ImageMagick-based pseudo-HDR merger script

pseudohdr.sh

#!/bin/bash

# Photos must be perfectly aligned
# Warning: slow
# Created by amateur, don't expect much.

k=0

D=pseudohdr_data

rm -Rf $D/
mkdir -p $D

set -e

INPUTFILES=""
FORMULA_NUMERATOR="0"
FORMULA_DENOMINATOR="0.0001"

for i in "$@"; do 
    echo "Converting $i to png"
    convert "$i" -quality 0  $D/input_$k.png
    echo "Deducing exposure for $i"
    convert $D/input_$k.png -scale 1x1 txt: | \
            perl -ne '/^\s*0\s*,\s*0\s*:\s*\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)[0-9,\s.]*\)/ and print $1+$2+$3,"\n"' | \
            perl -ne '$_+=0.0001; $_ =  533.555424592237/$_ - atan2(590.948204361954, $_); print "$_\n"' \
            > $D/exposure_$k.txt
    echo "Making intermediate picture $k"
    convert $D/input_$k.png \
        -channel A -fx 'lightness*(1-lightness)*4' \
        -channel RGB -fx "u*sqrt($(<$D/exposure_$k.txt))" \
        -quality 0 $D/intermediate_$k.png        
    # -blur 2x3
        
    INPUTFILES+=" $D/intermediate_$k.png"
    FORMULA_NUMERATOR+=" + u[$k]*u[$k].a"
    FORMULA_DENOMINATOR+=" + u[$k].a"
    
    k=$((k+1))
done

echo "Making final picture of $k pieces: output.png"

convert $INPUTFILES  \
    -channel RGB -fx "($FORMULA_NUMERATOR ) / ( $FORMULA_DENOMINATOR )" \
    -channel A -fx 'not(not(a))' \
    -quality 0 output.png

echo Done