Even Rouault wrote: > > Selon Jukka Rahkonen <[email protected]>: > > > Hi, > > > > I thought this would be easy but it was not. > > > > I have a mosaic of images which do not fill the whole > bounding box of the > > area. > > I made a .VRT file the images and converted the virtual > raster into geotiff. > > Now > > I have a nice mosaic but it has black boxes in the areas > where I do not have > > source data. An example of the result is here > > http://latuviitta.org/documents/nodata_3.tif > > > > I would rather paint nodata areas with white instead of > black. But how can I > > make it? I thought that gdalwarp -dstnodata would do it but > areas of missing > > source data remains black > > gdalwarp -dstnodata "255,255,255" nodata.vrt nodata_3.tif > > > > The following command does make the black box white but > unfortunately is is > > also > > changing everything that was black in the orininal images, > including all the > > texts, into white: > > gdalwarp -dstnodata "255,255,255" -srcnodata "0,0,0" > nodata.vrt nodata_3.tif > > > > So what is the correct way to do this simple task? > > Jukka, > > Several options : > > - use the -addalpha option of gdalbuildvrt
Doing gdalbuildvrt -addalpha nodata_alpha.vrt *.tif and then gdalwarp -dstnodata "255,255,255" nodata_alpha.vrt white_nodata.tif makes the desired result. > - use nearblack -setalpha ( http://gdal.org/nearblack.html ) ? Did not try this one. > - cheat a bit and create a white image that you add as the > first position in > your VRT. > > This can be a single pixel image that you artifically expand > to full VRT size, > like this : > > <SrcRect xOff="0" yOff="0" xSize="1" ySize="1"/> > <DstRect xOff="0" yOff="0" xSize="replace_by_vrt_x_size" > ySize="replace_by_vrt_y_size"/> I have nothing against cheating and I will try this with my real dataset. Dataset is pretty big and running it through gdalwarp takes several hours more time than running it through gdal_translate. > Best regards, Thank you once again. -Jukka- > > Even > _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
