How can I remove objects from the Alpha Channel when rendering?

[yuriykurri1]

Hello!

 

I have a scene with a character and floor mesh objects, as well as a basic light setup. The floor has a white vraymtl, and the background is white as well from the vray dome light.

 

Question is, how can I make it so that the floor mesh shows up in the RGB Color channel for the shadows, but does not show up in the Alpha Channel?

 

I provided a screenshot as well...

 

Thank you.

[Francisco Penaloza]

If you are using VRay you have a few options.

One would be to do right click on the mesh and choose VRay properties, in there you can choose if that mesh will be skipped by the alpha channel, between many other options.

You can also use a VRay material wrapper, in there you can find similar options.

[yuriykurri1]

Using the wrapper mat worked but I noticed an issue. When I save out the render to a PNG, the shadows on the floor are no longer there.

 

I am also using Render Elements with a dirt texture to render out the ambient occlusion pass... should I just use that for the floor shadows?

 

Still curious why I dont see a shadow on the saved PNG file, but I do in the Vray render window.

Edited October 10, 2019 by yuriykurri1

[yuriykurri1]

Using the Vray mtl wrapper worked... sort of.

 

It doesnt show up in the alpha channel anymore but when I save the render as a PNG, the shadows on the floor are no longer there.

 

When I save as a JPG, they are there.

 

I guess this has something to do with the Alpha channel on PNG files... is this normal? Shouldn't the shadows still be visible on the PNG file?

[Tom Bussey]

The shadows need to be cast on to something. As you've noticed they're not there because the object they're being cast on to is clipped out by the alpha. You can capture an alpha of the shadow, I can never remember the exact settings, but look in to matte objects and 'shadow catcher' planes. I think the vray toolbar has a one button solution for this, but better to understand it. Essentially your ground plane is set as a matte object with no alpha contribution except for the shadows. It's all in the Vray Object properties dialogue on the right hand column.

[guenther Malek]

I guess your shadow is too weak to be seen in the alpha. Give it try with a light source that cast a strong shadow (daker environment) and show us your result.

I made the experience when composing the image later in Photoshop, that he shadow from the alpha is not as strong as in the rendering. In your case it´s really faint you can hardly see it in RGB...

 

I am also stuggling with Matte Shadows (as you can see in my next post)

Edited October 24, 2019 by guenthermalek