Making emissive surfaces invisible in the render while keeping the light

gibrril_fa945a6cee

Hi all!

A while ago I posted a thread here asking how to keep the lighting of an emissive surface in a render, but make the emissive surface itself invisible in that render. The fine folks here pointed out that if you set the cutout opacity value of that emissive surface very low, the surface will keep emitting its light, but will become invisible in the render. Setting it to absolute zero will however also kill of the emissive lighting. Now this tip worked brilliantly up until today. When dialing down the cutout opacity of my emissive surfaces, also the light they emit gets weaker and weaker, where as before today, when doing this, only the opacity of the surface would be dialed don, the emitted light would stay at full strength... I do want the light, but I don't want all the surfaces in my scene ceeating that light... Why can't it work like it used to? I have not updated Daz, nor Windows, nor the Nvidia drivers... Why is the Daz Studio behaviour changing like this? It did the same thing on memory usage while batch rendering an image series... We could do without "silent updates" that actually make things worse, where ever they are coming from...

Thanks a lot,

Me

scorpio

I think you may have done something else to the surfaces, emissives with very low opacity are still working correctly for me.

gibrril_fa945a6cee

Thanks for the reply! I just loaded the lighting set and set the cutout opacity value to 0.000001 instead of 1. As a result the light also "dies" off... Has never happened before...

Thanks a lot,

Me

ebergerly

I get the same thing. I'm using 4.9.4.177. Below are the identical scene, first with the emissive plane at 100% opacity, the second with 0.0001 opacity. I think that's clear indication that the emissive value is dropping with opacity.  

ebergerly

And by the way, DAZ PLEASE just give us a check box to make an emissive invisible in preview and/or render. PLEASE. 

gibrril_fa945a6cee

Thanks for confirming! I was still trying to get it to work here, but it still fades with opacity... Your suggestion for the check box is totally seconded!!! :) My scene is currently filled up with emissive surfaces that light it brilliantly, but totally ruin the look of the scene obviously...

scorpio

I just checked DS 4.10

And you are correct there is a difference in the light produced, I'm not seeing it as pronounced as ebergerly but that might simple be do with different luminance values.

gibrril_fa945a6cee

Hi! I tried "correcting" this issue by changing the luminance value too, but at least for me, it seems impossible to recreate the lighting at 1.0 opacity using luminance as a correcting paramater... I see obvious differences from luminance value of 50.00 and above... As mentioned before, I did not have this issue before today... And I also did not have a memory issue doing image series renders before two days, but that went South too... Did Daz change their software, or did Iray?

Thanks a lot,

Me

ebergerly

I don't think it's a software change since I'm using an old version and it's a problem. Unless they fixed it in a newer version, then broke it again in a newer newer version. 

Richard Haseltine

Don't forget that most surfaces are at least slightly shiny, and so will show a reflection of the light source if it is visible which will go when the source is near-transparent. Try running the test with a matt surface and see how that compares.

ebergerly

Good point Richard. I re-did the test after I stripped out everything on the floor texture except for a diffuse gray (there was a top coat I forgot to remove), and here's the results. Seems like it still points to a decrease in emissive with opacity. 

gibrril_fa945a6cee

Hi again!

It would appear, that as far as I can test, the differences are a lot bigger when the lightsource is very close to the objects: I'm trying to light an indoor scene now and the results are very, very poor. But when I do the same on an outside scene, where the scale of my (identical) light setup is a lot bigger, and the emissive surfaces are a lot further away from the objects in my scene (but they're a lot bigger too), the loss of light is a lot less... Could that be a hint as to how to solve this issue?

Thanks a lot,

Me

ebergerly

gibrril_fa945a6cee said:

Hi again!

