Overzooming with upsampling

[Plantain]

Problem description

Zooming past the maximum level of a COG should upsample using the specified resampling= algorithm, instead it seems to do a simple scale without any upsampling occurring.

Requesting tiles with:
https://localhost:8080/tiles/9/473/293@2x?resampling=lanczos

Zoom level 8 (native resolution for this COG)

Zoom level 9 (max zoom +1)

Notice the overzoomed image has large blocks - no upsampling is happening.

I'm not sure if this is a bug/feature request for titiler, or a limitation of rasterio?

Original file is at http://static2.skysight.io/demo.tiff

[Plantain]

zoomed in further to make it more obvious...

[vincentsarago]

@Plantain I'm sorry but I'm not seeing anything wrong here. I'll translate this issue as discussion because this is not really a bug (or if there is one it would be either on rio-tiler or rasterio)

Here is what I get for tile 9/473/293 with 1024x1024 tile size

[Plantain]

Ok - but I you set resampling=bilinear, I would not expect to see these 'pixel' blocks if it was upsampled with bilinear.

[vincentsarago]

here is what I get with bilinear

It's not clear to me what the correct result for you would be. Ideally it would help if you could produce the expected result so we can compare.

[Plantain]

Interesting, I'm not sure why I am not getting that when I add &resampling=bilinear, I get the same blocky image - possibly a terrible bug in my code, let me dig further.

I do still see 'pixel' blocks in your example though, my expectation was that with bilinear or basically any interpolation other than nearest, that there would never be blocky rendering

[lenalebt]

Hey, were you able to solve this @Plantain ? I am facing the same thing 😄 .

[lenalebt]

Ah, you know how this goes: The minute you ask someone, you find a solution. I was reprojecting as well, and did not really notice. When I started using reproject=bilinear instead of resampling=bilinear, it worked.