On 12-04-21 07:32 AM, Heikki Julkunen wrote:
First, thanks all for a great set of tools!
Anyway, I've seen this mentioned in a post elsewhere, but there was no reply.
I'm not sure who to 'blame', gdal or imagemagick, but it seems like the alpha
channel
embedded by imagemagick is NOT compatible with gdal. The transparency is NOT
used.
(since imagemagick has no clue about geo-data after image processing I use
geotifcp to add that).
Example: gdalinfo bad-example.tif
<<geo meta removed>>
Band 1 Block=10020x1 Type=Byte, ColorInterp=Red
Band 2 Block=10020x1 Type=Byte, ColorInterp=Green
Band 3 Block=10020x1 Type=Byte, ColorInterp=Blue
Band 4 Block=10020x1 Type=Byte, ColorInterp=Undefined
A working file looks like this:
gdalinfo good-example.tif
<<geo meta removed>>
Band 1 Block=10020x1 Type=Byte, ColorInterp=Red
Mask Flags: PER_DATASET ALPHA
Band 2 Block=10020x1 Type=Byte, ColorInterp=Green
Mask Flags: PER_DATASET ALPHA
Band 3 Block=10020x1 Type=Byte, ColorInterp=Blue
Mask Flags: PER_DATASET ALPHA
Band 4 Block=10020x1 Type=Byte, ColorInterp=Alpha
I.e, it seems like the alpha from imagemagick is global but gdal expects a per
dataset alpha ?
Heikki,
This would likely be better pursued on the gdal-dev mailing list, but it
is not possible to evaluate without seeing the tiffinfo report for the
file in question. It may be an "associated" vs. "unassociated" alpha
problem.
Best regards,
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up | Frank Warmerdam, [email protected]
light and sound - activate the windows | http://home.gdal.org/warmerda
and watch the world go round - Rush | Geospatial Software Developer
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