Blur tool convolution and selections

If I correctly understand how the blur tool works, it averages the nearest nine pixels. However, when I create a selection, pixels outside the selection will still be accounted for in the blur average. This probably isn’t the expected behavior, since I’d like to blur only within the selection.

Bug observed on Aseprite v1.2.27-x64, and it should be relatively straightforward to reproduce

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This is how blur works in every drawing program I’ve used. It only changes what’s inside the selection, but will look at what is outside of the selection to produce the blur. If it did not, there would be visual discontinuities between the blurred area and the unblurred area.

However, sometimes these visual discontinuities are desirable, such as if you want to blur one discrete element without other elements getting in the way. This can currently be done by placing the objects to be blurred on their own layer, but it would be nice if the convolution menu had options for different ways to treat selection edges, including options to treat pixels outside the selection as a repetition of the pixels inside the edges (this might get complicated for non-rectangular selections) and to treat them as transparent (non-Background layers) or as the background colour (Background layers).

This is affecting me as well. If the logic looked at the closest 9 pixels but ignored any of them outside the selection, blend would work as I expect. This also pulls alpha outside the selection into the colored pixels which is definitely not desired either. Please fix this! Thanks!

“If the logic looked at the closest 9 pixels but ignored any of them outside the selection, blend would work as I expect.”
no, it wouldn’t. to work like that the effect would have to internally duplicate the edge pixels. there is a setting in after effects for blur called “repeat edge pixels” which does what you’re asking for. hovewer it should be noted that that’s an additional option, not default behaviour.
the standard is - as eishiya wrote - the current behaviour.

hence this is not a bug, you are asking for additional feature.

You’re right in that most other programs do it that way so I guess it’d be considered a feature, although I use that term loosely. When trying to blur near an edge, it isn’t intuitive to the user that it would pull color from something they haven’t selected - in fact, that’s inconsistent from how selection typically works.

Regardless, I would really love that feature! Thanks for the help.

i agree that it would be nice to have it