[mapserver-users] geotiff resampling and transparency - artifact problem

[Oliver Christen]

dear all

Im having some issue when applying PROCESSING "RESAMPLE=AVERAGE" or 
"RESAMPLE=BILINEAR" on some geotiff with transparency.
Either a clear or dark artifact appears on the border of the image, as 
seen on these examples:

http://dev.camptocamp.com/files/mapserver/fuzzy_edge_AVERAGE.png
http://dev.camptocamp.com/files/mapserver/fuzzy_edge_BILINEAR.png

if I specify no PROCESSING at all, the transparency is correct (but not 
the image "quality" which I wanted to improve with the PROCESSING ):
http://dev.camptocamp.com/files/mapserver/fuzzy_edge_NOPROCESSING.png

at first I though the problem may have been caused by a fuzzy edge on 
the transparent edges in the geotiff:
http://dev.camptocamp.com/files/mapserver/fuzzy_edge.png
so I retreated one image to have clean edges:
http://dev.camptocamp.com/files/mapserver/clean_edge.png

but I couldnt see much difference in the result:
http://dev.camptocamp.com/files/mapserver/clean_edge_AVERAGE.png
http://dev.camptocamp.com/files/mapserver/clean_edge_BILINEAR.png

there is no visible artifact for all border multipe of 90° (horizontal 
and vertical edges), only the non 90° edges show that problem.

Im not knowledgeable with image manipulation and resampling with 
transaprency, so I dont know if this is normal or not.

Any idea if there is some way to "solve" this "problem" ?

thank you for your attention

best regards
Oliver



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Camptocamp SA
Oliver Christen
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