[mapserver-users] Average/Bilinear Resampling and Alpha Bands

[Jason Beverage]

Hey again,

Some more information, the file I was using was an ECW I converted from a
tif.  The black splotches appear if I use the ECW, but if I use the original
tif file I don't see them.

However, when using AVERAGE or BILINEAR, it appears as if the alpha values
are either completely transparent or completely opaque.  The image I'm using
is an image I used the gdalwarp -cblend option on to do some polygon cutting
so I'm losing my blending line if I do average or bilinear resampling.  I'll
see if I can create a small example that shows the issue.

Thanks,

Jason

On Mon, Mar 15, 2010 at 3:55 PM, Robert Sanson <SansonR at asurequality.com>wrote:

>  Hi Jason
>
> That's not unexpected. RESAMPLE=NEAREST preserves the "nodata" vales used
> in the mask. BILINEAR or AVERAGE combine values from adjoining pixels, so
> the "nodata" pixels get some other value.
>
> regards,
>
> Robert
>
> >>> Jason Beverage <jasonbeverage at gmail.com> 16/03/2010 4:53 a.m. >>>
>
> Hi all,
>
> I have some imagery that is in UTM that contains an alpha band that
> masks out areas with no data.  When I use MapServer to reproject it to
> epsg:4326, the masked out area looks good if I set RESAMPLE=NEAREST on
> the layer.  If I change the RESAMPLE option to BILINEAR or AVERAGE I
> get black splotches in the area that is transparent.
>
> Has anyone else seen this behavior?
>
> I'm using MapServer 5.6.1
>
> Thanks,
>
> Jason
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