I am currently analyzing some coral reef data. I have PNG files that I have inserted into ArcGIS Pro that look like this zoomed in. The red represents actual coral material while the black is substrate.

Zoomed in PNG file of coral

I have used raster to polygon to create a polygon feature of this coral that turns out like this:

Zoomed in Polygon layer of coral

Instead of creating a polygon layer that has orange polygons that represent only coral material, the raster to polygon tool instead fills in the space inside of coral material polygons that is supposed to be substrate to also be representative of coral material. This is incorrect.

Is there anyway that I can either:

  1. convert the raster to a polygon without filling in these spaces; or
  2. be able to delete these polygons within the actual coral material polygons using a tool or selection feature all though they are the same layer.

I have previously just used editor mode to go through and delete them by hand, by this takes several days as there are so many.


I'm guessing the issue is with the fact that the PNG file is a 4 band raster, so which band is the conversion tool using? What you see as black holes within red may actually be ever so slightly different to the exterior black colouring.

If this was me I would:

  1. Run Make raster Layer tool extracting band 1
  2. Identify the value for your red areas in your extracted layer
  3. Run Extract by attributes tool extract where VALUE = xxx (value identified in step 2)
  4. Run raster to polygon tool.

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