Isolating a background

neospace · 27 Oct 2009, 06:01

hi, am new to Vray fro SU. Is it possible to isolate a background when renderimng in Vray so that the rest of the model renders and not the background. I have imported a 'sky and clouds' jpeg as a background in my SU model. but when i render, the white clouds and blue sky merge to give me a light blue gradient (and clouds disappear).I woudl like to keep the clouds and sky as is.
or are there any settings that i have to check?
thanx

thomthom · 27 Oct 2009, 07:26

You added the background in the enviroment section, right?
Go to the VFB section and add the Alpha layer. When you save the output it will create a alpha channel image as well.

neospace · 27 Oct 2009, 12:54

hi thanx for the reply.
please explain the second part - how do I add the alpha layer in the VBF section as there are only preset options and nothing to browse and choose the alpha layer.
thanx

holmes1977 · 28 Oct 2009, 06:18

Hi neospace

Go to V-Ray option
Go to the VFB tab
Select "Alpha" then press add

Once you have saved your rendered image, you will notice there are 2 images, one being the alpa map (background mask)
Hope I am not putting you wrong. Im still learning myself.

neospace · 28 Oct 2009, 07:00

hi thanx
when i choose the VFB Tab in Vray, i dont get an ' alpha' option in the drop down menu, only 'atmosphere, diffuse, shadow etc'..
what am I doing wrong?
thanx again

holmes1977 · 28 Oct 2009, 07:18

Hmmmmmm, have you scrolled down the list. They are not in alphabetical order which fooled me the first time I was looking for the alpha channel.

Appart from that, I really cant help you. You may have to wait for Thomthom to get back online.

thomthom · 28 Oct 2009, 07:26

Should be there on the list.
...all though, are you using the original version by any chance. I think it might not have been present with that. But then it automatically saved an alpha channel image along with your diffuse.

neospace · 28 Oct 2009, 07:47

its definitely not there,
or am i not aplying it correctly in environemnt tab

in environment, i scroll down choose bitmap
click M next to bitmap
-select my image and apply
create a seperate alpha image in my graphics application
correct so far right?
is there any other way to do it?
maybe my Vray needs an upgrade
thanx alot to both of you though

thomthom · 28 Oct 2009, 08:20

What version of VfSU do you have? Lets get that established first.

neospace · 28 Oct 2009, 10:36

okay Thom seems u were right, my Vray is older version
I've installed latest demo of Vray.
Found the 'alpha' option in drop down menu in VFB tab,checked it.
what do I do next?
(if i render as is, i get a black background)

thanx

thomthom · 28 Oct 2009, 11:13

You need to increase the multiplier of the background map. At least when you use physical camera. Between 20-40 I think.

btw, a note on the latest version:

Never apply materials to groups/components - it makes the parsing time of the model (before it starts rendering) insanely large. Plus, it makes smooth geometry render faceted.
When you modify materials, make sure you open the Option window before you save - otherwise all your material changes will be lost.

neospace · 28 Oct 2009, 15:55

Thanx Thomthom and Holmes for your help, appreciate it.
You actually dont need to play around with the alpha
-in Environment tab in BOTH the Sky and background tabs, choose bitmap and place your HDRI.
choose environment as opposed to Texture on the top

Put your physical camera off and render!
you'll probably need to adjust your blur and multiplier values, as your first rendering will most likely be too dark or too light and blurry.
Jorge Barrero's 'V-Ray for SketchUp Tutorial - Sun & Sky - Beginner' on Youtube explains it nicely.
thanx again
If ever you guys are in South Africa give a shout, my email: neospace.studio@gmail.com