Realistic lighting (no GI)

[Blooz]

anybody???

[chainsaw]

hi blooz,
why not start by using gi? gi just like photography is based in the physics of real light and if you know how it works I think it might be easier for you to simulate it afterwards.

besides many scenes and most environments it doesnt make sense lighting any other way, you would spend hours trying to get it right, just to start over cause someone wants the sofa a bit to the left.

not to mention its way faster to setup.



http://img19.echo.cx/img19/452/interior5wt.jpg

[Greedo]

I have an awesome tutorial on this kind of thing i read it and will never use GI again. I just need to wait for my uni to update its site so i can access it again. end me your email address to sebastian_fletcher@hotmail.com and i will send it to u.

[jeremybirn]

Why don't you render & post 3 images: just your keylight (the direct sunlight only) then your fill light (all the light from the sky that comes through the window at other angles) then your bounce light (the indirect light motivated by your key and fill bouncing off the walls and furnature.) Then post the final with all those lights visible, but if we could discuss the 3 images one at a time people could give you a lot more feedback, and I think the excercise of looking at and thinking through these three things as separate images will help the next version a great deal. It's OK to use some color in your lights, too, like warmer colored key, cooler fill from the sky, and bounce that gets tinted by the furnature...

-jeremy

[Noc]

whats gi? never heard of it.

[tomhosking]

whats gi? never heard of it.

global illumination, basically diffuse reflection. if you hold a red bit of paper in sunlight next to a white bit of paper, the white paper will get tinted red slightly. its subtle, but it adds a lot of realism to a scene, and a bit of render time as well...

[Blooz]

thanks for the reply guys, here are my attempts at the key, fill and bounce lights

key:
http://img248.echo.cx/img248/4701/key9ip.jpg


fill:
http://img248.echo.cx/img248/6236/fill0un.jpg

and an attempt and bounce:
http://img19.echo.cx/img19/4912/bounce2fw.jpg

here is the final image:
http://img19.echo.cx/img19/7286/composite4ei.jpg

jeremy, i appreciate your help and actually was looking to buy your book about a week ago but my local borders didn't have it, so im ordering it on amazon.
chainsaw, thanks for the reply, i actully do study some GI renders but i also read somewhere that it might not be the best practice and it is best to focus on images or real objects.

[chainsaw]

"...it is best to focus on images or real objects." thats very true and very wise.

now I'll let Jeremy a master of the old school enter ;)

[jeremybirn]

Key - off to a good start. Maybe the sofa by the window needs a rim light to help it look as if it's backlit by the key.

Fill - doesn't look motivated. Only source of fill is the sky outside, but the shadow directions and illumination look like it's coming from a point in the middle of the room. Try more spotlights at different angles from outside. Fill would be more blue than green - there'd be a little green light in your bounce though.

Bounce - Looks blank, uniform. Try adding bounce first back at the window area (window areas always get bright in rooms like that) then up through the floor and back through the bright wall at the other walls, ceiling - aim spotlights with soft edges to keep it brighter in the middle of a wall, a little dimmer in the corners.

I know you're trying to avoid GI and such, but if you can use any kind of occlusion, it'll make your fill and bounce much better. Otherwise, work really hard to darken the corners less exposed to light, if aiming spots doesn't do it them consider some negative volume lights - in Maya a volume light only illums the area within it, you can choose a shape like cylinder and scale it to line a corner, with a negative brightness to darken the corner, and make it not emit diffuse or specular, just ambient, for convincing darkening.

-jeremy

[Greedo]

i recieved quite a few emails about that tutorial it is free on the net at http://www.siggraph.org/education/materials/siggraph_courses/s96_course30.pdf
read the whole thing it is very beneficial

[Blooz]

thanks jeremy, could you elaborate more on how occulsion would help the fill and bounce.

[jeremybirn]

thanks jeremy, could you elaborate more on how occulsion would help the fill and bounce.

