rendering shadow without ground plane for PNG file



I would like to get some help for rendering problem I have.  I am told to get PNG image for 3D model I made by Rhino.  And they don't need any background, but they need shadow of objects. How I can render shadows for objects without ground plane.


I try to use matte material behind the object, but there is still material left in the image PNG.

I appreciate if someone give me some advise.

Thank you.



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 What I would do is to use a plane object (not infinite) and make sure it's big enough to capture all of the shadows.  Use Matte material if you want to capture the background behind it.  Render that image.

Now open the "Render Pass Control" and turn it on.  Change the material replacement to "Luma Shadow Mask" and change the background to "Black".  Now render again.

Now you have a shadow mask to add into your image alpha channel.  Use photoshop to combine the masks and you're done.

 - Andy

Hi Andy,

Thank you for reply.


I appreciate your help for my question.



I tried to do the way you told me, but I think I got something wrong.

First image,I placed a ground plane below objects. I use Brazil matte material for a ground plane.

Second, I change Render Pass Control,  then it got all black.

I still have a ground plane to be shown in PNG.  I would like remove it, when I preserve the data as PNG.

Did I misunderstand something for what you told me?

Nope - the reason is that there are no shadows in the rendering.  When you said you wanted to capture the shadows, did you mean the reflections?

Yes,  I mean, I need object and the object's reflection with no background for PNG.

So sorry to make you confused.  Please tell me the way, if you know.  Thank you.

You can't do it in a single pass - so what I would do here is to first render as usual, and then do the following:

1) Create a new black environment

2) Create a "Brightness" material, with the amount set to 1.0 and apply it to all of the objects (not the ground plane)

3) Render.

You will get an image that has white where the objects and reflections are, and black everywhere else.  Use photoshop to set this image as your PNG alpha channel.

 - Andy

Hi Andy,

Thank you for reply, I appreciate your help.

I would like to know that, a new black environment means to create a new "basic environment"?

And, What kind of materials you would use for te ground plane or basement objects, which can get reflection from objects?




Yes - a basic environment with the color set to black would be fine.  And you can use a Brazil Chrome Material for your reflective objects.

 - Andy

Thank you!!  I will try the way you told me!!

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