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

[Oliver Christen]

Hello Tomas

as far as I can see the tiff are already in RGBA, from what I can see 
from the gdalinfo (see below)

I tried using OFFSITE, but I couldnt see any difference in the output 
with or without it.

In my opinion something is going wrong in the image treatments when a 
resampling is applied, as if the alpha transparency value for the border 
pixels was not preserved during the processing.
but then that's pure speculation.


Warning 1: TIFFReadDirectory:Unknown field with tag 37724 (0x935c) 
encountered
Driver: GTiff/GeoTIFF
Files: 592116.tif
        592116.tfw
Size is 5020, 5020
Coordinate System is `'
Origin = (2591997.899999999906868,1117002.100000000093132)
Pixel Size = (0.200000000000000,-0.200000000000000)
Metadata:
   TIFFTAG_SOFTWARE=Adobe Photoshop CS2 Windows
   TIFFTAG_DATETIME=2013:04:18 14:52:47
   TIFFTAG_XRESOLUTION=72
   TIFFTAG_YRESOLUTION=72
   TIFFTAG_RESOLUTIONUNIT=2 (pixels/inch)
Image Structure Metadata:
   INTERLEAVE=PIXEL
Corner Coordinates:
Upper Left  ( 2591997.900, 1117002.100)
Lower Left  ( 2591997.900, 1115998.100)
Upper Right ( 2593001.900, 1117002.100)
Lower Right ( 2593001.900, 1115998.100)
Center      ( 2592499.900, 1116500.100)
Band 1 Block=5020x1 Type=Byte, ColorInterp=Red
   Mask Flags: PER_DATASET ALPHA
Band 2 Block=5020x1 Type=Byte, ColorInterp=Green
   Mask Flags: PER_DATASET ALPHA
Band 3 Block=5020x1 Type=Byte, ColorInterp=Blue
   Mask Flags: PER_DATASET ALPHA
Band 4 Block=5020x1 Type=Byte, ColorInterp=Alpha

> Hi Oliver,
>
> Are you using mapserver's OFFSITE parameter, and/or do your tiff files 
> have a nodata pixel set ?
> What happens if you convert your tiff to 32bit RGBA? (Not suggesting 
> this is a valid workaround, just trying to narrow down the reasons for 
> this).
>
> --
> thomas
>
>
> On 18 April 2013 15:27, Oliver Christen 
> <oliver.christen at camptocamp.com 
> <mailto:oliver.christen at camptocamp.com>> wrote:
>
>     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
>
>
>
>     -- 
>     Camptocamp SA
>     Oliver Christen
>     PSE A
>     CH-1015 Lausanne
>
>     www.camptocamp.com <http://www.camptocamp.com>
>
>     +41 21 619 10 23 <tel:%2B41%2021%20619%2010%2023> (direct)
>     +41 21 619 10 10 <tel:%2B41%2021%20619%2010%2010> (centrale)
>     +41 21 619 10 00 <tel:%2B41%2021%20619%2010%2000> (fax)
>
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>
>


-- 
Camptocamp SA
Oliver Christen
PSE A
CH-1015 Lausanne

www.camptocamp.com

+41 21 619 10 23 (direct)
+41 21 619 10 10 (centrale)
+41 21 619 10 00 (fax)

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