Hi, I made a couple of simple tests by following https://trac.osgeo.org/gdal/wiki/CloudOptimizedGeoTIFF, here are the results:
Create a jpeg compressed GeoTIFF and couple of overviews gdal_translate -of GTiff -co tiled=yes -co compress=jpeg p4433h.tif p2-jpeg.tif gdaladdo --config COMPRESS_OVERVIEW JPEG p2-jpeg.tif 2 4 Test how the main image and overviews behave gdal_translate -co tiled=yes -co COPY_SRC_OVERVIEWS=YES p2-jpeg.tif cog21.tif gdal_translate -co tiled=yes -co compress=jpeg -co COPY_SRC_OVERVIEWS=YES p2-jpeg.tif cog22.tif Check file sizes: 575 913 074 cog21.tif 131 203 903 cog22.tif Both images have 2 overviews and obviously the full resolution data are not copied. I believe that it means that the jpeg compressed tiles are uncompressed and processed again that leads into quality loss just as you feared. What I do not understand is what gdalcompare reports. gdalcompare p2-jpeg.tif cog21.tif Files differ at the binary level. Differences Found: 1 This is understandable, the main tiles are jpeg compresses vs. uncompressed so they are not the same. However, pixels are the same because jpeg is converted into uncompressed with no loss. But then, this is the beginning of the report about original and jpeg-compressed with overviews copied. gdalcompare p2-jpeg.tif cog28.tif Files differ at the binary level. Band 1 checksum difference: Golden: 30664 New: 57443 Pixels Differing: 62249009 Maximum Pixel Difference: 13.0 Band 1 overview 0 checksum difference: Golden: 19959 New: 54816 Pixels Differing: 28090066 Maximum Pixel Difference: 39.0 Band 1 overview 1 checksum difference: Golden: 5318 New: 34525 Pixels Differing: 8059334 Maximum Pixel Difference: 75.0 ... more bands ... So not only the full resolution images differ but also the overviews even they should be just copied. I got similar results also when I used "cog" as outputformat, and with GDAL versions 3.14 and 3.3.0. The cog driver creates two overviews just as documented (the AUTO overview option) but gdalcompare reports pretty large differences in pixel values. Maybe you could just try to use your existing jpeg-in-geotiff images in cloud. They may behave rather well even the reading application must read a little bit more bytes from that GeoTIFF structure. -Jukka Rahkonen- mhw-at-yg wrote > Hi Folks, > > I have a lot of jpeg-in-geotiff imagery that I would like to convert to > Cloud Optimized Geotiff. Is there any way to do that without re-encoding > the > pixel values? > > I'm trying to avoid paying the price of: > > * lossy + lossy compression that results from feeding a jpeg source to > a > jpeg output file, and > * lossy + lossless that comes from feeding a jpeg source to lossless > output file, which means x4+ storage requirements > > -Matt > > (x-posted to GIS Stack Exchange, > https://gis.stackexchange.com/questions/387632) > > > > ----- > -Matt > -- > Sent from: http://osgeo-org.1560.x6.nabble.com/GDAL-Dev-f3742093.html > _______________________________________________ > gdal-dev mailing list > gdal-dev@.osgeo > https://lists.osgeo.org/mailman/listinfo/gdal-dev -- Sent from: http://osgeo-org.1560.x6.nabble.com/GDAL-Dev-f3742093.html _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/gdal-dev
