[gdal-dev] setting MAX_Z_ERROR on overviews compressed with LERC_DEFLATE

[Rahkonen Jukka (MML)]

Hi,

I have no experience on 32 bit images but play with gdaladdo and compression options and report what you find. External overviews (-ro) are handy for testing because you can simply rename or delete the .ovr file and make new run with other options. External overviews take some more space than it takes to add internal overviews into TIFF but best option as external should be best as internal too.

-Jukka Rahkonen-

Lähettäjä: Duarte Carreira <dncarreira at gmail.com>
Lähetetty: torstai 18. marraskuuta 2021 18.30
Vastaanottaja: Rahkonen Jukka (MML) <jukka.rahkonen at maanmittauslaitos.fi>
Kopio: gdal-dev at lists.osgeo.org
Aihe: Re: [gdal-dev] setting MAX_Z_ERROR on overviews compressed with LERC_DEFLATE

Well, it didn't even occur to me to compress the overviews with translate...
I was expecting a bit more compressing from lerc...

About tif 32bit, what compression do you think would yield better ratios?

Thanks.

Rahkonen Jukka (MML) <jukka.rahkonen at maanmittauslaitos.fi<mailto:jukka.rahkonen at maanmittauslaitos.fi>> escreveu no dia quinta, 18/11/2021 à(s) 12:41:
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-bounces at lists.osgeo.org<mailto:gdal-dev-bounces at lists.osgeo.org>> Puolesta Duarte Carreira
Lähetetty: torstai 18. marraskuuta 2021 13.45
Vastaanottaja: gdal-dev at lists.osgeo.org<mailto:gdal-dev at 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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