Hi, I made some tests with an 8 bit RGB image. First observation was that gdaladdo supports lerc_deflate (even it is not documented), but it does not support “MAX_Z_ERROR”. This yields same sized ovr file with or without max_z_error. gdaladdo -ro lerc_def2.tif --config compress_overview lerc_deflate --config MAX_Z_ERROR 10
Another observation was that this option would really save some disk space. I compressed the lossless ovr file with gdal_translate by using -co max_z_error=10 and file sizes were: source tiff: 432 072 372 bytes lecr_deflate cog without overviews: 311 258 085 bytes lossless lerc_deflate overviews: 118 954 009 bytes lerc_deflare overviews with z_error=10: 52 400 583 bytes For comparison even not relevant to original question about 32 bit data jpeg-ycbcr overviews with default quality: 14 481 967 bytes -Jukka Rahkonen- Lähettäjä: gdal-dev <gdal-dev-boun...@lists.osgeo.org> Puolesta Duarte Carreira Lähetetty: torstai 18. marraskuuta 2021 13.45 Vastaanottaja: gdal-dev@lists.osgeo.org Aihe: [gdal-dev] setting MAX_Z_ERROR on overviews compressed with LERC_DEFLATE Hi there. I am looking into compressing overviews for a DEM, with LERC_DEFLATE and it works. But I'm trying to set the precision loss and get better compression, since for overviews I don't really care that much. Ok, so the question is how to set the MAX_Z_ERROR for overviews compressed with LERC_DEFLATE? More context: My reasoning is to compress losslessly the dem with deflate predictor 3, and then compress "lossly" the overviews with lerc_deflate. Since this is 32bit dataset, I can't use jpeg on the overviews. Thanks in advance. Duarte
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