Select features from a raster based on their colour to create a new layer

Question

I have a map of the UK imported as a raster. It was originally a JPEG and has areas that are coloured red and purple. I have a data set imported from a CSV file showing UK locations as dots. I want to select the dots that are within the coloured areas of the raster map.

I thought that in order to do this, I would need to create a new layer only containing the parts of the map that are red and purple and then use this to clip the other layer. I don't know how to just select these areas of the map without just doing it visually using a polygon (this would take ages, as there is so much detail!). Is there a way to select features by their colour?

Senshi · Answer

In QGIS, try the Add raster values to points tool from the SAGA toolbox (included in the default distribution of QGIS).

That way, you can add the RGB values to your point features as attributes, and then use all the regular feature filtering on those values.

Select features from a raster based on their colour to create a new layer

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