[Ubuntu] imagemagick & gdal ?

[Frank Warmerdam]

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,
-- 
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