[Gdal-dev] gdal_merge.py Gtiff files with -pct losing color

[Dori]

Frank,

I reported the bug the best I could: 1384.

Matt and Frank,
I certainly appreciate all the help I have received from both.
I hope to be able to give something back to GDAL soon.

Tx

On 12/7/06, Frank Warmerdam <warmerdam at pobox.com> wrote:
>
> Matt Wilkie wrote:
> > Hi Dori, gdal doesn't like something about the way the source image[1]
> > is formatted. I can't view it in OpenEV or in QGIS, it just comes up as
> > a black image even before trying to translate or merge. Histograms in
> > both programs come up blank.  You should probably file a bug[2]
> >
> > In the meantime, I was able to open the image using ossim
> > imagelinker[3], so maybe give that a try (though being pressed for time
> > you may not have the time to learn it).
> >
> >
> > [1]
> >
> http://www.mediamax.com/izzybitsie/Hosted/AS_GMSNO_00_20061122205548.tif.gz
> > [2] http://bugzilla.remotesensing.org/enter_bug.cgi?product=GDAL
> > [3] http://www.ossim.org/OSSIM/Welcome.html
>
> folks,
>
> I'm afraid I lost track of this thread.  I have now fetched the file and
> inspected it.  TIFF colors maps are supposed to have colors in the
> range 0-65535 for each component instead of the usual 0-255 in other
> formats.  It seems that this file has been incorrectly generated to
> have the colormap between 0 and 255.  So when GDAL converts it to
> 0-255 values (roughly by dividing by 256) everything ends up black.
>
> So, the input files are screwed up.
>
> Any programs that ignore colormaps will just treat the images as
> greyscale.
>
> I also think this may be a fairly common failure with tiff generators
> and that some applications may have special logic to look for files
> with all colormap values in the 0-255 range and avoid the rescaling
> that should happen.
>
> Dori - if you want to file a bug in the GDAL bugzilla (Matt provided
> the link above) for this problem, I'll try and implement a "hack" so
> that these PCTs work properly.  It would be nice to get this in place
> in time for beta2.
>
> Best regards,
> --
>
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | President OSGeo, http://osgeo.org
>
>
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