paper-as-pair-pngs.sh

#!/bin/bash
pdffile="$1"
prefix=$(basename "${pdffile}" .pdf)

convert -density 300 "${pdffile}" "${prefix}-%03d.png"
mogrify -background white -flatten "${prefix}-*.png"

total_pages=$(ls ${prefix}-*.png | wc -l)
for ((i=0; i<$total_pages; i+=2)); do
    # Format page numbers
    page1=$(printf "${prefix}-%03d.png" $i)
    page2=$(printf "${prefix}-%03d.png" $(($i + 1)))

    # Check if the second page exists
    if [ -f "$page2" ]; then
        output=$(printf "${prefix}-x2-%03d.png" $(($i / 2)))
        convert "$page1" "$page2" +append "$output"
    else
        # If there's no pair for the last page, just copy it as is
        cp "$page1" $(printf "${prefix}-x2-%03d.png" $(($i / 2)))
    fi
done