I have a raster of roads saved from a WMS, this a multiband raster. Its red(main) an grey(back) roads.

When using the raster calculator I can select most of the red road by using: Band@1 > 200

But what expression is to be used to select the grey road?

At all grey colours, the 3 bands have the same value. My guess was that this would work, but it did not: Band@1 = Band@2 = Band@3.

I have tried a couple of other variants, but no success.


Using a sample of RGB raster of 4 cells:

  • Upper left cell: Light grey (150, 150, 150)
  • Lower left cell: Dark grey (100, 100, 100)
  • Upper right cell: Red (250, 0, 0)
  • Lower right cell: Blue (0, 0, 250)

enter image description here

Equation to the Raster calculator to create the filter:

( "Band@1" - "Band@2" = 0) * ( "Band@2" - "Band@3" = 0 ) = 1

(This also works without = 1 .)

The filter returns 1 for R,G,B band (or @1, @2, @3 as in Raster calculator) have the same value.

enter image description here

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