[mapserver-users] a question about tiffimages

[kenboss]

We use an combination of ERDAS, Image Alchemy, and the geotif libraries for our 
raster image preprocessing.  Alchemy does a nice job of implementing the 
Heckbert median cut algorithm for color quantization.  It provides some 
fine-tuning options, including palette sorting by popularity, which is handy in 
a mapserver context in that you can use it to ensure that only the 
least-frequently used colors get swapped out for some approximation when the 
palette becomes over-allocated.  The downside to Alchemy is that it's 
proprietary (about $500 per *nix license).  I'm sure that public domain packages 
like Image Magick and the Gimp should be able to meet these needs as well, but 
haven't tried them since we've already got a working solution.  

Would it be nice if GDAL could handle all of our image preprocessing needs?  
Sure, especially since GDAL is spatially aware, so there would presumably be 
less need to muck around with map projection information than there is when 
working with spatially-unaware image processing packages.  On the other hand, 
there are already public domain packages that can be employed for these 
purposes, so I'm not sure how high on the GDAL development priority list these 
things would need to go.

--Ken

=============================================================================
Ken Boss                                
Digital Image Analysis / Web Stuff       Forestry Resource Assessment
kenboss at dilbert.dnr.state.mn.us          Minnesota Dept. of Natural Resources
Voice: 218 327 4449 ext. 237             413 SE 13th Street                 
Fax:   218 327 4517                      Grand Rapids, MN  55744          USA
                   www.ra.dnr.state.mn.us
=============================================================================



> There are algorithms in GDAL for colour quantization but they aren't directly
> used by MapServer.  It seems to me that this sort of thing should be
> done as a preprocessing stage before putting up data for use with MapServer.
> Right?  What do people use for preprocessing their raster images into 
> paletted form?  Is there interest in my providing some preparation tools 
> for applying image enhancements, and doing colour quantization with 
> detailed control?  I have these in rough form already as part of GDAL.
> 
> Best regards,
> 
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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