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Nangleator
07-23-2008, 02:12 PM
I love the idea that TIFs and Targas and PNGs can have their own alpha channels, but how come they aren't used by default?

I'd like to load an image, map it to a flat plane, and if there's an embedded alpha, then it's automatically used as a transparency map.

I don't like creating an instance of the image in the image editor, applying "Alpha Only" to it, and manually setting the clip map or transparency map.

And here's my real question. What's the difference between "Alpha Channel: Enabled" and "Alpha Channel: Disabled"? I submit there is no difference at all.

Lightwolf
07-23-2008, 02:19 PM
The alpha channel is used by default when you layer the image onto a single surface channel. I.e. to place a number of decals on a single surface.

Which also explains the difference between the two alpha options.

Cheers,
Mike

Nangleator
07-23-2008, 02:35 PM
Oh.

Well, that's useful, too, I guess. I do logos and try to composite product images far more often, though. That's why I've never discovered that.

Thanks!

Lightwolf
07-23-2008, 02:38 PM
Oh.

Well, that's useful, too, I guess. I do logos and try to composite product images far more often, though. That's why I've never discovered that.

Thanks!
You're welcome.

Looking at it from another angle: Imagine you place an image onto your colour channel... and it modifies your transparency as well. Behind your back (since you're working on the colour!).

Cheers,
Mike

LFGabel
09-11-2008, 12:24 PM
However, it doesn't do exactly as what I would want. I'm working on getting a light trail effect with prerendered travelling light animation. I'm still on 8.5, so this might be fixed, but... if you map a prerendered image (with alpha) onto a surface:

- it does not appear in your new rendered image alpha.
- it dulls down your previously prerendered image, since it is applying an alpha to an image that already has one.

This pretty much makes them useless for what I need them for.

Even after taking the prerendered image, unpremultiplying it, then using that with it's alpha in the transparency image results in a washed out image.

The only way I was able to make it work is to apply the prerendered image without alpha, render out a new sequence over black (without alpha) to be comped over top of the plate.

Then in the comp app, take the luminosity of the images, use that as the alpha and comp with the plate, unpremultiplied. That worked.

Nangleator
09-11-2008, 01:04 PM
Brain. Hurts.