Jacob Adams wrote > I'd like to check my understanding of the impact of the tile size on > JPEG-compressed geotiffs. > > I've been getting dark bands 4 or 5 pixels wide on the bottom and right > edges of the image when manually creating large image tiles from a > collection of smaller tiles. I'm using the common aggressive compression > settings for jpeg with a specified extent (in map units) as follows: > gdal_merge.py -ps .25 .25 -ul_lr 1528148 3773703 1529109 3772785 -co > compress=jpeg -co interleave=pixel -co photometric=ycbcr -co tiled=yes -o > <outfile> > > <infiles> > While subtle, they are distracting and are more visible when placed next > to other imagery or when resampling. > > I've found two ways to get rid of them via trial and error: > 1) Don't use tiling. > 2) Make sure your image size (in pixels) is a multiple of your tile size. > > I want to use tiling to speed up access time. If I adjust the extent to > make the image size a multiple of some of the factors of the tile size, > such as 128, 16, or 8 (for a default tile size of 256x256) the dark area > is still there but shrinks to one or two pixels. This tells me it's not > related to the MCU of the JPEG compression. > > Am I correct in saying that the image size should be a multiple of the > tile size when using compress=jpeg and tiled=yes to avoid generating these > darker bands on the bottom and right edges of the images? > > Thanks, > Jake Adams > > _______________________________________________ > gdal-dev mailing list
> [email protected] > https://lists.osgeo.org/mailman/listinfo/gdal-dev Hi, I would also have a try by making first a virtual mosaic with gdalbuildvrt and then running gdal_translate instead of using gdal_merge.py. -Jukka Rahkonen- -- Sent from: http://osgeo-org.1560.x6.nabble.com/GDAL-Dev-f3742093.html _______________________________________________ gdal-dev mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/gdal-dev
