Hey all,
I am doing an image for the Master & Servant contest at cg talk but I need some advice regarding volumetric lighting from carrara users. I want light streaming into the church thru the stained glass windows. Right now I get a nice effect having the stained glass tmap in the transparency/color channels which produces the colored light on the floor and walls. I now want to add the streaming light cone in carrara for the streaming volumetric light. The light cones and transparency/alpha channels dont work together.
So,I was wanting to render the light cone creating the streaming light effect as a separate layer and composite it with this image . I figured this was the best way , does anyone know how to do this , it would be appreciated if you can help me out. I guess I could do this in postwork which is allowed but it would be nice to produce as much in carrara as possible.

Message edited on: 04/17/2005 19:53

Here is the image of the wip, I posted it in the carrara gallery too.

It is possible to get colored light cones if you use a gel in the light. I'm not sure how you'd get the light to match up the "gels" in your windows but you could get rid of your windows altogether and let the gell manage the whole thing. I think you should also turn on your soft shadows. -Kix

-Kix

Mike, put the stained glass texture as a gel in your light. Then under light cone, check "use gel" in the fog area. the hard part is getting it to match the window opening.

Patrick

Kixum, I guess I could do it this way then composite back in the stained glass windows. I will look into this thanks. I will turn on the soft shadows for the final render.

Thanks Patrick, I will try this and see how it goes.

Patrick and I are essentially saying the same thing. It should work fine. Just turn off casting shadows with the window pane. -Kix

-Kix

Now I know what streaming volumetric light is. I just thought of it as the dust in the air reflecting the light particles. :) Or are those photons?

This turned out to be kind of fun to figure out but was also not so easy. I built the scene with a floor, a wall, and another wall with the square hole. I added a ball for fun. I then added the window plane and put a map into the transparency mixed with a little black just to make the "blank" part of the image not completely blank. I took the smiley face map and added a big extra border around the edge and blurred it. This became the gel for the spotlight that I used. I turned on the light cone and selected the use of the gel in the fog and turned on the shadows option so that the window frame would cut through the cone appropriately. I also turned on the soft shadows. I turned off the "cast shadows" option for the window pane. I then rendered one image with the gel option enabled and then one with it disabled. I had to do this because the smiley gel is projected in the light cone even before it hits the window pane. I then combined the images in paint shop pro and masked out the part behind the smiley face (to the left, outside) to show the light cone without the gel option. The gel on the spotlight is blurred to be consistent with the soft shadows. Not an amazing example but a functional one AND it can be done (just not easily)! -Kix

-Kix

I've thought about this before. I found a way that works, except that you must use a spot light and that produces a cone instead of a straight beam. I tried to work around by pulling the light way back and narrowing the beam, but that didn't help much. It would be nice if Carrara had a straight square beam like Bryce (which I haven't used in years. Also the light has to be perpendicular to the window, altough I think I may be able to get around that. This is a straight Carrara render, no post. It's late and I'll describe how I did it tomorrow.

My two cents: a straight beam is definitely preferable, since light from the sun would not produce a discernable cone. This is probably obvious to most of you, but someone reading this thread who is new to 3D might not have given the issue much thought.

Thanks for all the tips and ideas,Patrick I look forward to your process . Kixum, I like the fact the light rays are straight in your image. When I get back to doing this , I will definitely look at these ideas. On another note , the final image is going to be very large, the smallest dimension is supposed to be something like 2600 pixels. So this is going to make for a very big image , so come render time for the light cone, is there a way to render just the light cone effect to make things go quicker, then composite the light cone layer and the background scene together.

Attached Link: http://www.renderosity.com/viewed.ez?galleryid=445205&Start=19&Artist=Kixum&ByArtist=Yes

If you look at this image, the light cones are again done by a spotlight which is 2000 units away. The light cone in the image I provided in message 9 was also done with a spotlight at 25 units away and an angle of three degrees. I could have easily put the light farther away and set it to 1 degree which would naturally straightened the rays even more. As far as rendering the cone separate, I'm not really sure how you'd do that and then mat it in later. I think it would get screwed up with the structures that are behind the cone (it wouldn't match well). If you do figure a way to just do the cone, you should share! -Kix

-Kix

How about rendering the light cone directly on black, then using either the Add or possibly Overlay might do a better job as the blending mode for light cone layer.
It can easily end up being too strong, but if you set the opacity down at the same time as using add, you might get a pretty good effect,
harder to say how to do a very good Gel on whatever objects it is too hit,
but if there's no indirect light, nor any ambient light, then anything the light doesn't hit should turn out completely black. EDIT: Oh yeah, Kixum, by Units do you mean Inches, cms, or what exactly?

Message edited on: 04/20/2005 21:11

I say units because it really doesn't matter what you use in Carrara. I just type in 2000 in the "X" coordinate box. -Kix

-Kix

Actually it does matter. If you open a scene I did using CM, and you use inches, it will open and you'll get the values in inches, which will be different. 2000 inches is 5000 cm (actually slightly more, but just about anyway). So that's quite a difference in units. Especially when dealing with something like this 2000 or 5000 is quite a difference. If you didn't have to care for the way the angle of the light looked, and we were just talking about scale, then it wouldn't matter, but in this particular case it does, so kind of interesting to know whether you use metric or "Ancient British Stuff That Even Britain has Decided to Get Rid of", which I like to call it as I've never heard anything about a name for it.

I think Kix is right here. A "unit" can be an inch, a centimeter, or an Angstrom, or a mile; so long as you don't try to mix them in the same document it doesn't really matter.
The "ancient British stuff etc" are called imperial units.
Not that I think they're especially "regal". :-) Ooops Carrara doesn't do Angstroms. Now there's an oversight!;-)

Message edited on: 04/21/2005 16:10

Sardtok, That is what I was thinking of but didn't know how to go about it.I will try a simple test and see how it goes, using the Add or Overlay(haven't used) is a good idea. Thanks for the idea. I tend to ignore the units, just keep them consistent within the scene.

I understand now. I was only thinking in terms of Carrara space. I never import from other codes so that's why I didn't think of it. I always export to Carrara in amapi. -Kix

-Kix

I think we should request for Carrara to have a parallel light like in Bryce. I can't believe this would be that hard to code. This light is just out of the frame, and can be resized to whatever length and width you like. It would make this situation easier to handle, also good for light through trees, etc with gels. Patrick

Message edited on: 04/22/2005 08:35

Those lights, in combination with a weak light cone with turbulence makes for great lasers. Or at least they did in 3dsmax back when I tested it in junior high (equivalent anyway).

Imperial measures -- What a joke! I was raised in the US in the late 60's and early 70's when the country was trying to convert to the Metric system. I learned the metric system, and nowadays I still find it difficult to think in feet and inches, pounds and ounces and all that. Sometimes my fellow countryfolk are just stupidly stubborn! Thanks for a platform to vent about that! Whew, I feel better. (Awesome ideas about volumetric lighting effects, by the way. Great read in this thread.) - Dex

Sardtok, I was trying it using your method of rendering the light cone on black. So..., I duplicated my file, named it light cone, change all the objects in the scene to a pure black shader, no reflections,glow or anything. Turned ambient light to zero. I then did a render , composited with the colored rendering, it worked but the black areas that were supposed to be pure black or 0,0,0 for the RGB values were like 8,6,6. So when I use "add" as the merge mode I get areas that get brighter when they shouldn't . I could fix this in my image editor by changing the semi black to pure black but it would be nice if it could be all done in Carrara. Any thoughts and thanks for your previous help everyone.