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'Old school' HDRI lighting in Iray

Journal Entry: Mon Mar 30, 2015, 10:37 PM


updated: 3/30
currently: experimenting


Hookay...I'm going to try and explain some stuff I learned about HDRI files and using them with DAZ Studio 4.8's Iray renderer. You may already know some of this, but I'm hoping it will help some new users (and veterans like me who still may never have learned it).   :)


Here's an example of the kind of HDRI image that I've used in my testing, a spherical one that's twice as wide as it is high. The one I used was 2000x1000 and was only grayscale though, and I'll explain why in a minute.

macsix.deviantart.com/art/Anvi…

Now the thing I didn't know until today is how HDRI maps like this get positioned in relation to your scene. Try imagining that image divided into four equal horizontal chunks, like this:

  [] [] [] []

From left to right, the chunks represent forward (-z), right, back (+z), and left; basically rotating clockwise around the center of your scene. In that example, you can see that the sun is placed in the first chunk. That means that when this HDRI is placed in your Environment Map slider (in the Environment tab of the Render Settings panel) and your Dome (or box) Rotation is set to 0 (default), the sun will be positioned directly in the background of your scene (when viewed straight on with a Front View camera or so).

Moving the sun, or whatever the light source is, can be easily done by rotating the dome. For every 90 degrees you rotate the dome, the sun will move to one of the four sides. If you want this HDRI's sun on the right side, set the rotation to 90 degrees. For a sun facing the scene, use 180, for a sun from the left side, use 270. 360 will move the sun all the way back to where it started (as will 0), and of course you can use any value to position the sun, not just those four primary values.

If you want to actually see the dome and the applied map while you rotate it, make sure you're using a Finite Dome, try setting the Dome Scale Multiplier to something like 3.50 or 4.00 and turn Draw Dome on.



HDRIs can cast shadows, but many don't create very noticeable directional ones. I made a crude one for my tests that was very useful in helping me understand how they work, and you can download it here: sta.sh/0641i6ifdym. Convert to a TIFF, HDR, or EXR if you like, although it is only meant as a light-casting map and not any sort of background or environment substitute. It doesn't warp like a real HDRI should, so don't render your dome in the scene when using this.

Now you'll notice that it's really simple - just a single bright spot on a dark gray background. It's also centered, which I primarily did because I couldn't wrap the gradient light from one side to the other, but it will also cast light and shadows from the right side of the scene without you having to use any dome rotation (as the light is in that second 'chunk'). This sort of HDRI has two simple functions: it casts a single light that will generate directional shadows (similar to a Distant Light), and will generate slight global lighting throughout the scene because the rest of the image is not solid black (somewhat similar to Age of Armour's Advanced Ambient Light). You may need to either turn the Environment Intensity up to 3.000 or lower your Exposure Value in the Tone Mapping section to something like 11 or 12 to get it bright enough depending on your scene.

This sort of HDRI and real ones that are mostly grayscale with large light and dark areas are very useful for getting environmental lighting that more closely simulate 3Delight renders and not the photorealistic 'cold' lighting that Iray and other PBR renderers can give.


updated: Here are some very good HDRIs that were the original inspiration for my experiments:

HDRi Pack 1

Be sure to get his other sets too.


And here is an example of a 3Delight render and an Iray render using the sample HDRI I made:

Iray Papa Comparison (updated) by SnowSultan


I hope at the very least that this might give you a few new ideas for using lighting and HDRIs in Iray, and perhaps make lighting a little less frustrating while we all learn this powerful but complex new rendering system. 3Delight may be better for fantasy and non-realistic renders by default, but I'd still like to take advantage of Iray's features while keeping my general artistic style. Hopefully for the time being at least, this may be a way for us to do both.

Thanks for reading!


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:icon0snow-white0:
0Snow-White0 Featured By Owner Apr 1, 2015  Hobbyist Digital Artist
Thank you for the tips, SnowS! I will reread everything more calmly later. It´s been two days that I don´t open DAZ, because i have been a little busy these days. You have any idea when they will release the official version? I'm kind of tired to just make tests ... lol I wanted to make a more complex image. But I´m waiting.
And I brought a new game too (DA:inquisition) . So, you know, when we have a new game we spent some time away ... lol or at least in the first days. :D

PS: I love those HDR packs! :)
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:iconsnowsultan:
SnowSultan Featured By Owner Apr 1, 2015   Digital Artist
I wish I knew when we were getting the official version, but these days I don't know anything that the public doesn't know when it comes to DAZ. There have been a lot of private updates to the beta though, so we might get a new one fairly soon.

Oh, that Dragon Age is supposedly really good! I was in the minority because I hated the first two, but people say Inquisition is a big improvement. Have fun and take a break from 3D for a little bit.   :)
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:iconippotamus:
Ippotamus Featured By Owner Mar 31, 2015
Aren't those packs incredible?  I like pack #2 especially.  Basically a studio light set in a dome.  :)
I did not know about the finite dome settings.  I will have to try those out today.
Thanks so much!
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:iconsnowsultan:
SnowSultan Featured By Owner Mar 31, 2015   Digital Artist
Yeah, those really helped me to understand how HDRI work and that they actually can be used artistically as well as realistically. I've gotten some odd results scaling the dome down, but hopefully those numbers will allow you to see it and get a better idea of where the HDRI lighting is coming from. Thanks for taking a look!
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:iconkismet2012:
Kismet2012 Featured By Owner Mar 31, 2015
Thank you for this.  I have been totally frustrated trying to figure out HDRI lighting in Iray.
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:iconsnowsultan:
SnowSultan Featured By Owner Mar 31, 2015   Digital Artist
No problem, I hope it can be useful.  :)
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:iconchestermorton:
ChesterMorton Featured By Owner Mar 31, 2015
Very interesting, looking forward to trying these things out.  Thanks!
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:iconsnowsultan:
SnowSultan Featured By Owner Mar 31, 2015   Digital Artist
You're welcome, I hope it helps!
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