Outputting alpha channel only

[brammelo]

Group your scene.
Add a composting tag to group.
Choose a buffer number (1, for instance)
Activate Multi-Pass in Render settings.
Add Object Buffer to the list and select the correct group ID (1, in this case)
Indicate the type of file you want
And finally: render.

Cheers,
BaRa

[bov]

Hi BaRa, I've grouped the objects so that they are in a 'null object' I then added a 'render' tag and checked the ‘compositing background’ box and checked the 'ID 1' object buffer box. When I added 'object buffer 1' in the Multi-Pass part of the settings and tried to render the grouped object became a silhouette but the white wasn't white it was a light gray. Do you have any idea what I'm doing wrong?

Bov

[brammelo]

Are you working with transparent objects?

[bov]

Yes - I also have a null object inside a null object. The grey I mentioned before happened when I quickly tried out things using default cubes. The actual objects are transparent objects inside a null object which itself is in a null object.

Bov

[brammelo]

I tried the same here, and according to PS, it's 100% black and white.

The grey area's are only there when you're using transparent materials on objects, which makes sense.

Are you sure you didn't use the rendered standard image instead of the alpha? Is "save image as" still active? If it is, then deactivate it.

[bov]

I think with your help I found a work around. It's not exactly what I wanted but I think I can work with it. I wanted the alpha as an AVI. What I’m doing now is just stripping the scene and leaving the object I want. I then used the 'Blend channels' (checking all the boxes) in the 'multi-past' section and just output a tiff sequence. I also checked two the alpha boxes in the 'save' section. I know there is a simpler way of doing it, but unfortunately time isn't on my side. Thanks for your help; you pointed me in the right direction.

Cheers, Bov

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