Remove noise surrounded by transparency

[jiexi]

I'm trying to remove the noise that runs around the border on these polaroid images






I think the correct approach is to separate out each part of the image that is completely surrounded by only transparent background, then discard the small pieces which should leave us with just the larger image?

[fmw42]

There are two ways to approach it. First is to use -morphology open on the alpha channel. The second is to use -connected-components to remove small regions.

These both work on your first image for me with IM 6.9.10.11 Q16 Mac OSX Sierra. But you will likely have to change the value for octagon:X or area-threshold=X

Code: Select all

convert wrnTV0w.png -channel a -morphology open octagon:5 +channel result.png

Code: Select all

convert wrnTV0w.png \
\( +clone -alpha extract -type bilevel \
-define connected-components:area-threshold=1000 \
-define connected-components:mean-color=true \
-connected-components 4 \) \
-alpha off -compose copy_opacity -composite \
result2.png

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