Kevin Turner wrote:

> <snipped...>

> Thing is, gimp does erase/clear by setting the alpha component to fully
> transparent, but doesn't touch the other channels.  So you can load up
> that image again, move the alpha channel back to opaque, and the
> background you erased comes back in full detail.
> This isn't a bug,

True  <snippage...>

> The "GIMP That's Smarter Than You
> Are" (sponsored by the Corporation for Using Technology to Further Human
> Inferiority Complexes) could detect this fairly trivially, and ask if
> you really meant to be saving that stuff.  The semi-lossy filter could
> be as simple as this mathmap[1] filter:
> if alpha(origVal(xy)) == 0 then rgba:[0,0,0,0] else origVal(xy) end


IMHO, this is ninety-five percent a documentation problem.
(1) Much of Gimp treats the 'A' as just another color component
(some parts don't) and if there is high information content in
R, G, B, then - among other things - lossless compression won't
compress much.
(2) I trust the user in choosing between information
content and compression, so long I walk the mile in telling her
that this is a choice to be considered. Then she can write/invoke the
macro or deliberately set R = G = B = A = 0  in all regions deemed
transparent before writing out to file.
(3) If someone wants to write something in Gimp core or the png
plug-in to automagically clean up after the user, it's presence should
be made known and its activation optional.

My two cents.
Be good, be well

Garry Osgood

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