Simple BASH script to merge pictures into a single picture, transparently overlayed

merge.sh

#/usr/bin/env bash

# expecting a list of files "trans_vlcsnap-000??.png" that I want to merge into
# file with all images transparently overlayed
# 
# need to create transparent images first, but the transparency has to be exponential
# otherwise the single images will blend out too fast in the merged result

for i in $(seq 23 59); do
 prev=$(( $i-1 ))
 # create transparent file here
 composite -compose over -alpha On trans_vlcsnap-000${i}.png out.png out-${i}.png
  cp out-${i}.png out.png
done