On samedi 11 février 2017 18:18:35 CET Stephen Woodbridge wrote: > Hi All, > > I need your wisdom. I'm downloading NAIP DOQQs in GTiff format and I > have a processing chain something like the following: > > gdalwarp -t_srs EPSG:4326 -dstalpha -r "bilinear -multi -co TILED=YES > -dstnodata '0 0 0' srctiff tmpfile > > nearblack -nb 15 -q tmpfile > > gdal_translate -co TILED=YES -co JPEG_QUALITY=90 -co COMPRESS=JPEG -co > PHOTOMETRIC=YCBCR -b 1 -b 2 -b 3 -mask auto --config > GDAL_TIFF_INTERNAL_MASK YES tmpfile, target > > nearblack -nb 5 -q target > > gdaladdo -clean -r bilinear target 2 4 8 16 32 64 128 512 > > And create a tileindex for mapserver of all the tiffs > > If I skip the gdal_translate (ie: JPEG compression) and the 2nd > nearblack, the doqq tiles are perfect with no nearblack edges between > the doqq tiles. But when a JPEG compress them, I get edges between the > doqqs like this: > > http://imaptools.com:8080/dl/doqq-issue.jpg > > I've never used the JPEG in tiff compression and I'm very impressed by > the amount of size reduction there and how good the image remains, but I > have not been able to figure out the magic trick to clearing the edge > artifacts.
Steve, I managed to replicate something similar to the above with an image I've at hand. The cause of the issue is the nearblack invokation after the gdal_translate. The effect of this nearblack is to "eat" some pixels at the border of the validity / invalidity transition, but that doesn't update the existing mask. If you add -setmask to this nearblack, that should fix it. Even better, I think you can just remove this second nearblack. And you probably must add -setalpha for the first nearblack invokation as well. Even -- Spatialys - Geospatial professional services http://www.spatialys.com
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