[Geotiff] Geotiff List: Tool to convert 8-bit gray to RGBA using a custom color table?

[Jeff Bullard]

Thanks for the reply.  I wrote a short C program using libpng to accomplish the task.  The projection information was lost but that's OK since all my images are EPSG 4326 (lat/long WGS84) as required for Google Earth KML.  Extent information was preserved in the final png image which was a surprise.

Too bad KML doesn't support this because it would allow the user to change the color table on-the-fly to get better contrast in some weather features.






________________________________
From: Chris 'Xenon' Hanson <xenon at 3dnature.com>
To: Jeff Bullard <jeffbullard2000 at yahoo.com>; "Geotiff at lists.maptools.org >> GeoTIFF Mailing List" <geotiff at lists.maptools.org>
Sent: Sunday, February 15, 2009 12:04:49 PM
Subject: Re: [Geotiff] Geotiff List: Tool to convert 8-bit gray to RGBA using a custom color table?

Jeff Bullard wrote:
> GeoTIFF list,
> I have weather data that is represented as an 8-bit GeoTIFF with one
> band (grayscale).  I would like to use a color table to convert into
> RGBA for map display.
> Are there any existing tools to do this?  I use a linux platform with
> FWTools for most of my work.
> Previously I used Mapserver and a mapfile to render single-band raster
> into a color map.  Now I'm trying Google Earth API to display the same
> maps.  I'm new at KML and have found no way to use KML to do simple
> color mapping that my current mapfiles perform, which is to render the
> grayscale into 6 shades of blue.  I'm hoping to use some GDAL utility to
> convert the grayscale GeoTIFFs into RGBA using a color table stored in a
> file.  I haven't found a way to do it.
> My other alternative is to write some code in C using libtiff and/or
> libpng to perform the color operations.  Before I get into that I want
> to ask the list f there is a simple way to do it using existing tools.  

  I don't think KML can do it. You might be able to do it with a combination of netpbm
(which I think can colorize a greyscale) and fwtools (to capture the metadata before
netpbm and reinsert it afterward).

> Thanks,
> Jeff Bullard


-- 
     Chris 'Xenon' Hanson | Xenon @ 3D Nature | http://www.3DNature.com/
"I set the wheels in motion, turn up all the machines, activate the programs,
  and run behind the scenes. I set the clouds in motion, turn up light and sound,
  activate the window, and watch the world go 'round." -Prime Mover, Rush.



      
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