[gdal-dev] trying to change regionator image resampling to
warmerdam at pobox.com
Thu Nov 12 15:17:19 EST 2009
Mary Jo Brodzik wrote:
> Dear gdal-dev list members,
> I'm using a python tool called the regionator
> (http://code.google.com/p/regionator/wiki/ Welcome) on a large
> (14352x7440) png image. The regionator uses the GDAL library to
> resample subsets of the original image into much smaller chunk images.
> These images are set up at increasing levels of detail in a kml file
> that make the download of this information into a googleEarth client
> much more efficient.
> The png is color and includes transparency; its approximate resolution
> is 500 meters. I basically have 4 colors in the original image, black,
> white, blue and yellow. The output images that regionator is producing
> are great, but when I zoom in to distances where the original pixel
> sizes are visible, it looks like the resampling did some averaging
> across the 4 colors, so I'm getting blue sections surrounded by a blue
> halo that bleeds into white, and yellow and blue values bleeding into
> each other, etc.
> I'd like to control the resampling, and force it to do nearest-neighbor
> rather than averaging to eliminate the halos. It looks to me like the
> regionator is doing the resampling with calls to ReadRaster and
> WriteRaster in in a class called extractor.py, but I don't know enough
> about the GDAL libraries to know how to change them. Is it possible to
> force the resampling to be nearest neighbor? extractor.py isn't
> terribly large or complicated, so I'm including it here (below).
ReadRaster() cannot itself be modified to do bilinear resampling.
I would suggest you try out gdal2tiles.py which does something similar
to regionator but with many more options.
You might also find MapTiler of interest:
I set the clouds in motion - turn up | Frank Warmerdam, warmerdam at pobox.com
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