liquid_input.sh

#!/bin/bash

# generates a liquid gif using an input image.
# usage: ./liquid_input.sh Replace inputimage with your input image. After a 
# while a liquid gif be created with your input image as its source. If you 
# use a gif as input the duration of the output gif will be taken from its 
# shortest input. The animated displacement map generated by ImageMagick 
# is 36 frames. If the input gif has 12 frames the output gif will be 12 
# frames but will be cut off and won't loop seamlessly. Similarly, if the 
# input gif is 37 frames it will still output a gif of 36 frames and won't 
# loop seamlessly.

# get width and height of the input image
width=`convert $1 -coalesce -flatten -format "%[fx:w]" info:`
height=`convert $1 -coalesce -flatten -format "%[fx:h]" info:`

inputfile=$(basename -- "$1")
extension="${inputfile##*.}"

# generate random number for blur
blur=$(echo $((5 + (RANDOM % 20))))

# generate random number for the frquency of the sinusoid function
frequency=$(echo $((1 + (RANDOM % 5))))

# I mostly stole this bit from here https://www.imagemagick.org/Usage/canvas/#random_ripples

for i in `seq 0 10 359`; do
	j=`expr $i \* 5`
	convert \( -size "$width"x"$height" xc: +noise Random \) \
		-channel G \
		-function Sinusoid 1,${i} \
		-virtual-pixel tile -blur 0x10 -auto-level \
		-function Sinusoid 2.5,${j} \
		-separate +channel miff:-
	done |	convert miff:- -set delay 12 -loop 0 displacement_map.gif

# and here all parts are composited into the output gif 
convert \
	-dispose background \
	\( $1 -coalesce \) null: \
	displacement_map.gif \
	-compose displace \
	-define compose:args=30x40 \
	-layers composite \
	${inputfile%.*}_liquid."$extension"
	
# clean up temporary files
rm displacement_map.gif