"Leaky" boundary in mask made by brush selection tool

[henders64]

Hello Affinity Users Group -

I am using Affinity Photo to make a panorama of a mountain scene.  I used the brush selection tool to select the sky, at the end of which I used the "Refine" option to improve the details of the boundary between mountain and sky.  When I was finished, the boundary between mountain and sky, as delineated by the "marching ants," looked quite good, and at that point I made a mask based on that selection.  I was expecting the marching-ant boundary to be perfectly binary, with pure black on one side and pure white on the other.  However, when I take a close look at the white-black boundary of the mask, it is not very clean.  That is, the white part of the mask near the boundary has a number of gray pixels (within a width of 20-50 pixels or so), and the same is true for the black part of the mask near the boundary.  The result is that the mask near the boundary is "leaky."  One way to clean this up is to use the brush tool to clean up this "noise," painting white on one side and black on the other.  However, my panorama is large, and the white-black boundary has a lot of structure, so a manual repair using the brush tool would be quite tedious and time consuming.  Can anyone shed some light as to why I get this leaky boundary, and can you recommend an efficient way of cleaning it up?

Thank you.

[BarKeegan]

Have you tried using Channels to make selections, can be useful for things with uneven edges like hair, fur etc.

[Lee D]

It can depend on the image the selection is being made on. When you made the initial selection was Snap to edges enabled, this should help with a clear defined edge to select. Also how about Soft edges, was this enabled on the Context Toolbar as this would antialias the selection's edge. Meaning some pixels will be semi transparent, giving an appearance that is less sharp but often the preferred method.

[henders64]

Thanks to both of you.  My problem has evolved a little bit.

Yes, I had Snap to edges enabled.  Soft edges was not enabled.  Overall the edge is smooth.

I mostly solved the original problem in the Refine mode by doing Foreground and Background painting.  I would first click on "Black & White," and what I could see is that there was a lot of gray near the boundary that was causing the leakage.  Then I would choose background and paint black near the boundary, and when I release, it would fill in a lot of the leaky gray.  Ditto for the white.  I would choose foreground and paint over the gray pixels near the boundary, and when I release the mouse, it would fill in a lot of the gray.

The bigger problem I'm having right now is a blue halo at the boundary between sky and mountain.  The sky behind the mountains is bright blue.  When I select the sky using the brush tool, then add a new sky that's masked to the sky selection, I can see a blue halo between the mountains and the new sky.  That blue halo is the old sky that's peeking through.  I played with the different options in Refine (border width, ramp, smooth, etc.) but that blue halo won't go away.  In the end I was able to fix the problem using the Grow / Shrink feature applied to the sky selection.  If you have a better method I'm all ears.

Thanks.