Hi David,
following your indication, I started playing with the filter "frame_fuzzy".
Results are nice and very close to what I was expecting.
As with other filters, I started also trying to understand -step by step- the full logic of the filter (in order -maybe in a far future- to add some additional option).
Because I encountered a serious difficulty in understanding one piece of that code, I like to share with you my (very close to the ground...) question/opinion.
I post here the full code, highlighting the ununderstood lines of code:
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-v - -to_rgba -repeat @# -l[$>] nm=@{0,n}
-i[0] ($1;$2) -*[0] 2 ($5^$6^$7^$8) -r[-1] [-2] 100%,100%
-rectangle[-1] 0,0,100%,@{0,1},1,1
-rectangle[-1] 0,0,@{0,0},100%,1,1
-rm[0] -shift[-1] -$1,-$2,0,0,2 -spread[-1] $3 -b[-1] $4 -_fade 50,80
-nm $nm,1 -endl -done -v +
---------------------------------------------------------------------------------
as you see, my problem is on the
- creation of an image (as 0) having two rows and one colum and with a grey level corresponding to the two parameters in input $1 and $2
- multiplication of those two values by 2
- finally removing that image

my question is: what is the goal of this image?
it seems not to enter at all in the rest of the logic (as I said, I express here my very basic opinions)
using the console, I:
1-first executed the filter fully (got the expected result)
2-then I removed the "highlighted" lines of code (got the same result)

When you will have 2 minutes, could you verify my doubts?
Thanks a lot!!!

Hello dinasset.
Actually, this command '-frame_fuzzy' is one of the oldest command written, at a time where G'MIC had no mathematical expression evaluator.
This image [0] was then used to perform some arithmetic operations on the input arguments.
This is not needed anymore. A more 'modern' (and shorter) version of this command would be instead :

thanks a lot, David!