What format do you want the alphas channel in after running gdal_polygonize.py? I ask because after processing you could open the input and read just the alpha band (band 4 I assume). Here is a short script framework that might get you started.
Something like: from osgeo import gdal gdal.open(inpudataset, gdal.GA_ReadOnly) #Create an output driverFormat = "GTiff" #Any GDAL supported write format driver = gdal.GetDriverByName(driverFormat) outdataset = driver.Create(options.output, dataset.RasterXSize, dataset.RasterYSize, dataset.RasterCount) outdataset.SetProjection(dataset.GetProjection()) outdataset.SetGeoTransform(dataset.GetGeoTransform()) inband = gdal.GetRasterBand(4) #Band counts are 1 based. I am assuming that your band 4 is alpha. #Read in the gdal array input_band = inband.ReadAsArray() outdataset.GetRasterBand(1).WriteArray(input_band, 0, 0) Someone with more experience might be able to tell you a method that uses CreateCopy(), but I think that it isn't possible to selectively copy bands. Hope that that helps, Jay On Mon, Jul 25, 2011 at 8:19 PM, jt2000 <thak...@nexgenwireless.com> wrote: > I have a very large raster file with data in the alpha band. I need to > vectorize it and associate band 4 data with resulting polygons. > > Is there anyway to preserve alpha channel data or get that data associated > with vectorized file after using gdal_polygonize.py? > > -- > View this message in context: > http://osgeo-org.1803224.n2.nabble.com/preserving-alpha-channel-data-with-gdal-transform-py-tp6620877p6620877.html > Sent from the GDAL - Dev mailing list archive at Nabble.com. > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/gdal-dev >
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