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mjkennedy
02-11-2009, 06:15 PM
Hi,

I'm trying to light an outdoor scene, and having some trouble.

Firstly, there's what lights to use. I know that you supposed to use a "main light", that acts as your Sun, and casts shadows.

However, it's how to "fill" the rest of the scene that's giving me trouble. I have the ambient turned all the way down. So any surface that is not being hit directly by the main light is black. I turned down the ambient light because a) I find it makes things look washed out, and b) I was taught it should always be turned off. Am I right in doing this?

So, to get rid of the black areas, I have to use 2 or 3 more infinite lights. This seems sloppy to me (maybe it's how you're supposed to do it... but it doesn't feel "right" to me).


I also played with FG. I could maybe use this instead of all those lights? But I'm having a few problems with that too:

1. FG just renders a black scene unless I have at least one infinite light turned on. I was under the impression that FG and GI didn't need the help of any prexisting lights to light a scene. Am I just doing something wrong here, or does FG need to be used in conjunction with traditional lighting? (I would think yes, especially for the "hard shadows" of the sun)

2. I have a sphere with a blue sky texture applied to it which encompasses the whole scene. When I turn on FG with one infinite light, the whole scene turns a bluish hue (presumably because of the sky). Obviously I don't want this, as I'm trying to create a mid-day sun sort of look. Do I need to omitt the sky from the FG in order to ditch the blue?

Overall, I'm just frustrated that what seems like it should be fairly easy (create a scene that looks like the outdoors, lit only by the sun), is proving so tricky.

Any suggestions on the best method to tackle outdoor scenes would be greatly appreciated.

Thanks so much,

Matt

PS As always, I've had a look through previous posts, but couldn't find anything that answered my questions.

mister3d
02-11-2009, 07:11 PM
Hi,

I'm trying to light an outdoor scene, and having some trouble.

Firstly, there's what lights to use. I know that you supposed to use a "main light", that acts as your Sun, and casts shadows.

Right.


However, it's how to "fill" the rest of the scene that's giving me trouble. I have the ambient turned all the way down. So any surface that is not being hit directly by the main light is black. I turned down the ambient light because a) I find it makes things look washed out, and b) I was taught it should always be turned off. Am I right in doing this?

Right, because it doesn't give you any shading. It doesn't take into account any light, and just brightens the shadows, so to speak. it is very unrealistic. A correct solution is global illumination, which simulates the way light reflects in real life: the first ray goes from the light source, hits the surface (you have black shadows, because light didn't go any further than one ray, no bounce yet). Global illumination continues light travelling, taking into account the surfaces the light ray hits going further.


So, to get rid of the black areas, I have to use 2 or 3 more infinite lights. This seems sloppy to me (maybe it's how you're supposed to do it... but it doesn't feel "right" to me).

The point is to make the shadows from the sky (your second source) very soft. They are soft because the area of the sky is very big. In most packages you have a skydome, or a skylight source. An old way is to place a lot of lights in a hemisphere manner, which the skydome makes automatically. Basically it is a number of lights which emit rays in a hemisphere manner. Which package and a renderer do you use?


I also played with FG. I could maybe use this instead of all those lights? But I'm having a few problems with that too:

1. FG just renders a black scene unless I have at least one infinite light turned on. I was under the impression that FG and GI didn't need the help of any prexisting lights to light a scene. Am I just doing something wrong here, or does FG need to be used in conjunction with traditional lighting? (I would think yes, especially for the "hard shadows" of the sun)

It is not a lightsource, it's just one of techniologies used to simulare indirect, or global illumination. It just continues the light travelling after it hits the surface. See the second post in this thread, and the first teapot has not any indirect illumination. http://forums.cgsociety.org/showthread.php?f=21&t=650761

This is very simple: imagine a ray hitting a wall, or a laser. If it hits the wall and doesn't reflect, it is direct illlumination, which you have when you create any spotlight. Anything else will be black which doesn't fit into the area of direct affection.
If the ray reflects, you have indirect illumination, because light continues to travelling and bouncing. FG, and other technologies, like photons, light cache, monte-carlo, radiosity all do one simple thing - continue reflecting the light to get rid of black shadows. This is all global or indirect illumination, this is the name of the phenomenon that happens in real life. Don't confuse it with names of technologies which I listed, those are just local cases of simulating it.


2. I have a sphere with a blue sky texture applied to it which encompasses the whole scene. When I turn on FG with one infinite light, the whole scene turns a bluish hue (presumably because of the sky). Obviously I don't want this, as I'm trying to create a mid-day sun sort of look. Do I need to omitt the sky from the FG in order to ditch the blue?

Well it looks like a correct thing happening: if your sky is blue, you get blue tint of lighting. You better to match the color of light to the color of sky.


Overall, I'm just frustrated that what seems like it should be fairly easy (create a scene that looks like the outdoors, lit only by the sun), is proving so tricky.

It is indeed not too hard nowadays. Just find a lightsource that simulates the sky in your package. Place it, place the sun, adjust the colors based on the environment, and the turn on FG for indirect illumination.
FG cannot make any light as it is a technology of prolonging light reflection, not emitting any light.