It would appear, that as far as I can test, the differences are a lot bigger when the lightsource is very close to the objects:

That would make sense...the intensity of light falls very quickly the further away you are from the source (by the square of distance), so it makes sense that the effect drops as the light source moves away. But the real test is if it happens without changing distance. And it appears it does...

gibrril_fa945a6cee

I see. Now I'm pretty pleased with the results of my outside scene, so can I for instance setup the surfaces of the room my scene is set in right now, to not block light from emissive surfaces? If this would be possible, I could scale my emissive light setup up and hopefully have the same result. yet to get a realistic look through the windows of the room, I have an HDRI light map set up too. The light that comes from that map should still be blocked by the floor, walls and ceiling of the room... Is such a setup possible?

Thanks a lot,

Me

ebergerly

BTW, the other super annoying thing about the use of cutout opacity to make the emissives invisible is evident if you look at my last post, with the setting of 0.0001. Even with such a small value you can see fireflys where the "invisible" emissive is. Very annoying. Yeah, I'm sure there are other settings which might fix that, but what's really needed is a simple checkbox. 

gibrril_fa945a6cee

At least in my outside scenes the light from the HDRI map looks like it's successfully masking these fireflies for me. I use emissive surfaces to soften the hard look of the HDRI map and to make certain surfaces shine more. Yet that effect is very easlily undone in an inside scene where I have to put the emissive surfaces really close to the objects... We do need a checkbox and if at all possible, we need it as soon as yesterday :).

Thanks a lot,

Me

TomDowd

(duplicate post)

TomDowd

I just ran some tests on my own and discovered something interesting. If you are setting the Cut-Out Opacity by any method (setting it to 0.000001 or by loading a black texture) the Thin Walled setting (ON/OFF) has a huge impact. See my tests below. (Note that I use a 32x32 black square for Cut-Out Opacity. A quick test shows that setting to 0.00001 had a similar result.) What you'll note is that turning OFF Thin Walled not only radicially affected the render time but affected the light disperal of the light if Cut-Out Opactiy was in use. 

gibrril_fa945a6cee

Thanks for that!!! I'm still running a batch render now, but I will try out the thin wall setting trick asap!!!

Thanks a lot, Me

NorthOf45

Um-m, have you seen the Ghost Light products from KindredArts? They do exactly what you are looking for. It is not just tweaking settings, they modify the basic shader to make the emissive surface invisible while not affecting the intensity of the light.

gibrril_fa945a6cee

I might look into these too. But the lights I have right now, light the scene just right. I would prefer making these invisible instead of adding new ones that I have to tweak all over, if that is at all possible.

Thanks a lot,

Me

scorpio

NorthOf45 said:

Um-m, have you seen the Ghost Light products from KindredArts? They do exactly what you are looking for. It is not just tweaking settings, they modify the basic shader to make the emissive surface invisible while not affecting the intensity of the light.

The ghost lights have the same problem - its what I use and what I tested with; when visable they are brighter than when invisible.

Richard Haseltine

gibrril_fa945a6cee said:

Hi again!

It would appear, that as far as I can test, the differences are a lot bigger when the lightsource is very close to the objects: I'm trying to light an indoor scene now and the results are very, very poor. But when I do the same on an outside scene, where the scale of my (identical) light setup is a lot bigger, and the emissive surfaces are a lot further away from the objects in my scene (but they're a lot bigger too), the loss of light is a lot less... Could that be a hint as to how to solve this issue?

Thanks a lot,

Me

How gloxssy is the light plane? I haven't tested this, but ti may well be that (if the floor iss till bouncing light off it) that the plane then bounbces the light back down and so adds more illumination, while the new-transparent plane will allow most of the light to pass through.

NorthOf45

I was going to say something similar. I tried a test scene with a Ghost Light and rendered varying opacity by factors of 10 from default (0.0000001) up to 1.0. There is virtually no difference until you start to see the light plane at around 0.0001. Even with opacity at 0.1, the extra light is barely perceptible, and a reflection starts to show. At 1.0, the reflection is obvious, but the overall illumination is still basically the same, with some added reflected light.

So, ebergerly, you are on the right track, just drop the opacity even more. Maybe it is that simple.

But, as a ghost light, why would you ever want it visible, anyway?

