View Full Version : matte and shadow objects

11-24-2006, 02:02 PM
Hello Everyone
can someone help me to understand how I apply a matte shader to my objects
I just can't to figure it out or where the shader is locate

I just want to make a simple scene with a sphere and a floor and one light
I want the sphere to cast a shadow on the floor . but I dont want te floor to be seen.

Thanks in advanged for all the help

11-24-2006, 02:11 PM
In Surface Editor, under the Advanced tab, for Alpha Channel, try Shadow Density. On render, you'll get your matte in the alpha channel. I think this is what you're looking for.

11-24-2006, 02:44 PM
Thx Sekhar

I tried it out but it didn't work . maybe I need to active something else
so it will work ?

basically if my backdrop is white and I want my floor not to be seen in the
render , but I want it to get the shadow that the sphere cast .
it will make the effect of infinte floor or kind of a studio shot .
that's what I want .

11-24-2006, 04:05 PM
Well, you just get the alpha channel for matting out the floor, not the final image. On the Image Viewer (that has the rendered image), choose Alpha instead of Image on the top right. You'll see the matte covering the object(s) casting the shadow and the shadow itself.

To use this matte, save the render as Photoshop 32 and use the alpha channel to matte out the rest of the floor that you don't want. Then composite this on the background (in this case just a white layer) in Photoshop. If this is an animation, you could use a compositing software like AE.

If you want a more direct approach, check out the "Front Projection" option under Texture in Surface Editor...though in this case since your background is simply white, you could just match the floor color and get a similar result.

11-24-2006, 04:28 PM
Here's a simple example, if you need it.

11-24-2006, 07:04 PM
Thx For all the help Sekhar :bowdown:

The second method did the trick for me . but this only works if I got
a one color background
so I'll need to learn the first method too

the problem is that I don't know how to make a layer to mask another layer
in photoshop
if you could give me a brief explantion on how to do it I would be so happy
I'll also try to check for tutorial on that on the net

and again thanks for all the help and sorry for all the truble .

11-24-2006, 07:33 PM
No problem pawn, glad to be of help - that's why we're here.

Here's how you can apply the alpha:
(1) Open the image in Photoshop
(2) Go to the "Channels" tab and Ctrl+Click on the alpha channel (bottom)
(3) Go back to the "Layers" tab and click on mask icon at the bottom (third from left)

You now have the matte applied. You can then add the background as a layer below this matted layer.

11-25-2006, 02:09 AM
Thanks Thanks Thanks and again Thanks for all the help Sekhar
it worked like a charm .

11-25-2006, 10:12 AM
Glad it worked out, pawn.

Those interested in the sample, please use the below instead - in the earlier one above, I forgot to save the LWO with Shadow Density set for the floor.

11-29-2007, 10:04 AM
hey,i got the very same problem,except that my shadows are not completely opaque,and that's to be put over an image,and not a white background.so how can i extract only the shadows,and not just the alpha,as when grey,the alpha will let appear some of the texture under my shadows ?
like in max for instance on a matte shadow material, the material itself is transparent but the shadows appear.

11-30-2007, 03:29 AM
and to add that it doesn't seem to work with the shadows created with radiosity,the blurred shadow become sharp edged...