How to separate details by color from raster? Is it possible in ArcGIS or any other software? I have tried Spatial Analyst.

I want to use RGB .tiff image which is scanned map. It consists of all the details having different colors. I want to separate all details like roads, railway as they have different colors so that auto digitization by ArcScan tool will be easier.

  • 2
    Could you provide a visual example highlighting what you are after? Additionally, it would be helpful to describe what type of rasters you are working with (e.g. multiband satellite imagery, single band NDVI, etc...).
    – Aaron
    May 7, 2015 at 14:07
  • I want to use RGB .tiff image.which is scanned map. It consist of all the details having different colors. So I want to separate all details like roads,railway as they have different colors.so that auto digitization by arcscan tool will be easier. May 7, 2015 at 14:36
  • The main issue is your source is RGB, which means there are actually three values that make up any single value in the map. And that 'red' could actually be a range of values. There are several ways you could approach this problem. Merge the bands to one, use image software to convert to an indexed color table, extract/reclassify each color to its own raster as Mox suggests, methods I discuss here, etc.
    – Chris W
    May 7, 2015 at 22:32
  • Thank you Chris, link that you have provided have so many new ideas to improve my result and to do fast. I have used spatial analyst of ArcGIS. May 9, 2015 at 7:13

1 Answer 1


If you are only concerned with roads, you might sample a series of roads, then 'query' the raster such that only pixels with those colors are left. Doing the actual query would require doing something like reclassing the raster so that all non-road colored pixels become white.

  • Thank you. I will try with this idea. I think same can be appyed in other feature too. May 7, 2015 at 19:34
  • Thank you Mox, I got my desired result by classifying image then to extract it. May 9, 2015 at 7:06

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