Bash script - why is this script so slow?

Scripting/Programming
#1

Granted the three arrays contain 3x365400 pixel values. But this takes minutes. The same done in PHP takes three seconds including to get the image!

I am not very experienced in bash scripting, so it might have crucial error.

for index in ${!R_pixel_array[@]}; do
      blue_red=bc <<< ${B_pixel_array[index]}-${R_pixel_array[index]}
      green_red=bc <<< ${G_pixel_array[index]}-${R_pixel_array[index]}
      if (( $(echo "$blue_red < 10" |bc -l) )) && (( $(echo "$green_red < 10" |bc -l) )) && (( $(echo "${B_pixel_array[index]} > 100" |bc -l) ))
        then
          ((count=count+1))
      fi
done
#2

Have you tried executing your COMMANDS asynchronously? Run the following to get syntax help

help coproc
#3

Sounds good, but how would you use that in this case?

Btw. CPU is at 60% while comparing the numbers, which sound excessive.

#4

This is not “bash” solution when using bc. I would use awk oneliner and it would be as fast as php.