On Mon, Sep 12, 2005 at 06:04:59PM -0400, michael chang wrote:
> On 9/12/05, Diaa Sami <[EMAIL PROTECTED]> wrote:
> > actually I need to do this with 24-bit PNG's, is it possible?
> > it it's not, do u know any other free tool that does this?
> AFAIK GIMP doesn't support 24-bit colour.  Apparently it's a
> limitation in GIMP's current design, and won't be fixed for a long
> time.

Apparently, my e-mail from before didn't go out)

GIMP definitely supports 24-bit color.  This is 8-bits per channel (R,G,B).
With an Alpha channel (more on that later) that is 32-bit color.  GIMP does
not support 16-bit per channel (48/64 bit color).

Now that that is cleared up.

Diaa, I have read your e-mail several times, and I don't have a clue what
you are trying to do.  Perhaps some clarification would be in order?  I'm
very familiar with the PNG format, having written and ported
encoders/decoders for various projects.

You can do binary transparency with 24-bit PNGs by thresholding the alpha
channel.  This will leave you with just on and off (255 and 0).  This is
Layer -> Transparency -> Threshold Alpha

If you want to convert a color to transparent, you want
Layer -> Transparency -> Color to Alpha

If what is really happening, is that your application has the old hack where
a certain color represents transparent (usually olive or magenta), then just
draw that color in the bits that you want transparent.  It is up to your
application to then render that color as transparent.  


Computer Science is as much about computers as astronomy is about telescopes
        -- Edsger Wybe Dijkstra (1930-2002)
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