scene from metropolis. need lighting advice

Vampyre · Post by **Vampyre** » Sat Feb 23, 2008 2:39 am

I'm back once again to beg help from those with more wisdom than myself. Right now i'm doing a frame from the movie 'metropolis', which i suppose it kind of funny since i'm using metropolis light transport to do it.

This image is very preliminary, i'm just setting up composition and lighting at the moment, no love to the models yet. The problem i'm having now is trying to figure out how to do the 'energy rings'. I'll post the screencap from the movie since the movie is now public domain so you can compare. What i need is a way to make them semi transparent.

I tried to blend an emitter and a null but all i got was a null. any suggestions on how to achieve this effect? maybe an SSS texture with an ior of 1 and very low scattering with a thin light ring inside the torus? has anyone tried anything like this, advice would be greatly appreciated. I can't even figure out how to do it in post production.

ok , nuff blabbing, here's the pics.

Kram1032 · Post by **Kram1032** » Sat Feb 23, 2008 5:19 am

sorry, the only way to do it currently would be to render it twice, once with and once without rings and then blend the image as needed

You know: Emitters aren't materials.
*ANY* Emitter actually has a black diffuse material, which doesn't reflect (or refract) any light at all.
What you'd need, is a volume emitter, which isn't yet implemented in Indigo.

Vampyre · Post by **Vampyre** » Sat Feb 23, 2008 5:23 am

yeah i was just hoping someone had found a trick to simulate the effect. the problem with rendering it with and without the light rings, is that the image that doesn't have the light rings also wont have their reflections or lighting... so blending the two images would looks odd.

Kram1032 · Post by **Kram1032** » Sat Feb 23, 2008 5:29 am

not necessarily:
if the rings themselves are transparent, their reflections show the same

Vampyre · Post by **Vampyre** » Sat Feb 23, 2008 6:36 am

but they wont be generating light , so the materials that you can see through the rings, will be considerably darker than they would be in the second image, the one with the light rings. when i go to blend the images together wouldn't it look like the materials behind the light rings were darker? its hard to describe what i'm saying.

lemme try again
image 1 = image with transparent diffuse rings
image 2 = image with light rings
image 3=image 2, with image one layered over it using a mask of the rings, so there is transperancy.. right? it seems like anything behind the rings would be too dark in image 1

i'm running a test now with a transparent torus filled with smoke, and a very thin filimant of light. But i think i'll try this method as well , just to see what the results would be.

BbB · Post by **BbB** » Sat Feb 23, 2008 7:00 am

Do as Kram says. It will be much faster and also accurate.

alexmeyer · Post by **alexmeyer** » Sat Feb 23, 2008 7:30 am

Guys? I see what you're saying, and normally that would work fine. But I think Vampyre's point is the those are the *only* light sources in the scene (looks like it anyway). So, you take those out, to get a clean background plate, and no more light sources.

Kram1032 · Post by **Kram1032** » Sat Feb 23, 2008 8:24 am

I know.
Actually I waited for Vampyre to say just that

(or post the bug-message or something)

@ Vampyre:
*If* that's the case - that your rings are the only lightsource,
your current method will be quite the only one, besides using some different transparent or translucent materials, instead of SSS...

Vampyre · Post by **Vampyre** » Sat Feb 23, 2008 10:14 am

they are not the only light source, but they are 5 to 10 times brighter than the others.. and yeah ,that was what i was trying to say. I've been sick with the flu and its messing with my head, sorry for being hard to understand.

the SSS transparent tubes with thin light filaments produced a beautiful image, but it had flaws i didn't want to mess with, plus it would have taken forever. but i think i've found a post pro method that will provide adequate results. rather than blending two images, im just rendering the rings really thin, and then using the gimp to dilate and blur them.. so the edges blur into the image.

BbB: accurate? can floating energy rings be accurate?

I see now what kram means though i think.

alexmeyer · Post by **alexmeyer** » Sat Feb 23, 2008 10:24 am

@Vampyre: That was gonna be my next suggestion, just blur em in post. Glad that' works for you.

Kram1032 · Post by **Kram1032** » Sat Feb 23, 2008 12:30 pm

Ok, problem solved.
At the "accurate" question:
Yes, floating rings can be perfectly accurate.
For example, you can get them to float with magnetism

(though, I guess, it's hard to control...)
and the glowing part isn't all that unrealistic.
The main question is, how they can glow (seemingly) without battery, that intensive and white ^^

Vampyre · Post by **Vampyre** » Sat Feb 23, 2008 1:37 pm

duh, with pixie dust.

actually, if were gonna nerd it up and try to figure this out, i'll have a go at it.

first off, in this scene there are no humans. who's to say the robot isn't in a glass chamber filled with highly pressurized gas of some sort that glows when excited? Or not, i have no clue, im totally talking out of my butt if you havn't guessed..

I did see a video of a completely stunning 3d volumetric display though, that could project (star wars style) holograms in a dense gas chamber... so maybe thats what these are?
http://www.youtube.com/watch?v=GQT0vcw7 ... re=related

Neobloodline · Post by **Neobloodline** » Sat Feb 23, 2008 6:02 pm

You could use Blender3d's internal renderer... I know that won't be popular among the fanbois but it really is a very nice renderer and growing daily. The ring effects and more can be achieved with blenders halo effects. You can make one halo white and small and make another colored halo at 50percent opacity (and play with halo settings) overtop of it and get a very nice glowy look. Also use aprox. ambient occlusion and soft shadows and it would do nicely for your picture.

sth · Post by **sth** » Sat Feb 23, 2008 8:59 pm

once I made strong shadeless white out of pure white diffuse (1.0 1.0 1.0), other materials in the scene I made much darker (i.e. for "red" material I set to 0.07 0.01 0.01), then I made tonemapping much brighter to make very dark image few times brighter. Indirect light was lost, but my white diffuse turned into kind of emitter

Maybe you can try this?

(Of course diffuse doesn't send the light and it's still only reflector so you need to have emitter in the scene)

Vampyre · Post by **Vampyre** » Sun Feb 24, 2008 12:33 am

Neobloodline I considered using blender to do the rings. but even with all its new features in the upcoming version (and it has quite a few nice ones, love the blurred reflections) its still a biased rendering engine. indigo just has a quality about it that is really , really hard to get with other raytracers. for instance, making high res toroid area lights in blender doesn't sound like fun

that being said i did think of using blender to do halos for the rings, and then layering them on the indigo rendered image, but i was concerned that the images would clash.. they wouldn't match up properly color wise.

i will how ever, i think, be using blenders nodes to blur the final rings using a mask.

sth
thats not a bad suggestion, i considered that too, in fact this was my first plan before i decided that just post pro would be the easiest route. since my scene is modeled in blender, using it to do post production with its wonderful node system will be a snap, and my test came out pretty decent.

now i'm on to modeling the robot, adding in the power cables, setting up the composition.

Do u guys think that i have too many rings in my version? should i reduce it to two sets?

scene from metropolis. need lighting advice

scene from metropolis. need lighting advice

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