FreshFX
02-12-2009, 09:25 AM
Funny you bring this up as i do also find it very hard to light exterior scenes. Whenever i do have to light a outdoor scene i normally start with 3 lights as the key and 1 fill light.

I also work in Maya so the new sun & Sky feature is just pro when it comes to easy sun / Sky light simulation!. But other than that in all honesty, im not really a lighting pro but as i said when i have to do it...It normally involves quite a bit of tweeking and small adjustments till you hit the right spot !..

I know this probably didnt help so much but its always good to hear how others do it no matter what they do / processes they use themselves :)

Good luck man !

mjkennedy
02-13-2009, 05:01 PM
The point is to make the shadows from the sky (your second source) very soft. They are soft because the area of the sky is very big. In most packages you have a skydome, or a skylight source. An old way is to place a lot of lights in a hemisphere manner, which the skydome makes automatically. Basically it is a number of lights which emit rays in a hemisphere manner. Which package and a renderer do you use?

I'm using XSI. I'm not sure XSI has any such feature. Any ideas or links to tutorials on how I could successfully build such a rig?



Well it looks like a correct thing happening: if your sky is blue, you get blue tint of lighting. You better to match the color of light to the color of sky.

The problem is, the blue is WAY too blue. There must be some way to tone this down?


Thanks for the help!

Matt

mister3d
02-13-2009, 05:19 PM
I'm using XSI. I'm not sure XSI has any such feature. Any ideas or links to tutorials on how I could successfully build such a rig?




The problem is, the blue is WAY too blue. There must be some way to tone this down?


Thanks for the help!

Matt

Google gave a lot of links on "xsi physical sky", so there should be one. http://www.google.com.ua/search?hl=uk&q=xsi+sky&btnG=%D0%9F%D0%BE%D1%88%D1%83%D0%BA&meta=

About the color of the sky, try to search for "color bleeding" control in help files. I guess it is in fg setings. it is present in most modern renderers (and old too).

mjkennedy
02-16-2009, 12:54 PM
Google gave a lot of links on "xsi physical sky", so there should be one. http://www.google.com.ua/search?hl=uk&q=xsi+sky&btnG=%D0%9F%D0%BE%D1%88%D1%83%D0%BA&meta=

About the color of the sky, try to search for "color bleeding" control in help files. I guess it is in fg setings. it is present in most modern renderers (and old too).

Hi,

I tried Physical Sky/Sun. Overall it looks pretty good, but I'm having one significant problem. The shadowed areas of the scene are too dark. I tried making them lighter using the "simple tone mapping" camera shader, but that washes out the scene big time. Doesn't look good.

Any idea how I could brighten the shadows in my scene (while using physical sun/sky and FG)?

Thanks again,

Matt

DanielWray
02-16-2009, 09:12 PM
Hey, i dont use any the mentioned software, so i dont have experience with it.

However when im ligthing in my softaware to light the shadows i choose a lighter colour i.e. medium to light grey, coupled with soft edges they look really good.

However for shadowing an outdoor shot i would use a light blue tint for the shadowing.. light color warm = shadow color cool.

Also seeing a screenshot of the scene would help us since you could scrap the Global illumation method all together and place very dim area lights and spot lamps in key locations where you want the high lights or indeed shadows, by setting the lamps to a minus emittence level.

Sorry if this post isnt extremley helpfull, but it's all i can really offer.

israelyang
02-17-2009, 10:45 PM
sounds like you are working with MR, then you might want to read Florian's tutorials, very simple setup and very beautiful results.
http://www.floze.org/2008/07/six-tuts-on-light-and-shade-part-i.html

In an ideal sunny exterior, (To make it easier let's say you are in Toronto and everything on the ground is covered by snow and white.) imagine you have 2 main light sources.

One is your sun, one is the sky. the sun is a hard light source.
The sun illuminates from infinite far thus we simulate it in 3d with a directional light. However if you choose to use depth map shadow you might find it easier to control the illumination area using a spot light.

Another light source is the sky. The sky is a soft light source.
In a sunny cloudless blue sky day, if all of a sudden a runaway cloud moves in and blocks the sun, the sky becomes the only illumination of the scene. Everything now is lit from all direction by the bright blue sky, you no longer cast a sharp shadow but a very soft one since the illumination is coming from all angles.
At this moment, if you pick up a (digital) camera and set its color balance to day light balanced and take a picture of your surrounding, you will find everything appears blue. You then ask yourself why your eyes see everything just light grey. Because your eyes/brain (I hope) actually perform a instant color balance to make the snow covered land it appear grey/neutral.

Now if we combine both light sources sun and sky, you should find objects in the shade to have the same soft shadowing you once observed while the sun was behind the cloud, and now all of a sudden the shadow part on the white snow appear a lot more blue, it's because the sunlight is now so much more intense, you eyes are now balanced the the sun light, so the shadow look blue since it's being illuminated by the blue sky.

That's why I wouldn't recommend changing the 'color of the shadow' in 3d as in 3d, it's only going to change the color of the shadow that's 'cast', while the 'unlit' side of an object remains black. The colour we observe in the shadows in real life come from the illumination of the sky.

The ambient light is still being used on projects that cannot afford GI.
To see how one may use it, read Master Zap's entry on
"The Joy of a little "Ambience"..."

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