[mapserver-users] MapServer 5.2.1 - Trying to show a band as transparent

[Frank Warmerdam]

On 11-05-31 03:31 PM, Eduardo Kanegae wrote:
> Hi,
>
> I have a Windows 2008 R2 Server running MapServer 5.2.1 from MS4W pack.
>
> My trouble: I´m trying to display a gdaltindex file ( set of rasters ) but the
> image border is not being displayed as expected.
>
> The raster files are all 4-band based, with 3 bands for RGB and the 4th band
> for ALPHA channel.
> The band 4 has only two possible values: 0 ( for transparent desired area) and
> 255 for area where RGB bands has content
...
> ...
> OPACITY ALPHA

Eduardo,

I am not clear on what "OPACITY ALPHA" is supposed to do.  I don't think
you need it.

> ...
> PROCESSING "BANDS=1,2,3,4"
> PROCESSING "SCALE_1=AUTO"
> PROCESSING "SCALE_2=AUTO"
> PROCESSING "SCALE_3=AUTO"
> PROCESSING "SCALE_4=1,2"
> PROCESSING "RESAMPLE=BILINEAR"

SCALE_4=1,2 will transform 1 to 0, and 2 to 255 but the input values are
apparently 0 and 255 already (as I deduce from the qgis snapshot) so I think
you should just omit the SCALE_4 processing option.

There may be bad interactions between RESAMPLE=BILINEAR and the alpha
support.  You might want to try with and without this option.   If this is
an issue try upgrading to MapServer 6 and see if the problem persists.  I
have made significant improvement in raster alpha handling in recent years.

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