Fw: [Mapserver-users] transparent background raster (tif)

[Frank Warmerdam]

Rosangela Silva wrote:
>  Hello,
> 
>  I'm using mapserver 3.6.5.
>  I don't know how the mapserver interprets the background of the
>  tiff or jpg images. I'm looking for information about it, and some
>  softwares assumes the transparent background like a cannel "alpha",
>  but I don't know exactly how it works.
>  Sorry, but, for while, it is everything I know to explain.

Rosângela,

How it is accomplished will, as Ed suggests, depend on the nature of the
image.  MapServer 3.6.5 (if using GDAL for raster IO) will support treating
pixels with "alpha=0" as transparent if the image is RGBA.  If the image is
in a format that returns a "nodata" value, or knows that particular color
indexes in a paletted image are transparent, they will be automatically
treated as transparent.  3.6.x does *not* support the user indicating a
particular RGB value as transparent for 24bit inputs, but the OFFSITE value
can be used to mark one raw pixel value for greyscale or paletted images
that should be treated as transparent.

I hope this helps.

Best regards,

-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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