Here is another solution, could you tranlate this. I have tryed, with no luck.
convert Sir_amik_varze_detail.PNG \
\( -clone 0 -alpha off \) \
\( -clone 0 -alpha extract -blur 1x65000 -level 50x100% \) \
-delete 0 -compose copy_opacity -composite Sir_amik_varze_detail1.png
convert Sir_amik_varze_detail.PNG -channel A -blur 1x65000 -level 50x100% \
-channel rgba Sir_amik_varze_detail1b.png