[gdal-dev] ZSTD compression level 17 smaller than 18+?

[Matt.Wilkie at yukon.ca]

So this is curious: output to Cloud optimized Geotiff with ZSTD compression to Level 17 is smaller than levels 18-22. Or at least that's my results when testing compression results with Gdal 3.1 via Qgis 3.18 on Windows 10. I expected compression levels to get smaller with higher levels, at expense of longer and longer computation time. Levels 1 to 16 do that. Even more curious than 17 being the smallest of the lot is that each step 18 to 22 is progressively larger, albeit by a miniscule amount.

Here's my results:

% smaller than biggest  Bytes   Filename        Compression     Predictor       Level
24.2%   200,968,821     cog-zstd-pyes-lev17.tif zstd    yes     17
22.8%   204,567,155     cog-zstd-pyes-lev18.tif zstd    yes     18
22.8%   204,594,678
        cog-zstd-pyes-lev19.tif zstd    yes
        19
22.8%   204,594,678     cog-zstd-pyes-lev20.tif zstd    yes     20
22.8%   204,626,722     cog-zstd-pyes-lev21.tif zstd    yes     21
22.8%   204,635,985     cog-zstd-pyes-lev22.tif zstd    yes     22
22.6%   205,026,301     cog-zstd-pyes-lev16.tif zstd    yes     16
21.5%   208,039,012
        cog-zstd-pyes-lev15.tif zstd    yes     15
21.5%   208,094,559     cog-zstd-pyes-lev13.tif zstd    yes     13
21.5%   208,094,560     cog-zstd-pyes-lev14.tif zstd    yes     14
21.3%   208,714,731     cog-zstd-pyes-lev12.tif zstd    yes     12
21.2%   208,989,301     cog-zstd-pyes-lev11.tif zstd    yes     11
21.2%   208,989,994     cog-zstd-pyes-lev10.tif zstd    yes     10
21.1%   209,071,549     cog-zstd-pyes-lev9.tif  zstd    yes     9
21.0%   209,453,858     cog-zstd-pyes-lev8.tif  zstd    yes     8
20.9%   209,634,360     cog-zstd-pyes-lev7.tif  zstd    yes     7
20.7%   210,182,178     cog-zstd-pyes-lev6.tif  zstd    yes     6
20.4%   210,992,074     cog-zstd-pyes-lev5.tif  zstd    yes     5
18.9%   214,894,175     cog-zstd-pyes-lev4.tif  zstd    yes     4
17.4%   218,911,762     cog-zstd-pyes-lev3.tif  lzw     2       3
16.6%   220,991,236     cog-dflt-p2.tif deflate 2
13.0%   230,553,902     cog-zstd-pyes-lev2.tif  zstd    yes
        2
11.6%   234,277,147     cog-zstd-pyes-lev1.tif  zstd    yes     1
5.7%    249,979,858     cog-dflt-p1.tif deflate 1
0.0%    265,062,854     cog-lzw-p2.tif  lzw     2



Command line pattern:


gdal_translate ^

  -co compress=zstd ^

  -co predictor=yes ^

  -co level=3 ^

  -co num_threads=all_cpus ^

  -of cog ^

  mtn-view.tif ^

  mtn-view-cog-zstd-pyes-lev3.tif


Source image:


Name


AerialPhotos/AerialPhotos


URL


https://mapservices.gov.yk.ca/imagery/rest/services/AerialPhotos/AerialPhotos/ImageServer


Source


crs='EPSG:3578' format='JPGPNG' layer='' url='https://mapservices.gov.yk.ca/imagery/rest/services/AerialPhotos/AerialPhotos/ImageServer'


CRS


EPSG:3578 - NAD83 / Yukon Albers - Projected


Export extent


Upper Left, Lower Left, Upper Right, Lower Right

356750.816,  702590.026

356750.816,  699097.526

361572.583,  702590.026

361572.583,  699097.526


Pixel size


0.5m



Do others see the same thing?


?Cheers,

Matt Wilkie
Environment | Information Management & Technology | 867-667-8133 ?? Yukon.ca<http://yukon.ca/>
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