How to separate shadows from rest of render?

[helpdesk]

O.k. I am a newbie when it comes to separating out passes in VRAY.
I have an image I need to get the shadows separated out so that I can compose it in Pshop on a different background terrain. How can I do this?
I have read info on Gbuffer and it doesn't sound like a viable option since I don't have after effects here. I do have Cebas PSDManager, but I can't get it to work properly with VRAY for some reason. Any tips or help would be greatly appreciated!
Regards,
Dave Vaughn

[Candelero]

You have to USE the G-Buffer,

#1 in the G-Buffer/ColorMapping rollout - select the Shadows ;
#2 Use the V-Ray VFB ;
#3 Check ON << Save separte G-Buffer channels >>

Best Regards,
nikki Candelero

[helpdesk]

O.k. Then what foramt do I save it out in then? I thought that the only way to use GBuffer was RLA or RPF?
How is this useful in photoshop?
Should I use a VRAYMatte for the ground plane to capture the shadows?

[Candelero]

O.k. Then what foramt do I save it out in then? I thought that the only way to use GBuffer was RLA or RPF?
How is this useful in photoshop?
Should I use a VRAYMatte for the ground plane to capture the shadows?

It all depends on what You need as a final result...
As for the format - should be good to use one which supports the Alpha channel, in case You need to Separate it...

If You just need the Shadows... without the underlying object...
Matte should be necessary as well...

Best Regards,
nikki Candelero

[helpdesk]

This is what I am trying to do. The Bldgs and roads...I want to have rendered in VRAY with Accurate shadows so that I can put this on top of my Landscape image...I tried to assign a white shader for a ground plane in VIZ and this is clearly not the way to do it. So, Should I assign a plain old default gray VRAYMAT to the ground plane and change the VRAY properties for that plane to Matte object right? What else needs to be toggled on to get this to work in the Matte properties? I have GI and A VRAY sun going on so Direct light should be turned on also then right?

Can't I upload a small jpg to show what I am doing? I don't have a URL I can post it to right now.

[TRGraphics]

Does the new build of vray allow saving g-buffer data now if you use DR?

Can you be more specific on saving a seperate shadow pass.

Say there is a ball sitting on a plane with one spot light, environment light set to 1 and GI. Exactly what needs to be checked under g-buffer inorder to be able to adjust only the shadow intensity in Photoshop.

Sorry for the stupid question but I can't get it to work right either.


Tony

[vlado]

Does the new build of vray allow saving g-buffer data now if you use DR?

Yes, it does generate render elements in DR mode.

Say there is a ball sitting on a plane with one spot light, environment light set to 1 and GI. Exactly what needs to be checked under g-buffer inorder to be able to adjust only the shadow intensity in Photoshop.

You need the scene color channel, the diffuse channel, and the shadow channel. Multiply the shadow channel by the diffuse and add it to the scene. This will remove all the shadows. By adjusting the degree to which the shadow x diffuse is added to the scene, you can control the shadow strength.

An quick example:

Here is the full scene color channel:


Here is the diffuse channel:


Here is the shadows channel:


Now, if we take the shadows and multiply them by the diffuse in PhotoPaint, this is what we get:

Here is how they are combined:


These are exactly the missing shadows in our color channel. If we take this result, and add it directly to the color channel, this is what we get:

which is exactly the scene without any shadows.

If we don't add all of the multiplied shadows, but just 50% of that, here is what we get:

which reduces the shadows in half compared to the original rendering. Here is the combination this time:


I used PhotoPaint for this since I don't have experience with PhotoShop, but I imagine it will translate more or less directly.

Best regards,
Vlado

[TRGraphics]

Thanks vlado, that makes it very clear. And good news about DR and g-buffer!

I have a client who wants to be able to adjust only the shadow intensity for a furniture color brochure. Very picky little fellow. Thanks again.

Tony

[DaForce]

Thats handy to know Vlado, infact perfect timing... just what i needed.

Thanks

[rpc212]

Thanks Vlado! Been wondering how to do this!

Cheers!

[SteveC]

cheers vlado, also been wondering how to use the gbuffer and render out layers.

Photoshop users probably already know this, you need to flatten the image with the diffuse and shadow channels in, then import in to the colour channel image. Once in the colour channel image, use colour dodge on your shadow layer and control the intensity of the shadows with the opacity spinner.

Thought i'd post this cos i got a bit lost after importing the shadows in to the colour image

stevec

[TRGraphics]

This works well for regular vray materials but I can't seem to get it to work with a matte material on the floor. It won't ouput a shadow channel using a matte material.

[vlado]

This works well for regular vray materials but I can't seem to get it to work with a matte material on the floor. It won't ouput a shadow channel using a matte material.

Yes, this won't work at present since the matte material already allows you to have the shadows in the alpha channel.

Best regards,
Vlado

[DaForce]

haha was just going to post saying the same thing!!

Vlado,
Can you poke your head in over at this thread.
http://www.chaosgroup.com/forum/phpB...asc&highlight=