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View Full Version : No hotspots please.....


Synthesizer
02-23-2005, 08:37 PM
Hi,
I am trying to light a subway station. I need the lighting to be quite diffused and sort of bright, but without any hotspots. I cant use Mental Ray because it is for an animation and i need fast render times (otherwise I would use it). What I am really looking for is a way to get area lights to not have huge hotspots. Even if I set the decay to none, I will still get a really bright spot where the light is close to a surface. Anyone know what to do? Thanks.

This is what I am looking for:
http://fork.uc.org/gallery/albums/metro/2489_G.jpg
http://fork.uc.org/gallery/albums/metro/2515_G.sized.jpg

1armedScissor
02-23-2005, 08:52 PM
At this point you should start to adjust the shaders in your scene.

Synthesizer
02-23-2005, 09:13 PM
How should I adjust the shaders? Lower the diffuse or something?

1armedScissor
02-23-2005, 09:56 PM
The final look of a scene is totally dependent upon the relationship between lights and shaders. You'll want to not only look at the values of your shaders attributes (ie. specular color, color, diffuse, specular rolloff etc), but also the type of shader you're using (blinn, phong, lambert etc), as well as anything that you have mapped to a shaders attribute (for example if you have file textures that you've created connected to the "color" of a particular shader, and if you light this shader in maya with a light source that has little to no intensity and you're texture seems to be "blowing out" or too bright, perhaps you're texture file is too bright). There are a billion and one ways to work/fix problems like these, and a ton of different paramaters. You'll also need to look at your texture file's color balance options. Without alot more information from you (a scene file, renders depicting the problem, a sample hypergraph tree of some shaders you're using etc ). There's not really any way someone can tell you to "do this" and then everything will work perfectly. It can take years for an artist to be able to look at a scene and not only evaluate what problems exist within a scene, but also how to determine the most effective and efficient way to correct problems that exist within a scene. There's a ton of things that could be done to fix your particular problem that I'm sure I've left out too. Is it possible for you to post some renders?

Synthesizer
03-05-2005, 03:09 AM
Hi,
Sorry for the long delay in replying, I missed the email that said you replied.

I have managed to lower it in some spots by lowering the specular colour, but I get hotspots for lamberts too. What my problem is, is I have area lights along a wall, facing away from the wall at about 45 degrees. The area close to the light will be extremely bright, but even just a bit farther away, it will fade out to the level that I want it to. I dont understand this since the light is not set to decay:shrug: I dont have the scene at home right now, but I'll be able to show you a render on Monday. Thanks for your help:)

Stahlberg
03-05-2005, 06:55 AM
There are many things you could try.
1. A negative light, smaller than the original, adjusted to just 'suck' enough light out of the hotspot to make it look better to you.
2. Baked lighting, paint the hotspots darker.
3. Tinkering with the response of the Lambert to the light, in the Diffuse channel. Using a ramp, a clamp and another Lambert you can in effect adjust the Gamma for that shaders' bright areas. (You could use the Ramp Shader, download some cartoon shader, or look at my site for the skin shading tute which has something similar, there are other ways too.)
4. Placing a dark semitransparent sprite over the hotspot (a roundish surface with a transparency ramp, switch shadows off, place it in your 3d scene, a concentric NURBS like the top of a cylinder is the easiest to map in this case).

Jackdeth
03-05-2005, 07:09 AM
Just use a surface_luminance running through a contrast to "key" the hot spot, and then use that to drive a blend_colors node that has you normal shader and a darker version mixed together. Where ever the hotspot is, it will be repaced with the darker shader so it won't ever get too bight. And for more control you can throw a set_ranges into the middle of that. This is also a good trick for skin shaders too.

Stahlberg
03-05-2005, 05:04 PM
Yes cool, that's method number 5. :)
And here's 6:
Map a circular ramp to the spotlight so it's a little darker in the center than everywhere else. Maybe using a volume light with this method might be slightly different result, could be better.
7: Render a mask pass where the spots are grey on black background, then use it in post to tweak brightness.

Synthesizer
03-10-2005, 06:59 PM
Hi,
Thanks for all of those suggestions!

Just use a surface_luminance running through a contrast to "key" the hot spot, and then use that to drive a blend_colors node that has you normal shader and a darker version mixed together. Where ever the hotspot is, it will be repaced with the darker shader so it won't ever get too bight. And for more control you can throw a set_ranges into the middle of that. This is also a good trick for skin shaders too.

Do you think you could perhaps tell me how you connected the surface_luminance to the contrast, and what the contrast settings are. I can only seem to make it have more contrasthttp://cgtalk.com/images/smilies/shrug.gif

Jackdeth
03-10-2005, 08:19 PM
"Surface_lum" into "X" channel of "contrast" which is set to 2.5, which is attached to the "blender value" of a "Blend Node." Then you plug your bright and dark shaders into that blender... and volia!

beaker
03-10-2005, 09:51 PM
Why not light with diffuse only lights(specular turned off). Another thing, this really sounds like you should mess with your materials on your objects so they don't have such strong specular on them.

sporadic
03-11-2005, 02:58 PM
A slightly easier method (I think), which I've had lots of success with is to use a lightInfo node to drive the intensity of the light. Use the distance to the light to drive a SDK which gives the intensity. Using this method, you can simulate any falloff from the light you like. A common one I use is a truncated square falloff, where it follows the normal falloff with the inverse square of the distance, but has a maximum intensity so that when distance is small it doesn't go to infinity.

This works extremely well, and means you don't have to mess with the object shaders.

Synthesizer
03-11-2005, 04:28 PM
LOL! I found out how to do exactly what I wanted. I just put a ramp on the intensity of the light, with no decay. Now all I have to do is change the ramp and I can make my own custom decay. I think I've actually done this before, but I just forgot about it. Its nice to have this big list of other options as well though, thanks everyone:thumbsup:

edit: Wait, that didnt work right, it does the falloff on a per object basis. I suppose this would work if I used one light with this only for the object with the hotspot, then another light for the other objects. What I really want is an intensity curve for area lights.

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03-11-2005, 04:28 PM
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