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View Full Version : Easy scene, shadow gets messy.


LosPescados
08-05-2009, 05:29 PM
Hi, I first posted this in the 3DsMax section but I didn't really get an answer there, and I'm willing to proceed on this project:

I'm trying to do some light studies so I thought I make an Eastern alley where a wood construction's shade should be on the floor.

I tried using all types of light, and playing with their settings, but it always get messed up somehow.

Anyone can give some advice on which lights to use for this scene ? (better explanation at the picture below)
Also I'm a bit confused by the sunlight light, in real life, sunlight is mostly the only light source, how come people use specific lights for lightning there scenes?


the camera:
http://i32.tinypic.com/98zifr.jpg

the scene:
http://i32.tinypic.com/152c0oz.jpg

Trauco
08-05-2009, 07:44 PM
You should mention what is the renderer you are using if you want a more specific answer, but i'll give it a go.

The problem with your scene is that it is only iluminated with a skylight, a kind of light that does not try to resemble sunlight in any way, it just tries to simulate the effect of diffuse ambient light (that is light that has bounced many many times over a lot of surfaces).

What you need to simulate the sun, is to use a "direct light" without any kind of fallof or decay aimed at your scene at the angle you want it to be (a 3ds max light type that shoots parallel rays).

The other way (and the realistic way) is to use a "Daylight" system (you can find it under the "systems" tab), that one is a little harder to configure the first few times.

and why people use all sorts of lights to iluminate scenes... well, it is because of the effect they want to achieve, and if you know how to configure them you are not counting on luck to achieve good results. Keep in mind that most light rigs simulate real rigs used by photographers, moviemakers, etc.

LosPescados
08-05-2009, 07:58 PM
I'm trying to get what you say as I'm totally new to lightening.
I'm using 3DsMax9 (if that is what you are asking).
I tried to achieve it with a direct light, but I did get a circular range of light. And If I putted the light further away, the shade gave a really ugly shade, (you couldn't see
the cylinders shape anymore)

EDIT: nvm, found the option 'rectangular'. I must have overlooked it when I was looking through them.

Thank you for your help!

EDIT2: current scene,
The part at the green box is still quite dark.. Any ideas on how to solve this ? I simply used a direct light which is in top of the camera.

http://i26.tinypic.com/rrp62q.jpg

Trauco
08-12-2009, 10:55 PM
You could use a omni light close to that building's wall, to fake the rebound light from the ground into the wall, and then into the green block.


That light has to have a small falloff.

Or you could add a skylight to your scene and get the soft shadows and subtle illumination.

Or you set a omni light as "ambient only" again with a small fallof, and place it near the place where you want to reduce contrast.

PS: By the way, i've noticed that you are using "shadow mapped" shadows, you could increase it's "size" in the shadow map paramenters of the direct light. (something around 1024 would be fine), that way you wont get jagged edges in the shadows from the direct light.

sundialsvc4
08-13-2009, 02:42 AM
Another "point to ponder" is this:

Sometimes, when you're thinking about "lighting," you're actually concerned with shadows. In the magical world of computer graphics there is actually such a thing as "a light that only casts shadows."

When you are concerned with "adding light," you should also bear in mind that you can easily do things with CG "lights" that are not possible in the real-world. Aside from the fact that you can't "see" a CG light even when you are staring directly at it, you can arrange for a light to only illuminate certain objects in the scene and not others. You can also very directly control just how the light contributes to the scene.

Finally, "compositing is the way to go." You can compose a scene of many "layers" of objects each with its own illumination. Having rendered them once, you can exercise all sorts of color-grading, contrast control and other things with respect to the imagery you have produced.

For example, in this case: "tell all of the lights not to cast any shadows at all. (In the magic world of CG, they can do that.) Then, produce a layer using shadow-spotlights which contains shadows ... and absolutely nothing else. (Look at the tape and you'll see a blank blue field with nothing but shadows, as they would be cast upon the invisible objects.) Now, in your compositing program you can "dial-in" as much or as little shadow as you need: color, intensity, alpha. It is literally just like the "mix-down" process that is used with multitrack audio recording.

You might say, "gee, that's a lot of extra work!" Well, it is and it isn't. Producing the various layers of material takes time (although usually your render-pipeline can generate many different component outputs at once), but, having produced a particular thing once, you don't have to re-produce it. You're pushing knobs up and down in real time and seeing real-time results. You're not saying, "whups, I gotta go re-render this ... see ya in a couple weeks..."

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