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

[Duarte Carreira]

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> 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> *Puolesta *Duarte
> Carreira
> *Lähetetty:* torstai 18. marraskuuta 2021 13.45
> *Vastaanottaja:* 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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