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HDRI - High Dynamic Range Image

By Mihai Pocorschi
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Date Added: 9th December 2009
Software used:
3ds Max, V-Ray
832_tid_img001.jpg
Hello and welcome to the english version of HDRI 101.

I tried to detail as much as possible the steps that one has to follow, in order to help the ones with the means, but haven't used them yet. This tutorial is divided in two parts, first one concentrating on V-Ray and the second one on Brazil r/s. I may do a sequel on Final Render but it's highly unlikely (I may do it if there is a request for it, and if Cebas decides to give me a copy of it, as I don't have it or use it).

The tutorial is organized as follows:

1. Intro
1.2. Tech Stuff - Boring stuff for the action type
1.3. The Scene
1.4. Environment And Rendering
1.4.1 Standard Environment
1.4.2 V-Ray Environment
1.4.3 Brazil Environment
1.5. Conclusion

1.1. Intro

First and foremost, go and get Fiat Lux, an incredible short by Paul Debevec. For all those that didn't see it, the subject is the schism between Galileo Galilei and the church, and from a technological point of view what stands out is the recreation of St Peter's Basilicum in 3D, introducing some artificial objects there, dynamics simulations on them and rendering all with a technique called Image Based Lighting - IBL in short.

You can download the movie in MPEG-1 format from: www.Pocketmovies.net.In the forementioned movie you will see HDRI being used extensively. But what's that? HDRI = High Dynamic Range Images. Yeah? And what are those? See next section for an explanation. And you probably should visit Mr Debevec's site also. It's www.debevec.com, and it's a great inspirational link.

1.2. Tech Stuff - Boring stuff for the action type

There are two types of images. Low Dynamic Range Image(LDRI) and High Dynamic Range Image(HDRI).

The first one comprises "normal" bitmaps [like JPEG, TIFF, BMP...], bitmaps which have 8 bits per pixel, with values between 0-255 [in RGB mode]. Which means that there are only 256 levels of luminosity, which doesn't cover by far the range that can be captured by a camera, with different levels of exposure.

On the other side we find HDRI, whose values can get a lot higher then 256. The main feature is that the value of each pixel is proportional with the quantity of light on each pixel. Basicaly, instead of just storing colors on the screen like normal bitmaps do, the HDR format sotres the quantity of light per pixel.

1.3. "Prepping"


1.3.0 First things first (or: things that you must know or have)

  • Brazil r/s
  • V-Ray
  • HDRI Import plugin (3D Studio Max doesn't know how to use floating point images), as it is the case with the HDR format, so you will need HDRI.bmi, a free I/O plugin from the good folks at Splutterfish.
  • HDRI Files (try Mr Debevec's site or get the one i used in this tutorial here - rnl_probe.zip)
  • HDR Shop - software for modyfing HDR files. Get it at: www.debevec.org/HDRShop

1.3.1. The Scene

832_tid_img003.jpg
A typical scene for the regual GI addict MUST contain some spheres (if not spheres, at least some cubes :) )

Ok. Now let's create a simple scene. A Stand and a sphere. Now let's add some objects to make it a little more complicated. You guessed it: some more spheres ;)

I'll leave the texturing to you. I made the main sphere out of dark marble, the stand lighter marble, and the rest of the the spheres are glass, different colors of it. At the end i decided to throw in a gold teapot, just to test some metal materials.

For this tutorial I used rnl_probe.hdr (you can find it in this archive rnl_probe.zip). It's a very nice forest, a little dark for my taste but it will do.



1.3.2. Modifying the HDR file

Open HDRShop.

File > Open

and select rnl_probe.hrd (figure on the left)

832_tid_img004.jpg
Image > Panorama > Panoramic Transformation

At Source Image under Format select Light Probe(Angular Map) and at Destination Image under Format select Latitude/Logitude. The rest of the settings are left default. Now you have a usable HDR you can import in Max.

832_tid_img005.jpg
File > Save As...

select Radiance Format and save the new image under a different name. I just named it padure.hdr. (Below)

832_tid_img006.jpg
...proceed to page two to learn more...



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