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

[Robert Sanson]

Hi Jason
 
Well, ECW use wavelet compression, which is lossy, and data values can get changed slightly.
 
regards,

Robert

>>> Jason Beverage <jasonbeverage at gmail.com> 16/03/2010 10:27 a.m. >>>
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
_______________________________________________
mapserver-users mailing list
mapserver-users at lists.osgeo.org 
http://lists.osgeo.org/mailman/listinfo/mapserver-users 





------------------------------------------------------------------
The contents of this email are confidential to AsureQuality. If you have received this communication in error please notify the sender immediately and delete the message and any attachments. The opinions expressed in this email are not necessarily those of AsureQuality. This message has been scanned for known viruses before delivery. AsureQuality supports the Unsolicited Electronic Messages Act 2007. If you do not wish to receive similar communications in future, please notify the sender of this message.
------------------------------------------------------------------



This message has been scanned for malware by SurfControl plc. www.surfcontrol.com ( http://www.surfcontrol.com/ )





Click here ( https://www.mailcontrol.com/sr/D7!VF8Wy1bvTndxI!oX7UnIFdu++nxPn8TyWuTsECDRa2Inu1mF0RyIAxMxkdMyGu1AQC+ell+VjEfBJ2k7YZA== ) to report this email as spam.
------------------------------------------------------------------
The contents of this email are confidential to AsureQuality. If you have received this communication in error please notify the sender immediately and delete the message and any attachments. The opinions expressed in this email are not necessarily those of AsureQuality. This message has been scanned for known viruses before delivery. AsureQuality supports the Unsolicited Electronic Messages Act 2007. If you do not wish to receive similar communications in future, please notify the sender of this message.
------------------------------------------------------------------
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/mapserver-users/attachments/20100316/bb90c48d/attachment.html