Patrick McFarland <[EMAIL PROTECTED]> wrote:

>> Conceptually, I agree that alpha = 0 means that the RGB value of the pixel
>> is undefined. Alpha = coverage; coverage = 0 means no pixel is there. Gone.
>> Inexistent. On the other hand, mask = 0 does NOT mean that the corresponding
>> pixel is inexistent, as we already agree (I think).
>Its only inexistant to the calculations. The RGB data doesnt go away, which is
>what I think you mean. 

I mean "conceptually" as I emphasize in my quote above. It's never actually
inexistant; there are bytes that hold values for R, G and B and the value of
a byte is always defined and existant.

>I think that all the alpha and transparency mask operations should be folded in
>to just doing transparency mask, and then alpha on load be converted to
>transparency masks.

That's equivalent to just use alpha and treat it as a channel just like R, G
and B are, letting the user to paint in the channel, as I already suggested.

>GIMP is exactly the same way. I have no way of doing alpha only operations,
>except when hacking up the transparency mask.

Wrong. You can manipulate the Alpha channel by using Levels, Curves,
Histogram and even Threshold Alpha. The latter requires a separate plug-in,
though, since the Threshold tool does not work with the Alpha channel even
if it does with the R/G/B ones. And there's of course the eraser and its
controversial counterpart anti-erase tools.

>In addition to this, it should be possible to copy a transparency mask to a
>RGB layer, something GIMP doesnt support afaik. (Which, then, it would appear
>as a greyscale image)

Copy and Paste works in 1.3 for this task. In 1.2 you can Paste as New, then
copy again in the new image and paste back in the original image.

  Pedro Gimeno
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