Can Iray Make a "Black Glow?"
Vueiy
Posts: 546
So, I've been playing w/ Iray for months now, experimenting w/ the emission function under the surfaces tab, and I was wondering: is there a way to create a black glow of sorts? I'd like certain things to "emit darkness" (so to speak) the way other things can emit light. Mostly, it would have applications for when "bloom" is enabled in the rendering (which, for me, is pretty much all the time), to give things a shadowy effect, instead of them simply appearing flat black. It has occurred to me to render bright lights, then do a negative image in PSP, but that requires several extra steps that I'd like to be able to skip, if possible. If all else fails, I could just postwork it in PSP, but, like I said, it'd be better if I could skip that. I know that currently if the emission color is set to black, it just won't emit anything (which makes sense), but could there possibly be a way to alter that? Any help (even if it's just "Not w/ the current specs of Iray") would be appreciated. Thanks!
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Comments
From what I understand, pure black (0/0/0) in the emmissive channel for an Iray shader is no emmission, so I wonder if you just bump one of those numbers up a tiny bit (like 0/0/0.01 or some such) if that would be enough for Daz to say "Hey, we have light here"
Did you try setting luminance to a negative?
No, I didn't, but that sounds like an interesting thing to try...If it works, I'll post a pic. Thanks for the suggestion!
Iray is a photorealistic renderer. As such, in photoreal mode the algorithms used are based on actual physics. Conditions such as this are often purposefully blocked...because they can cause crashes.
Basically what you are wanting is the emission profile of a black hole...or negative light.
I don't know enough about the internal programming of Iray to say with certainty that it blocked, but from the way Iray handles other things that stretch the bounds of the algorithms, I'm pretty sure it ignores the settings that are 'way out there'.
So...best advice...try in Interactive (not photoreal mode) or stick with 3Delight for this kind of effect.
Negative luminance values will work to "suck out" light from an area, but I wouldn't call it a "glow." Still, it may have the look you're after. For best results, adjust color temperature to 0.
You may instead want to use a very dark blue or some other deep hue. The emission feature is turned on by setting any color other than absolute black. Even a single digit change in the R, G, or B channels will turn it on. Of course, you'll need to experiment with the luminance values, which may have to be turned up so high the value exceeds the use-case expectations of Iray, and causes artifacts or other issues.
Thanks, I got it to work! I'm gonna work on it some more and hopefully have a product up to sell (or maybe as a freebie) in due time.
Huh. You can set luminance negative. Well, how 'bout that!
Many renderers intentionally support this. Poser has for years, and I understand -- though never used it -- Bryce does as well. Don't know about 3DL.
The one weirdness I've encountered is that it doesn't behave well as a ghost light. Not sure why.
It IS pretty cool doing it with fog...
Never tried to hide the negative source, but you could try one of the other techniques to making the mesh less visible, such as playing with the refraction values.
Yea,
contrary to the "normal" ghostlights, here the light sucking efficiency directly depends on the opacity.
But yes, that light sucking effect is quite horrible. The more iterations, the more light it sucks.
The scene's lighting also affects how well it shows up. I got the first step done fairly quickly, but the rest is gonna take a little trial and error...