Le jeudi 16 octobre 2014 10:15:53, M Lewis a écrit : > Thanks Even > > I am assuming that even in doing this there may still be an issue with > differentiating between pixels of pure black and this 0 'no-data' value in > an 8 bit band where raster min gives 0 and raster max gives 255.....ah > well. > > There is another question and I have noticed that the dataset created from > AutoCreateWarpedVRT has different raster min and max values. > > One of the rasters (a single UInt16 band, rotated) has a raster min of > 337.0 and a raster max of 872.0 when computed using ComputeRasterMinMax(). > > However the AutoCreateWarpedVRT dataset created from this original dataset > has a min of 0.0 and a max of 772.0, why?????
The 0's probably come from the black collar ( ComputeRasterMinMax() cannot make the difference between valid pixels and the black collar, unless you define 0 as nodata) And the different max is probably due to the resampling done when warping that misses some pixels (if nearest neighbour) or "average" them. You could play with different resampling algorithms. > > My plan (using your idea) of setting the no-data value to 0.0 would work on > the original dataset as the minimum is > 0.0 and therefore 0.0 could be > filtered out; however due to the conversion by the AutoCreateWarpedVRT, 0.0 > is now a valid colour and once again falls into the issue of whether 0.0 is > 'no-data' or a genuine colour. > > Thanks > > Martin > > > > -- > View this message in context: > http://osgeo-org.1560.x6.nabble.com/Remove-Black-Areas-From-Rotated-Images > -tp5167665p5167762.html Sent from the GDAL - Dev mailing list archive at > Nabble.com. > _______________________________________________ > gdal-dev mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/gdal-dev -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
