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View Full Version : Can Area Lights impart "grit" at low levels?



Johnny
12-22-2005, 12:24 PM
I'm working on a scene lit by 1 area lights and a handful of spots. the scene is supposed to be a dimly-lit room, and I have the lights working the way I want, except that the scene seems to have a sort of grit over everything, similar to bad TV reception.

I am not using any kind of a plug to do this, but I wonder if it's a by-product of trying to produce a low-light scene.

any thoughts?

thank you!

J

Johnny
12-22-2005, 02:07 PM
no, in fact it's smaller..so that it can fit into a light fixture.

quality is at 5

thanks!

J

Johnny
12-22-2005, 02:14 PM
no, and I'm not sure that light(s) even are the cause... been trying to track down the culprit, changing settings here and there, but I don't see the cause.

J

Captain Obvious
12-22-2005, 04:02 PM
Turn off all lights, turn up your ambient, see if there still is noise.

Johnny
12-22-2005, 04:37 PM
OK..sorry took awhile, but here is the screen grab. two slices of the same map I'm using in that scene, but this "grit" is over the entire image.

the left part shows how it's rendered in the scene (as a painting on a wall), the right part is the actual map itself as seen in Photoshop. The white areas are supposed to be white with nothing in them except where they fuzz out at the edges. Granted, the rendered image is darker, but there shouldn't be any grit there.

thanks!

J
http://www.bluemitten.com/grit.jpg

Captain Obvious
12-22-2005, 05:03 PM
Looks like area light noise. You'll have to turn up your settings, I suppose.

Johnny
12-22-2005, 05:35 PM
Looks like area light noise. You'll have to turn up your settings, I suppose.


Hmm...it's at 5 now..guess I'm stuck.

Here's what it looks like with no lights, but Ambient turned up. darker, but grit-free.

http://www.bluemitten.com/nogrit.jpg

toby
12-22-2005, 06:01 PM
If you're getting area light noise at the max quality setting it means that either the light is very large, or the shadow that it's casting is very spread out.

Your options are to use shading noise reduction which can be kinda ugly, replacing each area light with 4 smaller ones, more anti-aliasing, or replacing the area lights with other types.

Lightwolf
12-22-2005, 06:08 PM
You could also render with motion blue, which will smooth down the noise of the light as well...

Cheers,
Mike

Johnny
12-22-2005, 06:28 PM
If you're getting area light noise at the max quality setting it means that either the light is very large, or the shadow that it's casting is very spread out.

Your options are to use shading noise reduction which can be kinda ugly, replacing each area light with 4 smaller ones, more anti-aliasing, or replacing the area lights with other types.

OK..on the notion of the spread-out shadow, that's a function of distance, IE, further away, shadow has a chance to spread out more.

My area light is small (like 0.015) so that it will fit into the "can" of a cieling light.

J

Bog
12-22-2005, 06:56 PM
That's a really small light.

What's the range from light-can to the target? Are your spotlights shadow-mapped? Is there really a God? Or is there some doubt? Well tonight we're going to sort it all out.... 'cause tonight it's the Meaning of Life!

My first two questions are serious. The other ones are because I finished work for the year.

I apologise for my exuberance.

Johnny
12-22-2005, 07:02 PM
heh..cool...I hope a few tall glasses of stout are being quaffed in celebration.

OK..spots in the scene seem not to be causing a problem..their shadows are ray traced.

on a hunch, I boosted the size of the area light and seemed to quash the "grit"

the range from the light can to the target? as in distance? about 2 meters give or take a little.

I might be onto something (correct me if I'm wrong) but the area light can't be too big OR too small. I thought I'd go from where it is now, and make it smaller and smaller until I get grit, then go back to a bigger size. I might have to use shields to still keep its role in the scene looking like a track light and not a huge wide light.

J





That's a really small light.

What's the range from light-can to the target? Are your spotlights shadow-mapped? Is there really a God? Or is there some doubt? Well tonight we're going to sort it all out.... 'cause tonight it's the Meaning of Life!

My first two questions are serious. The other ones are because I finished work for the year.

I apologise for my exuberance.

Johnny
12-22-2005, 07:35 PM
I might have been premature about getting rid of the grit here...still tangling with it and will post when something makes sense.

J

Johnny
12-22-2005, 09:58 PM
OK..after reading a thread on area lights elsewhere, I decided to

1. make my area light larger (closer to 1 than .015)
2. model a box around the light unseen to the Camera, but seen by light.

Things are a little better, but I'm taking a render hit.

Area lights are pretty nice..guess it makes sense they have a downside, too!

J