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I'd like to downsample a DEM raster from 2m per pixel to 8m. I've tried using SAGA Multilevel B-spline interpolation (from raster) as suggested here, but though that results in an 8m resolution it also does some pretty drastic smoothing/blurring somewhat similar to a Gaussian filter.

I just want a simple downsample, ie take a 4 by 4 square of pixels and replace it with one pixel with their average value.

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Export/Save the image. In the export dialog window (Save Raster layer as...), you can define the new resolution. Be sure to select Raw data as output mode (if you don't want a rendered image for visualization purpose only as this modyfies data like bit depth):

enter image description here

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  • I tried this and found that, as well as increasing the pixel size from 2 to 8 metres as expected, it also halved the bit depth from 16 Bit to 8 Bit. I can't work out why sample rate and bit depth would affect one another?
    – flyhigher
    Commented Oct 14, 2023 at 17:11
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    Could you provide a small sample as test data? Save as... should not change the data type. Is it right that the original DEM has Int16 as data type?
    – user30184
    Commented Oct 14, 2023 at 18:36
  • The original DEM was 32 Bit. The DEM is for use in Blender, and needs to be in UInt 16 Bit, so I used Translate to reformat. I've also used the Raster Calculator to normalise the max values to 65535 (2^16), again for the best results in Blender. Export >Save As Rendered image then reduces the bit depth to 8 Bits. Saving as Data doesn't change the bit depth. Perhaps there's an obvious reason for this? Anyway, looks like saving as Data is the way to go.
    – flyhigher
    Commented Oct 14, 2023 at 19:52

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