PS is filling my alpha channel

HT
Posted By
harry_teasley
Aug 3, 2004
Views
283
Replies
4
Status
Closed
I’m saving 32-bit TGAs out with empty alpha channels (every pixel of alpha set to 0) — I have to, don’t ask why, the reason is excellent despite what you may initially think — and every time PS loads them, they load with completely opaque alpha channels (every pixel set to 255). I know the alpha is empty on save, and changed on load, because the way it behaves after I’ve emptied the alpha channel and saved it.

Why is this happening? Does this happen for anyone else? This is not desirable behavior. I’d like PS to not do this.
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alpha channel fill

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Scott_Falkner
Aug 3, 2004
What happens if the Alpha channel is non-empty? Is Photoshop inverting the channel? I’m guessing you need the channel for use in some other program. If so, how does the image open there? Is PS changing the channel on save or on open?
HT
harry_teasley
Aug 3, 2004
It’s changing the channel on open. It saves correctly. I’ve confirmed that PS 7 does this as well.

If the channel is not empty, it does not alter the channel. Only if the channel is completely empty, then it will completely fill it on open.

I’ve confirmed this behavior on other installations as well: I don’t think it’s just me.
CC
Chris_Cox
Aug 4, 2004
Are you using an alpha channel, or transparency?
HT
harry_teasley
Aug 4, 2004
I’m using an alpha channel: I explicitly create it via the Channels palette (I’m one of the old-school TGA fans, who griped about the 7.0 TGA handling with regards to transparency and alpha).

It’s trivial to replicate this bug:

1. File > New.
2. Channels Palette > New.
3. File > Save. Choose TGA, 32-bit.
4. File > Close.
5. File > Open <filename>.

The formerly empty alpha channel will be full. It is empty on save, and is saved correctly. It’s just altered on open within PS.

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