transparent overlay and alpha blending

[Frank Warmerdam]

On 10/6/05, Jerl Simpson <jerl.simpso at gmail.com> wrote:
> Hello,
>
>  I'm not sure if I'm posting the right place or not,but here goes.
>
>  I use Mapserver to generate maps (of course)  I have another program that
> grabs these maps, adds some dynamic content, and spits them out to a
> browser.  The other program is a C program and uses the GD library to
> manipulate the images.
>
>  My output format is:
>
>    OUTPUTFORMAT
>      NAME gif
>      DRIVER "GD/GIF"
>      MIMETYPE "image/gif"
>      IMAGEMODE RGBA
>      EXTENSION "gif"
>    END
>
>  So I should be able to support alpha blending.
>
>  The problem, is when I add my layer to this gif, the area that should be
> blended is completely opaque.
>  I can't seem to find anywhere where this reverts to a paletted image, so
> I'm lost.
>
>  If anyone can help me, I'd be greatly appreciative.
>
>  I realize there's not much information to go on, so I'll wait to hear from
> someone before sending specific information.

Jerl,

There is no such thing as an RGBA (or RGB) GIF file.  Ideally
MapServer would realize this (sooner) and blow a gasket when
it encounters your OUTPUTFORMAT declaration.  If you submit
a bug report and see that it is assigned to me I'll try and fix that.
If you want RGB or RGBA output format use a format that supports
it like PNG.

Best regards,
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent