[gdal-dev] Calibrating colors of a series of maps

Jan Hartmann j.l.h.hartmann at uva.nl
Sat Dec 26 10:56:26 EST 2009


I put the following question on the GRASS user list. It isn't possible 
with GRASS (or the programs mentioned by Glynn), but if someone on this 
list can help me further, I would be very grateful. I have been 
struggling for some time with this problem, and I'll have to process 
lots of scanned old maps in the near future.


Jan Hartmann wrote:

> >  I am working with series of old topographical maps, ranging from 10 to
> >  600 map sheets per map. Each sheet is discolored a bit from age. How can
> >  I process a complete series in such a way that there are no differences
> >  visible any more between map sheets? Preferably I would like to
> >  downsample them to 8 bits color table, as the originals only have a
> >  small set of colors. In other words: how do I calibrate set of maps to
> >  the same optimal color table?
This is probably better done with general image-processing software,
e.g. pnmquant (from the Netpbm package) or "convert -colors ..." (from

-- Glynn Clements <glynn at gclements.plus.com>

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