I believe many know the Droste effect ,
to refresh the memory below as example its first and most classic example from the author of the mathmap script Josh Sommers


In Mathmap there is a filter for this effect ( NOTE now there is a "droste" filter also in gmic that does look interesting but has a quite different effect...a effect more close to the reflections of a object placed between 2 mirrors , and far from the droste "spirals" of the examples ) BUT to work at best with this filters the images needs some previous edit


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It would be nice a script that take care of all the pre-edit and then call Mathmap droste in not-interactive mode (using some presets, i may prepare a fews ) and/or in interactive mode

There are 3 cases (ABC)

A )the Droste effect is used on a image that has in the center a transparent zone ... let say a zone that was selected and then erased

in this case the pre-edit consist in assure a very smooth transition on the edges of the transparent zone

So supposing the user already selected the central part to delete the filter should
1 feather the selection (usually 5px or more)
2 clear
3 invert the selection
4 enlarge of few pixel the selection,
5 apply a generous gaussian blur
6) select all (or none)
7) call mathmap or gmic

B ) Opposite , the image has a transparent zone in the periphery so the filter will be applied on external transparency

Exactly same routine then for A )

C) The filter will be applied to a image that doesn't contain any transparent zone.

1) select all
3) shrink selection of (at least 8px)
4) select rounded corners (round the selection corner
5) feather selection
6 ) clear
7) invert selection
8) enlarge selection of few px
9) blur
10) select all
11) call mathmap or gmic

I have clear how this will help to get cleaner results with the mathmap droste effect

I believe a similar routine could be useful also for the gmic version of Droste , but till now i didn't used much the gmic version


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PS maybe i may summarize with few words :
if there is a transparent area or a selection doesn't matter if in the center or in the periphery, the edit consist in make the transition at the edges the smoother possible
if not image corners must be rounded a tiny transparent zone should be created to the image periphery, and the transition should be made smooth as possible