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Hello:

  I've been trying to figure out how to blend the edges of a G'mic generated annular steiner chain with round tiles. I've tried feathering by creating a channel selection then inverting it- didn't work.  I then tried a gradient and that didn't work; blurs (gaussian, etc.) affect the whole image and I simply want to blur the edges of the round tiles (circles).

I'm using gimp 2.10 on win 8 64bit. 

Any guidance would be greatly appreciated.

Blend using a layer mask. All good practice for using layer mask and selections.

[attachment=5995]

Add a layer mask Layer -> Mask -> Add Layer Mask using the layers alpha for the mask
Work on the layer mask using Layer -> Mask -> Show Layer Mask
Create a selection around the annular ring of circles. I used a colour select initially and subtracted from that with a quick mask, however no reason why you could not paint directly in with a round brush.
Apply a gradient white-to-black in 'shaped (angular)' mode.
Kill the selection, toggle show layer mask off.
Tidy up by hand.

As a 4 minute video:  https://youtu.be/dWJ41hf_ntI