Masking Problem

dhavalmistry · January 23, 2008, 05:51:23 PM

I am trying to mask out some clouds around the sun and I am getting weird results for some reason..

bigben · January 24, 2008, 06:12:34 AM

2 questions... how are you masking the clouds... and is the cloud's coverage > 0 ?

dhavalmistry · January 24, 2008, 09:42:00 AM

no I am using an image map as the blending shader of density fractal.

and yes the cloud's coverage is -0.6 in cloud layer

moodflow · January 24, 2008, 12:31:37 PM

Dhaval,

Not sure if you've tested this, but the image mask may not be 100% black in that area, so the sun is lighting it up. You may want to test that mask in Photoshop and see what value the color is in that area.

Nice test by the way.

dhavalmistry · January 24, 2008, 12:33:10 PM

the mask was made in photoshop with black brush with 100% opacity and 100% flow...

rcallicotte · January 24, 2008, 12:49:18 PM

Interesting. It's showing up around the square edges.

[edit - oh

I see now]

Oshyan · January 24, 2008, 05:11:01 PM

I see the same shape in your mask. I think it's a mask issue. However you should also keep in mind that using coverage adjustment in the Cloud Shader (as opposed to its density shader input) can cause odd results when using masks, etc.

- Oshyan

JimB · January 24, 2008, 07:14:18 PM

I can't even see what the issue is?

What specifically are you worried about? Be very specific. Is it the very dark blobs in the clouds?

moodflow · January 25, 2008, 03:24:16 PM

After looking at this more, are you using the camera projection method for the mask?

bigben · January 25, 2008, 04:05:36 PM

Quote from: Oshyan on January 24, 2008, 05:11:01 PM
I see the same shape in your mask. I think it's a mask issue. However you should also keep in mind that using coverage adjustment in the Cloud Shader (as opposed to its density shader input) can cause odd results when using masks, etc.

- Oshyan

I'll second that, hence my question. I'd try moving the coverage setting to the cloud's fractal first although in this case I don't think it will make a difference.

If you're using a through camera projection for the mask you have to remember that you are then boring a hole through the entire cloud layer. Even if the areas adjacent to the mask have only a minute amount of cloud in them this will impact on lighting by the time you take into account the cumulative effect through the entire cloud layer. This will lead to differences in shadows and atmospheric glow between the masked and unmasked areas which I'm guessing is part of your problem here.