How to only render foreground objects to use PS for a background

[stelees]

Hi there,
I don't use vray much other than for rendering my fluid sims. I did a render of a wine glass with some wine poured into it and now a friend of mine wants me to do it bigger for her to put in the kitchen but she wants a grunge texture background.

What I want to do is just render the wine liquid and the glass with no background so I can put that into Photoshop and layer it over a texture she has supplied me.

I am not really clear on what render elements I should use to be able to not have a background to achieve this end result.

Thanks for any suggestions, I am sure this is obvious but can't put the pieces together looking in the doco (sorry old man brain at work here!)

S.

[fixeighted]

Simplest thing would be to add a background layer in the VFB, set it to 'save in image' and do it that way...no need to comp layers back.
Especially if you know the background size, just set the render dimensions to be equal to that.
Otherwise, if you need to play more with stuff then a back to beauty element can set all the layers for you.

[stelees]

fixeighted thanks for that. I have done that but I can't see the background. I am looking at the doco, I have added a background layer, found the image that was supplied, added it, ticked save in image but I can actually see it.
The render has nothing in the back ground. I have the glass, the fluid and lights. I know I am missing something here, just not sure what.

[stelees]

oh and also, will the background be visible in through the glass where the liquid is being poured?

[francomanko]

i might have misunderstood but cant you just render out the wine glass on its own then use the alpha in ps?

Failing that, use the vrayobject properties on the background geo, with matte object and alpha contribution of -1, affect alpha options....that way you keep the reflections/refractions from the backgorund in the glass

[fixeighted]

Here is a scene you can use to see what is going on https://www.dropbox.com/s/1ikj4ot447h3b5x/WINE.max?dl=0