raster image preprocessing problem.

[Travis Kirstine GIS Tech]

Zhonghai,
My guess is that both the gdal_warp and gdal_merge utilities use the pusedo
colour table of the first image and apply that table to all other images, I
would try converting the gif to RGB geotiffs using the pct2rgb gdal utility
then go through your processing steps(warping and merging) then convert the
images back to 8bit GIFs.  I hope this helps

Travis
  -----Original Message-----
  From: UMN MapServer Users List [mailto:MAPSERVER-USERS at LISTS.UMN.EDU]On
Behalf Of Zhonghai Wang
  Sent: Tuesday, June 06, 2006 6:35 AM
  To: MAPSERVER-USERS at LISTS.UMN.EDU
  Subject: [UMN_MAPSERVER-USERS] raster image preprocessing problem.


  Hi there,

  I have a couple of GIFs with wld files, but the original Projection is not
the one I want, I tried to use the Proj4 to reproject them on-the-fly, but
it takes really long to perform the map request, therefore I tried to
preprocess the images with GDAL tools, but I've got some problems here:

  1. problem with gdalwarp: trying to mosaic the images into one output
file, but only the first image has the correct image color, the other images
are rendered with strange colors, is this a common problem if using gdalwarp
to mosaic images?

  2.problem with gdal_merge.py: after trying the gdalwarp command, I've
tried the gdal_merge.py command to merge all the images together with
the -pct parameter, unfortunately, the merged image is the same as the first
try. is it possible to merge images using the command with the correct color
table?

  BTW: I can not use the gdal_translate command, since there are gaps
between the reprojected images.

  thanks for your info.

  zhonghai
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/mapserver-users/attachments/20060606/38bb24e0/attachment.html