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Message 1 of 11
Anonymous
589 Views, 10 Replies

Shadows

Ok I have aked some stupid questions lately and this may be another..
When I render my shadow pass and go over to the FX tree to try and composite , why are they white? instead of being dark like they are in the shot?

I know when you see the pass they look white which I think is normal or, the white parts are the shadow I get that. Its when I composite should they not be dark like shadows?

G
10 REPLIES 10
Message 2 of 11
Anonymous
in reply to: Anonymous

I'm not certain, but I would guess that it basically renders out the shadows as a mask, which then gets used to isolate certain operations (such as color corrections) during compositing, giving you more control over the appearance of the final shadow.
Message 3 of 11
Anonymous
in reply to: Anonymous

The Shadow Passesfrom the Help XSI
The Shadow Passes
Rendering a shadow on its own and being able to composite it back in the final render allows you to edit a shadow’s blur, intensity, and color without having to re-render the entire scene. This can be a great asset when production time is limited. Shadow presets create an alpha matte of the shadows cast by objects in a scene.
Two shadow passes are available by default: the shadow pass and the selective shadow pass.


looks like works like a cookie cut.

i don't know how you set it up in a composting program. i assume that might be something like occlusion that you set the pass as multiply.
Message 4 of 11
Anonymous
in reply to: Anonymous

I've still not worked it out.. Been working on other parts for now. But I did once have the the way I wanted. It seems like the shadows need to be inverted?

I have no idea..
G
Message 5 of 11
Anonymous
in reply to: Anonymous

blog.pigeonimpossible.com/?cat=9

1 of his pod cast he mention how he did it with shadow, just the pass, dosnt say to much on how he use it for the composition.
Message 6 of 11
Anonymous
in reply to: Anonymous

It might be just what I am after..
Message 7 of 11
Anonymous
in reply to: Anonymous

Removed due to a previous post being edited
Message 8 of 11
Anonymous
in reply to: Anonymous

well after you do your shadow pass,
how you apply it to the composition?
Message 9 of 11
Anonymous
in reply to: Anonymous

bring your shadow pass (white shadows, everything else black or grasyscale) into the compositor

invert shadow pass
get a math composite node (if using FX tree)
plug your color pass into the bg input of the math comp
plug shadow pass into foreground of math comp
set math composite to multiply
(Black * foreground color = black )
(White * foreground color = foreground color)

You can blur your shadows using a blur filter (gauss)
however if you notice the shadows tend to shrink a little and create a light gap between the shadow line and the contact point on the object casting the shadow..
you can get away with it at a distance for medium to far distant objects,
but for closeups this blur trick will fall apart.

You can solve this by using the same preset shadow pass, and adding another entry to the shadow object partition override

Add in the primary rays attribute for all objects in the partition and disable them in the override. This way you will get the entire shadow being rendered, even the portion of the shadow that sits underneath the character.

From there, you can blur away as much as you want without ever losing the contact shadows.

You will likely also need to render a matte pass to comp the shadows properly for some of your closeup objects, otherwise the portion of the shadow rendered where the character had previously blocked it (primary rays on) will multiply overtop and darken the character incorrectly.

Hope this helps some.

The other option is to just turn on area lights and render soft shadows directly in your shadow pass to bypass the whole primary ray , matte pass steps.

Adam
Message 10 of 11
Anonymous
in reply to: Anonymous

that is very instructive, thanks
i will give it a try as soon we get some render to play with them =).

Thanks again.
Message 11 of 11
Anonymous
in reply to: Anonymous

Or...

Just uncheck RGB from the shadow shader. You really only want the shadows to affect the alpha channel with a black render. That way it comps in properly as is.

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