Shadow Catcher alpha problem

[pixelsim]

Hi

When rendering an image with shadow catcher on gpu the Alpha looks terrible. If I turn the Alpha type back to Opacity the alpha looks as expected.
This is when using gpu bucket or RT
The results are as expected with cpu render

I have attached the alpha (as jpeg, sorry) to show the difference when shadow catcher is on and off, as well as cpu working correctly. Also a screengrab from the frame buffer where there are lots of coloured pixels in the alpha too.


I just wanted to find out if I am doing something wrong when trying to render an image with shadow catcher on gpu. The result I want is a clean alpha with shadow so that I can add a background after rendering.
I was using a work scene which i cant show. But re created a scene with a couple of standard objects
File is attached as well
All I have done in the file is turn "shadow catcher" or "opacity" on in the alpha type in the shader, material named Shadow

thanks
Simon

[Muhammed_Hamed]

There is a better workflow for this with Multimatte,
See here,
https://www.youtube.com/watch?v=28Um3KogHR8
The Alpha issue is a GPU rendering limitation, that is not specific to Vray GPU

[pixelsim]

Hi Muhammed
Thanks for pointing me to a workaround.
I did search through the docs but couldn't find anything about Shadow catcher not working with GPU

thanks again