On Tue, Sep 13, 2005 at 05:30:21PM +0300, Diaa Sami wrote:
> that's exactly what I wanted, I looked into PNG docs, and I found out 
> that there are two functions responsible for this, which are 
> png_get_tRNS and png_set_tRNS.

Yup.  For just about any chunk, there is a get/set pair in the reference
implementation.  The GIMP could easily figure out when the alpha is binary
(to use tRNS rather than RGBA), but picking out an unused color to represent
transparent that is acceptible to the user, applications, and further
editing is an impossible (or difficult) task.

IE ignores tRNS when you aren't in palette mode, anytime you added some of
that color to an image, it would turn transparent seperate from what you
expect, etc.

> ok, I'll use ImageMagick to do it.

Glad I could help.

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

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