Selection to transparent - unexpected results

[SevenLime]

Hi guys,

I see this happen sometimes but never bothered to ask before now. Check out the two screenshots I took while editing an image of a phone. Notice the result after I clear a selection made with either fuzzy select or color select. 

Fuzzy select (2nd image):
1) Why is the content around the inside edge of the selection still partially visible?
2) Why is the content around the outside edge of the selection partially cleared? That area is outside the  selection so I imagine it shouldn't be changed. Maybe I have some fade setting enabled?


Color select (3rd image):
1) Why is there a translucent trail creeping up the edge of the phone? That trail was not shown as part of the color selection (zoom in to see the selection ants). If I turn the threshold way down then try to select and delete, that trail does not form.
 

Thanks a bunch from a new user. Happy to be here

[Ofnuts]

Things aren't always what they seem. On edges, the color of the pixels is a blend of the two colors on the two sides. Fuzzy select and color select select them totally or totally ignore them depending on threshold. So select+delete will either leave a faint rim (low threshold) or create a jagged edge (high threshold) or both (and there is no good threshold...).  

In addition, the ants show where the 50% mark of the selection is, so if the selection is fuzzy, it sits in the middle of the fuzz area, and there are partially selected pixels outside of the ants line. If you delete the selected pixels these partially selected pixels become partially transparent.

In fact with the sharp edges in your pictures you are facing about the same problems as people removing background around logos. See here form some hints.

[rich2005]

Just throwing a few thoughts in.

1. Using the fuzzy select tool. As mentioned by Ofnuts, if feather edges is enabled, do not be surprised with that semi-transparent border. Not easy to see from your screenshot but it is on. Turn it off. What to look for. https://imgur.com/gxn6Pea.jpg

2. Using the colour select tool. It would be very surprising if there were not varying amounts (depending on threshold value) of the selected colour scattered around: https://imgur.com/1VvTvu5.jpg

You can mitigate that by making an initial slightly oversize rectangular selection (with rounded corners & in replace mode) https://imgur.com/H1PnSJ9.jpg Then using the colour select tool in Intersection mode. https://imgur.com/kvacocR.jpg

A better way, if this is for a 'mock-up' image. Use a layer mask for ease of correction and maybe start off with a path to define the area.