Only shadows on matte in alpha

[Metin_7]

Hi,

I've got a matte plane in my scene that receives shadows from objects. I want only the shadows in my alpha, so I can easily change the background color.

I created a plane, gave it a VRay material and checked the object's alpha checkbox in the system settings, turned on shadows and affect alpha and turned the alpha spinner to 0.0.

I seem to remember that an alpha setting of 0.0 caused the alpha of a matte plane to only capture the shadows on it, but not the plane itself. But I get nothing at all (the same result as an alpha value of -1), while an alpha of 1.0 gives me a completely opaque alpha, which is not what I want either.

Can anyone please help me out? Thanks very much in advance!

Cheers,

Metin

[v_wrangler]

You don't want the shadow-casting object to appear?
If so, you can uncheck the object's "visible to camera" property

[v_wrangler]

NOw if you want the object to appear in the RGB channel but get matted
out in the Alpha, Make sure the obejct is visible to camera, set its
VRAY properties with alpha contribution to -1 (if you set it to zero, the
alpha will have only the shadows) , without checking the Matte Object
checkbox. That (Matte Object) checkbox is just a flag whether the object
will be visible or not in the RGB channels.

Also Make sure the Shadows, Affect Alpha checkboxes are on.

Not sure if this is what you are after (my english comprehension stinks! - sorry)

[Metin_7]

Thanks for your explanation Roy. I actually don't know either if you understand what I mean.

I'll try to explain it in a different way. With the standard Max matte material you can make a matte plane and put let's say a cube on it. Add a shadow casting light and your alpha will show an opaque cube and only the shadow it casts on the matte plane in the alpha channel, but not the plane itself. This is very useful if you want to change the background color or bitmap afterwards, but don't want to lose your shadows.

That's how I'd like a VRay matte plane to behave as well, if possible: purely as a shadow catcher. I seem to remember that a VRay alpha contribution value of 1 made an object completely opaque, 0 only showed the shadows (as I want it) and -1 was completely transparent. But as a VRay matte doesn't work like that right now I'm doubting if the shadow-catching is maybe only a feature of the standard Max matte material?

Thanks again and cheers,

Metin

[vlado]

In the object settings for your matte object, you need to turn on the matte option, set the alpha contribution to -1, turn on the shadow and affect shadow options.

Setting the alpha contribution to 0.0 means that the object will not show up the alpha channel - at all, shadows or no shadows.

If you want the shadow to be visible in the RGB channel as well, you will need to set the background to something different than black.

Best regards,
Vlado

[Metin_7]

That's great, thanks very much Vlado!

Cheers,

Metin

[v_wrangler]

Hahaha. Since Vlado already came to the rescue - I think I'll just shut up
now

[Viscacha]

here is a thread about the same thing, and i posted examples in case it helps anyone with the same problem.

http://www.chaoticdimension.com/foru...t=matte+shadow