoor at the same time so to say. You need a slider to make it visible to the eye, but when you do, it is all there: thesphere of the sun and the inside of a drawer.

Ansel Adams

HDRI photography: what do you need?

If you have all of the items above, you’re a rich man: Adobe Photoshop CS2 to convert different camera exposures into a Radiance image, a tripod and a camera that can shoot RAW-images. In this tutorial we’ll use them all. But:

If you can’t shoot RAW, that’s OK. If you don’t have Photoshop CS2,visit http://graphicslab. ict.usc.edu/HDRShop/ to get a free copy of HDRshop v1, which does a good job. It’s only available to the Wintel platform though. They have a lot of fantastic information about the technical side of HDRI, too. And if you don’t have a tripod, you can ask your sister too stand really still for a while. No, I tripod is handy. The item on the right isn’t mandatory either. Ifyou don’t have a professional probe, you can use a christmas ball. But again here, you can work without a perfectly reflecting sphere. (You would use it to get 180 degrees of surrounding environment to encapsulate your 3D scene. In the following example I used simple rectangular images and for me that works just fine. If your scene contains smooth, dome-shaped objects, then you start needing aprobe of some sort as the seams of a rectangular image would be visible.)

HDRI photography

Open a RAW-image into Photoshop and Photoshop will open its RAW-image dialogue. This photo of my studio door is pretty much balanced. You can more or less see what is inside and you sort of see what is outside. There is no pixel information in the highlights though. I check that by activating theHighlight-tickbox: When I do that, Photoshop gives me this feedback:

Pixels that are pure white are displayed as red. As you can see there’s no information in the sky behind the door, nor is there between the blinds. If I want to see that information, I need to bring the exposure down. But when I do that, dark parts in the foto start to become pure black. I can check that by activating theShadows-tickbox: (It is difficult to see -overexposure happens much easier than underexposure- but it’s the blue areas.)

Each of the photographs cover another part of the light situation and the range per photo is quite small. Going from the deepest shadows up to the brightest highlights, in this weather, I need to make about 6 to 7 photographs that I import into Photoshop CS2:

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