 

TomDowd

TomDowd said:

I just ran some tests on my own and discovered something interesting. If you are setting the Cut-Out Opacity by any method (setting it to 0.000001 or by loading a black texture) the Thin Walled setting (ON/OFF) has a huge impact. See my tests below. (Note that I use a 32x32 black square for Cut-Out Opacity. A quick test shows that setting to 0.00001 had a similar result.) What you'll note is that turning OFF Thin Walled not only radicially affected the render time but affected the light disperal of the light if Cut-Out Opactiy was in use. 

Ran a test with an emissive-only scene, multiple sources. With Thin Walled ON the scene rendered in 7 minutes and 38 seconds. With it OFF, 6 minutes and 17 seconds.

TD

gibrril_fa945a6cee

Hi all! I've attached some images to clarify what I mean: I tried creating a ghost light, but eventhough I used the exact same light emitting values that my original light uses and an identical position, the differences are huge. I tried "compensating using the thin wall trick, but it doesn't help.

The "ShineOldLight" screenshot shows how it looks using the old lighting. The "ShineNOK" screenshot shows what happens if the opacity gets close to zero. Can anybody help me to recreate that original shine using an invisible light? The overal lighting stays the same, but the reflection on the surfaces goes away... I can't have that... I need it back :) Thanks a lot,

Me

agent unawares

Okay, that's bizarre.

gibrril_fa945a6cee

I know... The only difference is that the original light uses the Iray Uber base shader and a ghopst light would be transparant... So what surface setting of the uber shader could be causing that shine? If I can figure that out, then maybe it's just a matter of boosting that up to very high level to compensate for the transparancy.

Thanks a lot,

Me

Tobor

A point light, set to a flat rectangle and enlarged to the size of a mesh plane, will produce similar light, and point sources provide a way to hide the emitter (works only on direct light, though, not reflected light or light passing through a transparent/translucent mesh).

The 0.0001 trick works (or worked, if there was indeed a change) because of the way the Iray Uber shader works. It contains many If/Then tests that turn features on and off depending on a source value. As I recall, if Cutout Opacity is 0, the Add Geometry block is skipped, and therefore, there's no geometry from which to base a mesh for lighting.

I don't have or use the 4.9 release versions, but I know other shader settings can affect the light output. For efficiency, you don't really want a glossy surface from a mesh light anyway -- that can slow down rendering. In general, you don't really want to use the default iray shader (for a standard non-emissive object). You always want to apply an Emissive shader first, then tweak it. This sets the proper values of all the nodes for best efficiency and output.

As noted above, the thin Walled and Thin Film settings have an impact, as well as the refraction settings. For that matter, you can hide the mesh by setting its refraction index and weight). See the following very old discussion I started on this topic; this was written during the time of the 4.8 beta, and the steps may no longer be valid for 4.9 release and later betas.

https://www.daz3d.com/forums/discussion/62526/quick-howto-making-mesh-lights-invisible-to-the-camera

gibrril_fa945a6cee

Thanks for the reply! When I reduce opacity, I never put it to zero, but always 0.0001 or something of that nature. But even when I put opacity to 0.5 I can allready see a significant reduction of "shine"... Maybe the uber schader should not be used, but it does give me the desired outcome. If only I could make that light invisible now...

Thanks a lot,

Me

Richard Haseltine

gibrril_fa945a6cee said:

Hi all! I've attached some images to clarify what I mean: I tried creating a ghost light, but eventhough I used the exact same light emitting values that my original light uses and an identical position, the differences are huge. I tried "compensating using the thin wall trick, but it doesn't help.

The "ShineOldLight" screenshot shows how it looks using the old lighting. The "ShineNOK" screenshot shows what happens if the opacity gets close to zero. Can anybody help me to recreate that original shine using an invisible light? The overal lighting stays the same, but the reflection on the surfaces goes away... I can't have that... I need it back :) Thanks a lot,

Me

You look to have very shiny skin there, the bright areas are reflections of the non-hidden light