When you go into the cracks, like behind the cushion of the sofa on the right, or between the sofa and the right wall, there should be less light. It should be occluded (or blocked) by the objects there. An occlusion shader is one way to get that light blocking. There might be other ways if you aren't using MR with an occlusion shader, you could use lots of soft shadows, final gathering, a dirtmap shader, or cheat in lots of little negative lights to darken each crack.

-jeremy

[lazzhar]

....

Fill - doesn't look motivated. Only source of fill is the sky outside, but the shadow directions and illumination look like it's coming from a point in the middle of the room. Try more spotlights at different angles from outside. Fill would be more blue than green - there'd be a little green light in your bounce though.
.....


A big area light there casting raytraced shadows would add a lot to the render. But the you'll get certainly a slow renderings wich reminds you the GI.

[jeremybirn]

A big area light there casting raytraced shadows would add a lot to the render. But the you'll get certainly a slow renderings wich reminds you the GI.

Yeah, that's where a big area light with no shadows, but an occlusion shader on everything, can sometimes be a safer bet. Blooz sounds as if he doesn't want to use MR or anything advanced though, so he's probably going for some 20th century solution like a fill set-up that's all spotlights - there's nothing wrong with that if you do it right.

-jeremy

[Blooz]

It's not that i dont want to use mental ray or anything advanced, im trying to learn how to light a scene without alot of the advanced techniques (GI) for two reasons. Like I said earlier I read and that lighting without GI can really improve your understanding of how light works and how it effects a scene. The second reason is mainly render time. Alot of the work I am currently doing requires animation within the lit enviroment. I am not necessarily looking for the easiest way to light a realistic scene either, just a way that forces me to undertand what i am doing.

[Blooz]

heres another exercise. i did a quick model of some image i saw and tried to light the scene. I kniow there is a funky glow on one of the chairs, in the bounce layer, i think that has to do with how i set the scene up, and im too sleepy to fix it right now.

key:
http://img231.echo.cx/img231/8774/key7lv.jpg

fill: it is blue because i noticed that there was some ;light out of the photo effecting the scene
http://img93.echo.cx/img93/3261/ambient1hb.jpg

bounce:
http://img93.echo.cx/img93/3189/bounce3vs.jpg

composite:
http://img93.echo.cx/img93/6319/composite4mf.jpg

here is another view of the scence, slightly different:
http://img93.echo.cx/img93/7919/test29uj.jpg

[greyface]

Hey, looking quite nice, there are two things you could improve:

1. The front side of the pilar is too dark, correct that in the bounce and key.
2. The left chair is too dark, should be corrected in bounce and key.

[jeremybirn]

The main issue I'd look at is the bounce lighting. Surfaces that are exposed to light bouncing around from any angle tend to get brighter than surfaces in cracks or corners. When you're doing bounce lighting, try to start with soft spotlights aimed just at the center of surfaces, and dropping off by the corners. The square column, for example, should get bounce light on all 3 visible sides, but it shouldn't be so flat and uniform, instead it should be brigher in the center, and darker where it meets the floor and walls. Also, the bounce on the ceiling needs to get darker around the edges of where the column or walls meet the ceiling.

If you have trouble doing all of this with carefully aimed spotlights, you can also darken areas with a negative intensity volume light just emitting ambience, not diffuse or specular. That could be perfect for the top of the column.

Be very careful when you render lights in layers about any shaders that use ambience or incandescence - you don't want them to appear in every layer, or they will appear too bright in the final comp.

-jeremy

[Aneks]

I think Jerermy is giving some awesome advice re using negative lights in areas which would have 'darekening' like the intersectio of column and roof etc. I also highly recommend looking at lighting in layers with a view to recombine them in compositing.

Looking at the style of render that you are going I am assuming that the lighting is fairly static ?

If so, another thing you might try is doing another 'grunge lighting' pass which emulates a dirtmap style ambient occlusion effect without relying on mental ray's calcualtion. Basically just paint some dirt/grunge textures for the corners of the room, points of geometry contact, nooks etc and render this to be used as a subtractive/multiply pass in comp. I used to do this alot before mr became available for maya.

