Loop through a barcode grayscale image with different threshold values and tries to read them. Requires imagemagick and zbarimg.

threshold.sh

#!/bin/bash
# This script will run zbarimg on a thresholded image
# for a range of threshold values.

usage() {
  echo "Usage: $0 <filename> [-s <symbology>] [-a <start_threshold>] [-o <stop_threshold>]"
  echo "  <filename>              Required. Specifies the input file name"
  echo "  -s, --symbology         Optional. Specifies the symbology type"
  echo "  -a, --start-threshold   Optional. Specifies the start threshold (default: 45)"
  echo "  -o, --stop-threshold    Optional. Specifies the stop threshold (default: 55)"
  exit 1
}

PARAMS=""
while (( "$#" )); do
  case "$1" in
    -f|--filename)
      if [ -n "$2" ] && [ ${2:0:1} != "-" ]; then
        FILENAME=$2
        shift 2
      else
        echo "Error: Argument for $1 is missing" >&2
        exit 1
      fi
      ;;
    -s|--symbology)
      if [ -n "$2" ] && [ ${2:0:1} != "-" ]; then
        SYMBOLOGY=$2
        shift 2
      else
        echo "Error: Argument for $1 is missing" >&2
        exit 1
      fi
      ;;
    -a|--start_threshold)
      if [ -n "$2" ] && [ ${2:0:1} != "-" ]; then
        START_THRESHOLD=$2
        shift 2
      else
        echo "Error: Argument for $1 is missing" >&2
        exit 1
      fi
      ;;
    -o|--stop_threshold)
      if [ -n "$2" ] && [ ${2:0:1} != "-" ]; then
        STOP_THRESHOLD=$2
        shift 2
      else
        echo "Error: Argument for $1 is missing" >&2
        exit 1
      fi
      ;;
    --) # end argument parsing
      shift
      break
      ;;
    -*|--*=) # unsupported flags
      echo "Error: Unsupported flag $1" >&2
      exit 1
      ;;
    *) # preserve positional arguments
      PARAMS="$PARAMS $1"
      shift
      ;;
  esac
done

# set positional arguments in their proper place
eval set -- "$PARAMS"
FILENAME="$1"
# check if filename was provided
if [ -z "$FILENAME" ]; then
  echo "Error: filename is a required argument" >&2
  exit 1
fi

# set defaults for start and stop thresholds
START_THRESHOLD=${START_THRESHOLD:-45}
STOP_THRESHOLD=${STOP_THRESHOLD:-55}

echo "Filename: $FILENAME"
echo "Symbology: $SYMBOLOGY"
echo "Start threshold: $START_THRESHOLD"
echo "Stop threshold: $STOP_THRESHOLD"
echo "Positional arguments: $@"

if [[ -n "$SYMBOLOGY" ]]; then
    SYMBOL_OPTS="-Sdisable -S${SYMBOLOGY}.enable"
fi

for i in $(seq "$START_THRESHOLD" "$STOP_THRESHOLD"); do
    echo "Running $i"
    convert "$FILENAME" -threshold "$i"% threshold_"$i".png
    #shellcheck disable=SC2086
    zbarimg --quiet --raw $SYMBOL_OPTS threshold_"$i".png
    if [[ $? -eq 0 ]]; then
        echo "Found at threshold $i"
        break
    fi
done