[gdal-dev] failing in making transparency

[Chaitanya kumar CH]

ahmet,

One likely reason for the dark image is that your viewer is assuming a range
of 0-65535 for the alpha values.
Check the histogram of the output image. In the histogram for the second
band, there should be a bunch of 0 valued pixels and 255 valued pixels.
Please provide a small sample image if the problem persists.


2011/2/6 ahmet temiz <ahmettemiz88 at gmail.com>

> hello
>
> I want to make nodata areas transparent.
>
> here is what I did:
>
> 1.
> $gdalinfo  -mm -noct duy_cat1.tif | grep -i 'nodata'
>  NoData Value=65535
>
> 2.
>  gdalwarp  -srcnodata 65535  -dstalpha duy_cat1.tif duy_cat14.tif
>
> But, duy_cat14.tif looks full black
>
> here is info of  outputfile(duy_cat14.tif):
> ~~~~~~~~~~
> Driver: GTiff/GeoTIFF
> Files: duy_cat14.tif
> Size is 4677, 5527
> Coordinate System is:
> PROJCS["UTM Zone 36, Northern Hemisphere",
>    GEOGCS[,
>        DATUM["unknown",
>            SPHEROID["unnamed",6378388,297.000000000005]],
>        PRIMEM["Greenwich",0],
>        UNIT["degree",0.0174532925199433]],
>    PROJECTION["Transverse_Mercator"],
>    PARAMETER["latitude_of_origin",0],
>    PARAMETER["central_meridian",33],
>    PARAMETER["scale_factor",0.9996],
>    PARAMETER["false_easting",500000],
>    PARAMETER["false_northing",0],
>    UNIT["metre",1,
>        AUTHORITY["EPSG","9001"]]]
> Origin = (437192.936421879974660,4649982.939232329837978)
> Pixel Size = (20.004039786776190,-20.004039786776190)
> Metadata:
>  AREA_OR_POINT=Area
> Image Structure Metadata:
>  INTERLEAVE=PIXEL
> Corner Coordinates:
> Upper Left  (  437192.936, 4649982.939) ( 32d14'30.03"E, 41d59'55.01"N)
> Lower Left  (  437192.936, 4539420.611) ( 32d15'11.54"E, 41d 0'10.24"N)
> Upper Right (  530751.831, 4649982.939) ( 33d22'16.70"E, 42d 0'1.87"N)
> Lower Right (  530751.831, 4539420.611) ( 33d21'56.38"E, 41d 0'16.87"N)
> Center      (  483972.383, 4594701.775) ( 32d48'28.68"E, 41d30'10.99"N)
> Band 1 Block=4677x1 Type=UInt16, ColorInterp=Palette
>    Computed Min/Max=0.000,65449.000
>  Color Table (RGB with 65536 entries)
> Band 2 Block=4677x1 Type=UInt16, ColorInterp=Alpha
>    Computed Min/Max=0.000,255.000
> ~~~~~~~~~~~
>
> could you tell me where the problem is ?
>
> regards
> --
> Ahmet Temiz
> Jeoloji Müh.
> Planlama ve Zarar Azaltma Dairesi Başkanlığı
> Bilgi ve CBS grubu
> Eskişehir Yolu 10. km.
> Lodumlu / Ankara
> Tel : 0 312 2872680 / 1535
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>



-- 
Best regards,
Chaitanya kumar CH.
/tʃaɪθənjə/ /kʊmɑr/
+91-9494447584
17.2416N 80.1426E
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