Is there any way I can reduce the colours of a TIFF to make conversion to polygon more efficient. There's quite a bit of artification on my original and I'd like to reduce it to 2 colours before the conversion (which I have done, however once re-saved it loses the referencing).

Reduced coluor image:

enter image description here

Original TIFF in QGIS

enter image description here

Output polygon with solid white removed

enter image description here

  • Write a VRT to preserve the metadata, or try Manifold which always treats tifs as geo, and has image edit tools. – mdsumner Aug 4 '16 at 10:29
  • try gdal_translate.exe -ot byte – klewis Aug 4 '16 at 12:47

In QGIS, you can use the raster calculator to reclass your raster in a binary way:


will set all cells with values greater 100 to 100, all other cells to 0.


I would try to reclass it into two classes using r.reclass in the GRASS toolbox, then do the standard raster-to-vector conversion.

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