WTH is HDRI and why will i want to use it ?

I just visited http://www.debevec.org/Probes/ to try and understand what HDRI is and its importance and frankly the stuff there just makes my brain hurt. icon_frown.gif

Can anybody take pity, and break it down for me as simply as possible. Sort of an “Idiots guide to HDRI” icon_biggrin.gif

Thnx.

while im sure im not the best person to explain it, i know that it has something to do with lighting a scene using an image. The image controls the brightness and color of the light and can yeild very realistic results (not to be confused with “omg tahts sososooo fotorealiztic mate bhow did you do that thats sooooooooooo good!!!1111oneoneoneone”. you can usually spot this type of ‘fotorealistic’ art by its rediculously excessive use of AO and depth of feild effects.)

HDRI is a high tech way to light your scene that will usually increase your render times exponentialy. I dont believe ive ever seen it used for much more than novelty.

HDRI stands for “High Dynamic Range Imaging”, and it basiclly means that an HDRI image can represent light brightnesses that are brighter than the brightest value your monitor can display. It also means that they just generally have higher accuracy, since they aren’t limited to the 256 values per channel that most image formats are limited to.

HDRI images are useful for lighting 3D scenes (usually as a sky texture) because they are capable of representing a much, much, much larger range of brightnesses (with higher accuracy) than normal images can.

Let me give an example. Let’s say you have picture of a bright sunny day that you want to use to light your scene with. There is no way that you can accurately represent the brightness of the sun in the image, because it is so much brighter than everything else in the picture. A normal image will typically just represent such brightness as the brightest white the monitor can display. But that’s still no where near the brightness of the sun. If you were to light your scene with that image, you would certainly end up with lighting that’s too dim and diffuse.
If, however, you use an HDRI image, the brightness of the sun would be accurately represented as many many times the brightness of the brightest white the monitor can display, and thus the lighting in of the 3d scene would be more accurate.

Obviously, HDRI images aren’t useful for pictures you just want to look at (the monitor isn’t capable of displaying them correctly anyway), but they are very useful for image-based lighting.

Hope this helped!

How would I be able to do this? Can it be done in blender?

Yes, you can do it in Blender using Yafray. It’s simple. Download a .hdr probe,
some are at http://www.devevec.org/Probes and more can be found with google. Go into the world settings ( F8 ) and on the right add a new texture, click the angmar button and go into the texture buttons (F6). Load the .hdr file and render it in Yafray using GI full or SkyDome.

As for the matter of “why use it”. Here’s a comparison, the only change made was one time I used HDRI the other I didn’t.

With HDRI:

http://img2.exs.cx/img2/687/with.jpg

Without HDRI:

http://img2.exs.cx/img2/5739/without.jpg

I think you can tell which is better. And lol, that was my first time using HDRI and I will be using it a lot more.

That is not really a good example of HDRI, for this kind of render it is almost no different from using an environment map in Blender. For some reason some people seem to associate HDRI with reflections or something like that, you can do that just as well with regular images and normal raytracing, no GI needed.

Thnx guys. Afew tihings have fallen in place. I will be reading any further post and will ask questions later during the week as i practice. :slight_smile:

A good tutorial :
http://biorust.com/index.php?page=tutorial_detail&tutid=73

Jean

It is used a lot in movie special effects to match CGI and real footage. A HDRI probe is taken on set and is used to light the CG models. That way their color and lighting fits exactly into the scene.

Moreover, as explained on Debevec’s site it makes reflections on plastic surfaces and motion blur a lot more realistic.