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Hi,

I'm rendering two side tables that I later wish to insert into one specific background image. http://imgur.com/00KlvWT

First, I got confused wether the tables will cast a shadow or a reflection on this floor. I am thinking that because of the shiny floor, there will be a reflection and no shadow (?)

With this background idea, I am rendering the tables with suitable lighting, alpha channel and a ground plane that I hoped would catch the reflection from the tables. However, as I don't want the ground plane in my final render, I am setting this as "invisible to camera".

My problem is that the reflection does not get included in the render (or in the alpha channel). I just get the tables and nothing else.

Anyone here with a soloution to this issue?
Thanks a lot in advance.

//Karolina

This can be done.

Check this out..

http://forums.cgarchitect.com/71077-only-shadows.html

Haha. I answered that thread too.

do-do isn't asking about a shadow catching plane, he's asking about a reflection catching plane.

Here's what I did:
1) Place your subject on a plane. Give the plane a shadow catching material.
2) Render the floor, with subject hidden to camera:
Shadow


Render


3) Put both these images into a Photoshop document. Invert the shadow pass so you get this:


4) Use this inverted shadow pass as a mask for your rendered floor layer. This will give you something like this:


5) Put your photo on a layer beneath all this. Comp'd together it looks like:


6) Render the subject with floor hidden, and add on top of this comp:


Tweaking the brightness/contrast of the floor mask will result in stronger/weaker floor reflections. Changing the blending mode of the floor layer will allow you to tweak how it looks against the photo.

I get the point in both of your replies. 1 000 000 thanks for excellent explaination!