Edge interpolation or something

[gagecarto]

I have a raster dataset with values 0-255. In this dataset, 0 is no data. Rendering tiles at some zoom levels results in weird values along the edge of data/no data.

See below where white is no data and green is mid range values. There are red cells at zoom 7 in this example

When I zoom to zomething greater like z10, those edge effects between data/no data disappear

I tile call to produce one of these looks something like this.
https://titiler.xyz/cog/tiles/WebMercatorQuad/7/23/45@1x?url=urlToMyDatasetbidx=1&maxzoom=8&nodata=0&rescale=1,255&colormap_name=rdylgn

I was thinking changing it to a different interpolation like MIN would fix the issue but I am not allowed to use that method for some reason.

[vincentsarago]

My guess is that the artefact comes from the overviews creations. do you know what resampling you used when the COG was created @gagecarto

[gagecarto]

Bingo!

Overviews were resampled with bilinear.. I'll try nearest and see if that clears things up.

Thanks @vincentsarago

[mradamcox]

@gagecarto I'm seeing some similar artifacts in my own images, which are JPEG-compressed COGs. Did you find a resampling algorithm that doesn't cause this?

[gagecarto]

@mradamcox - switching to nearest fixed it for me