Photoshop CS2 and Multiple Alpha Layers

OK, I'm begging for help here. I'm having some serious problems with photoshop CS2 and multiple alpha layers. I certainly know how to create an alpha layer. I know how to make multiples of them and turn them on and off with the little eyeball thingamabob. Where I'm getting balled up is that it seems that when I save to any flat file, it does not matter which layers I had visible at the time of save, they are all binary OR'd together (if any pixel in any layer is white, then the result is fully visible alpha) whether or not that layer was enabled at the time of save.

Am I losing my mind?

Of course you are. Since there's no such thing as an "alpha layer", it would be impossible not to have problems trying to make them. If you want to talk about alpha CHANNELS though, let's do that.


You do? I don't. I also don't know how to extract green cheese from the moon, how to breed chocolate cows for chocolate milk, or how to turn lead into gold. If you figure any of those things out, be sure and let me know. In the mean time, let's talk about things that actually do exist, alpha channels, not alpha layers.




I'd really like to help you, but I'm sorry to say I'm having a very difficult time figuring out what you're talking about. First, what does "all binary OR'd together" mean?

Second, are you in fact actually talking about multiple layers or multiple channels? The answer to that will make all the difference in the world toward solving your problem.

If you are talking about channels, then the behavior you describe would be normal. If you've got more than 4 channels in your working image, then a TGA outputted from that image will be reduced to 4, as that is the maximum number of channels that the TGA format supports. The first three, which always govern color, will be left in act, and the fourth, the one that governs transparency, will be created by compositing all the extra channels together. In such cases, Channel 4 will always come out completely white, ALWAYS.

To prevent this and other problems from happening, make sure you always have one, and only one, (properly created) alpha channel in place at the time of TGA output. Never try to put more than 4 channels into a TGA.

And remember, as you discovered, it doesn't matter whether a particular channel happens to be turned on or off in the GUI at the time of save. If it is present, it is part of the image, period.

If you are talking about layers though, then I'm afraid you'll need to re-explain what you mean in terms we can all understand.

Third, when you say "save to any flat file", do you mean you're flattening your layered images prior to save, or are you simply noting that TGA files are inherently flat? If it's the former, stop doing that. It's destructive and it yields no benefit whatsoever. Always preserve your layered work as a PSD first, and then save out to TGA as a copy afterwards.

I don't know if this is any use, or even the best way to go about it (I'd like to hear other methods if not). If you need to save multiple .tgas from your one .psd, each with a different alpha channel, I find it handy to copy the contents of each channel you make onto a seperate layer (hidden, obviously). Then if you need to come back to the file and change it, you can copy the appropriate layer and paste it back into the alpha channel. That way you can keep all that information in a safe place and it won't interfere when you're trying to save yer 32 bit dealie.

Helpful if your alphas are made up from a bazillion different layers or tricky selections, which mine invariably are. My working practice is less of a 'flow' and more of a 'devastating explosion'*.



*with an occasional lone survivor

*laughs*

Oooh, I soooo should've known better given that I've read your other posts on the layers/channels issue.

I think you've answered my other questions. The bottom line is independent of whether you have marked a channel as visible, the photoshop exporter to some non-native format that supports transparency does not take that into account. So no, you may not have more than 1 alpha channel.

I'm assuming then, that if I want to have a single file with the ability to export with different transparency settings, what I need to do is encode the alpha information on a layer (*laughs* see, I can learn), then have the action cut&paste the pixels in that layer to the one and only alpha channel I get.

Is it just me or is this counter-intuitive? It would make sense to say that the exporter exports using whatever the currently in-use alpha channel is.

Perhaps my terminology wasn't shiny enough, but that was pretty much what I was saying You may find things a bit easier if you save yourself the effort of encoding the alpha information and just copy and paste it instead

Hehehe.


Other formats may take it into account, but TGA won't. If you're a TGA, all you know is there are 3 channels for color, and sometimes there's a fourth for SOMETHING else. Determining the something to mean transparency or anything else is the job of the destination program, which in this case, is SL. The TGA itself doesn't actually know what transparency is.


Exactly. Notice the Linden clothing templates come with sample alphas stored on hidden layers. That's why.

Come to think of it, that's probably where the dreaded "alpha layer" term comes from. People probably download those templates, see layers called "alpha", and then naturally assume that there must be such a thing as an "alpha layer".


It is counter-intuitive if you're thinking in terms of PSD or some other format that supports an unlimited number of channels. If you're thinking in terms of TGA though, which predates the modern PSD by a couple of decades, it does make sense. If you begin with the end in mind, you wouldn't think of putting more than 4 channels into a TGA-destined image.