bash shell script two variables in for loop

Question

I am new to shell scripting. so kindly bear with me if my doubt is too silly.

I have png images in 2 different directories and an executable which takes an images f

Answer 1

Another solution. The two lists with filenames are pasted into one.

paste <(ls --quote-name ~/prev1/*.png) <(ls --quote-name ~/prev3/*.png) | \
while read args ; do
  run_black $args
done