Vue Alpha Matte

#1

I’m getting bad alpha channels in Vue 7 xStream. Is there a way to generate a cleaner alpha matte?

I’ve search all over but haven’t found anything yet. Thanks in advance!

#2

im getting the same thing when I’m using alpha planes in ecosystems. Ive tried adjusting the alpha channels of the texture, adjusting the transparency function etc…searched the web, didnt find anything usefull:(

#3

Hi, is your alpha map a few pixels smaller than your color map? If your alpha map is the same size as your color map then you will get a few pixels of white around it. Another thing I do is to make the edge of my color map a little wider so that the color map isn’t going from a green tree to a bright background.

I don’t know if this is a flaw in Vue 7 as I only have Vue 6 Inf., but I thought you could give this a try to see if it helps. :slight_smile:

#4

I just came here for this same reason: I, as the original poster) cant get good masks in Vue. Anyone knows why?

thanks in advance

#5

Here’s how to get rid of all that nasty white fringing. It’s caused by two things - the anti-aliasing vue does to smooth out edges, and the fact that the alpha channel isn’t pre-multiplied.

If you are using a compositing package, the process is pretty straightforward:

  1. Render out a standard, full colour (rgb) image, an alpha mask, and a ‘multipass’ render containing the layer ‘background’ from vue. DON’T do any post-process exposure adjustment of any kind, and don’t compress the files.

  2. Subtract the ‘background’ render from your rgb image - this will get your foreground elements against a black background.

  3. Copy the alpha mask into the alpha channel of your image.

  4. Composite away!

If you’re using photoshop, the process is a little more complicated:

  1. Render out a standard, full colour (rgb) image, an alpha mask, and a ‘multipass’ render containing the layer ‘background’ from vue. DON’T do any post-process exposure adjustment of any kind, and don’t compress the files.

  2. Subtract the ‘background’ render from your rgb image (image>apply image) - this will get your foreground elements against a black background. Save this image as ‘foreground’.

  3. Load the custom background image you would like to use (This will be on the canvas of a new file).

  4. Paste your alpha image into layer 1 of this new file.

  5. Invert it.

  6. Set layer 1 to ‘multiply’

  7. Paste your ‘foreground’ image you saved earlier into layer 2.

  8. Set this to ‘linear dodge (add)’

Hope that all makes sense - I just tried it with a simple vue scene (with trees) and it worked fine. I initially had problems because I’d accidentally turned on ‘auto exposure’ - BAD IDEA.

AJ

#6

Can’t you fix it inside Vue? I would like to do so, but I’m gonna try the above solution…

#7

I know it seems odd, but Vue isn’t actually doing anything wrong. Alpha channels are MEANT to work like this.

Admittedly, the whole process might be easier if it was possible to render an image from vue without the sky - i.e. if there was a render option ‘don’t render sky’ or something similar. However, since it’s possible to render the sky separately (as described above), the workaround is relatively simple.

Note that I’ve edited the above process a little - I was being lazy and using the ‘difference’ blend mode instead of the more mathematically correct ‘subtract’. In most normal vue renders (where the sky is lighter than the ground) it probably won’t make any difference at all (it didn’t in my test scene), but the ‘correct’ version should be up there…

Did you get everything to work okay?

AJ

#8

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