NoColor tag in GeoTiff

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NoColor tag in GeoTiff

David Strip
I've got some geotiffs with NoColor tags in the headers that I want to
edit. (The nocolor tag is listed by gdalinfo)
I use listgeo to capture the header, then strip the header with tiffcp.
I've tried editing the resulting tiff with a variety of editors
(including Photoshop and Windows Paint) and the the no data/no color
areas appear light cyan in all the editors.
I then add the geo headers back to the edited tiff using geotifcp -g.
If I open the resulting geotiff in OpenEV, the no color pixels are now
light cyan, not no data.
It appears there's a NoColor tag in the geotiff that does not get copied
by listgeo, then goes unrecognized by the various editors, and since it
wasn't listed by listgeo, it's not restored by geotifcp.

Are NoColor tags standard tiff headers?
This website - http://www.awaresystems.be/imaging/tiff/tifftags.html -
ostensibly lists the registered tags, and nocolor is not one of them.
Are they unique to geotiff?
Should listgeo/geotifcp copy/restore these?
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Re: NoColor tag in GeoTiff

Frank Warmerdam
David,

I'm guessing that when you refer to "NoColor" this is what I normally
think of as
the NODATA value.  The GDAL tag used for this is documented on the Aware
Systems web site under private tags:

http://www.awaresystems.be/imaging/tiff/tifftags/gdal_nodata.html

The tag is define with regard to GDAL and is not part of the GeoTIFF
specification.

Best regards,

On Fri, Mar 2, 2012 at 8:20 PM, David Strip <[hidden email]> wrote:

> I've got some geotiffs with NoColor tags in the headers that I want to
> edit. (The nocolor tag is listed by gdalinfo)
> I use listgeo to capture the header, then strip the header with tiffcp.
> I've tried editing the resulting tiff with a variety of editors
> (including Photoshop and Windows Paint) and the the no data/no color
> areas appear light cyan in all the editors.
> I then add the geo headers back to the edited tiff using geotifcp -g.
> If I open the resulting geotiff in OpenEV, the no color pixels are now
> light cyan, not no data.
> It appears there's a NoColor tag in the geotiff that does not get copied
> by listgeo, then goes unrecognized by the various editors, and since it
> wasn't listed by listgeo, it's not restored by geotifcp.
>
> Are NoColor tags standard tiff headers?
> This website - http://www.awaresystems.be/imaging/tiff/tifftags.html -
> ostensibly lists the registered tags, and nocolor is not one of them.
> Are they unique to geotiff?
> Should listgeo/geotifcp copy/restore these?
> _______________________________________________
> Geotiff mailing list
> [hidden email]
> http://lists.maptools.org/mailman/listinfo/geotiff



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