[Geoserver-users] Rendering quality of COG files

Hello,

I have several COG files stored on S3 compatible storage. I use a mosaic to access them in GeoServer (no access problem).

When I use WMS to view the assembled output I find the result (left) not as good as the original file (right).
image (5).png

I use GeoServer 2.25.0.

Is it related to the configuration of my GS instance or to the input files (an example of the file is attached)?

PLANIGN11_0440_6950_L93.tif (857 KB)

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Alexandre Gacon

What do you have your resample method set to? I’ve found nearest neighbour gives better results that average on maps like that

Ian

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Alexandre Gacon
Ian Turton

Hello Ian,

I use the default interpolation method, which is the nearest neighbour one.

Alexandre

image (5).jpg

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Alexandre Gacon
Ian Turton

Alexandre Gacon

Hi Alexandre,
I would suggest trying out different interpolation methods on the one hand (for smoother display of labels bilinear or bicubic could work) and other output formats on the other hand (e.g. full PNG for fewer artifacts).
I also use COG quite a lot, since I mostly use JPEG or PNG8 for output, I accept a slightly degraded quality.
Cheers, Niko

image (5).jpg

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Alexandre Gacon
Ian Turton

Alexandre Gacon

Hi Alexandre,
I have the impression overviews might not be used there… things to check:

  • Do the COG have overviews? If so, maybe check the algorithm you used to compute them (I typically use bilinear)
  • Is the mosaic possibly configured so that the COG overviews are not used, because it was created with a sample file that did not have any? You’d see it because the mosaic property files has levelsnum=1 (if that is coupled with heterogeneous=false, or lack of the heterogeneous property, the mosaic will likely assume there is only the base level)

image (5).jpg

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Regards,

Andrea Aime

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Alexandre Gacon
Ian Turton

Alexandre Gacon