Another thing might be to vary ammount of light diffusion and light reflection in your shaders. So that everything is not so smooth and CGI. I generally like to think of texturing/shader building and lighting as inter connected.

Your shaders and lights in concert will give you the pixels in you render and not either induvidually. The way light plays on a surface is largely effected by the nature of the surface itself, rather than just treating lights as buckets of illumination which you are throwing into the scene.

keep up the good work.

[floze]

I guess the most critical part is the balance of intensity and decay (falloff with distance). You never should use lights without decay unless you really need to. Check out my humble practice-gallery, all has been lit with linearly decaying lights:

http://individual.floze.de/index.php?id=49
http://individual.floze.de/index.php?id=46
http://individual.floze.de/index.php?id=51

It's far away from perfect as you can see, but you'll get the idea. The trick is to let one light 'fade' into the other. For example, in maya you can guess the distance where the light intensity of a linearly decaying light will be exact 1.0 by taking the intensity as a measure of distance - this way you get distance in centimeters. So let's say you have a light with linear decay and intensity set to 135, the spot where the actual 'shaded' intensity is 1.0 will be 135 centimeters away from the lightsource. That's at least how it works in maya, but the math behind probably applies to any other software.

It's the same story with quadratic decay, you only have to get either the squareroot of distance or square of intensity, depending what you're calculating - the example lightsource's intensity would be 1.0 at distance squareroot of 135 = 11.619 centimeters with quadratic decay.

But that's of course just the math. Just a guideline. With this kept in mind, you'll have (at least the feeling of) better control over what's actually happening.

[Blooz]

thanks guys i really do appreciate the feedback and especially the tips. I was wondering what type of lights you guys use when you have to do this type of rendering. I find that i only use spots, volume and sometimes an area light. My hardest problem (other than figuring out where to add bounce light) is working with the ambient pass. I still havent found a way to create accurate soft shadows for objects in the room.

floze: i went to your gallery and i must say awesome work. I was wondering how you are using point lights in your non-GI renderings, and how are you creating those nice soft shadows? i too use maya.

jeremy: thanks for the tip, i was wondering what basic rules you use when creating bounce light for and scene. I am still having a hard time trying to develope a consistant worklflow when trying to do the bounce lights (and the ambient lights for that matter)

[Osaires]

Hi floze nice renders

did you use the occlution inn the ambient channel or the diffuse channel?

would be nice to have a look at your light setup, mind to share screen shots,
or maby your sceen file, that would be greate;)

[floze]

Hi floze nice renders

did you use the occlution inn the ambient channel or the diffuse channel?
I used it in the brain channel! Heh, just kidding. Seriously, now that you say it, I noticed that I mixed up the images. It doesnt matter much anyway, have a look:

Without ambient occlusion:
http://individual.floze.de/fileadmin/Image_Archive/building_int_trad3_noAO.jpg

With ambient occlusion (sperarate pass, multiplied with a very low value over the original image):
http://individual.floze.de/fileadmin/Image_Archive/building_int_trad3.jpg

edit: I'd love to post shots of the lighting setup, I just cannot access my files since they are in Europe right now, and me is in California.. :argh:

[Blooz]

ok here is my next exercise, i picked a random image i saw on the internet and did a quick model of it, i also decided to try out the built in maya ambient occlusion shader.
http://img323.imageshack.us/img323/4205/room28au.jpg

it is a bit washed out in terms of contrast, this is because i am trying a technique i saw at cgarchitect which uses an ambient emiting volume light, i find that it gives decent control of ambience and contrast can be added by aiming negative shadow only spotlights.

here is the scene with occlusion:
http://img341.imageshack.us/img341/372/room2final6nh.jpg

i did notice that i am not getting correct shadows and occlusion with the glass table,i s there a way to remedy this, and what are your thoughts on ways this scene can be improved. I am also curious as to if there is a way to render a scene with occlusion without doing it in passes, this was done in two passes and composited in photoshop, i am aware that it is more flexible to do it this way but im just curious.

[jeremybirn]

Looks good! As you mention, removing the glass table from the occlusion could make it look better.

-jeremy

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