Code:
zenity --list --column='Width' --column='Height" --column="Filename" ${result[@]}
' and " are not interchangeable. i.e --column='Height" will produce an error.
The \ in the example allows you to continue a long command on the next line which also increased readability. It isn't a newline character.
The normal column separator is a space so changing your
Code:
result+=$(identify -format '%w %h "%i"\n' "$f")
Code:
result+=$(identify -format '%w %h "%i" ' "$f")
Should fix your script.