Script to vectorise images on Linux OS using Potrace. Use cases include scanned pages. Reduces image file size 👍.

vectoriseImages.sh

#!/bin/bash

# exit immediately when:
#  - a command fails
#  - undeclared variables are used
set -o errexit -o nounset

# error codes
OS_ERR=1
GETOPT_FAIL=2
WRONG_ARGS=3
PROG_ERR=4

if [[ "$OSTYPE" != "linux-gnu"* ]]; then
    echo 'ERROR: Script to be run only on Linux'
    exit $OS_ERR
fi

usage()
{
    echo "Usage: $0 [-b|--blacklevel <black_level>][-t|--turdsize <turd_size>][-r|--rotation <angle>][<inputFileName>]

Args:
 black_level: no. b/w 0 and 1.
 turd_size: no. higher than 0.
 angle: no. b/w 0 and 360 degrees.
 inputFileName: if not provided, then the script is run for everything in current directory

Flags:
 --blacklevel: if not provided, default value of black_level is 0.5.
 --turdsize: if not provided, default value of turd_size is 2.
 --rotation: if not provided, default value of angle is 0."
}

# make sure getopt is working
! getopt --test > /dev/null 
if [[ ${PIPESTATUS[0]} -ne 4 ]]; then
    echo 'ERROR: `getopt --test` failed in this environment.'
    exit $GETOPT_FAIL
fi

# parse args
OPTIONS=b:t:r:
LONGOPTS=blacklevel:,turdsize:,rotate:
! PARSED=$(getopt --options=$OPTIONS --longoptions=$LONGOPTS --name "$0" -- "$@")
if [[ ${PIPESTATUS[0]} -ne 0 ]]; then
    echo 'ERROR: Wrong arguments'
    usage
    exit $WRONG_ARGS
fi

# read the output from getopt this way to handle the quoting right:
eval set -- "$PARSED"
black_level=0.5
turd_size=2
rotation=0
while true; do
    case "$1" in
        -b|--blacklevel)
	    black_level="$2"
	    shift 2
	    ;;
	-t|--turdsize)
	    turd_size="$2"
	    shift 2
	    ;;
	-r|--rotate)
	    rotation="$2"
	    shift 2
	    ;;
	--)
	    shift
	    break
	    ;;
	*)
            echo "Programming error"
            exit $PROG_ERR
            ;;
    esac
done

isIntegerGreaterThanZero()
{
    regex='^[0-9]+$';
    if [[ $1 =~ $regex ]]; then
	true
    else
	false
    fi
}

isNumberBetweenZeroAndOne()
{
    if isIntegerGreaterThanZero $1 && ( (( $1 == 0)) || (( $1 == 1)) ); then
        true
        return
    fi

    regex='^[0-9]+\.[0-9]*$';
    if [[ $1 =~ $regex ]]; then
        true
    else
        false
    fi
}

# check validity of args
if ! isIntegerGreaterThanZero $turd_size ; then
    echo 'ERROR: parameter for <-t|--turdsize> must be positive integer'
    usage
    exit $WRONG_ARGS
fi

if ! isIntegerGreaterThanZero $rotation ; then
    echo 'ERROR: parameter for <-r|--rotation> must be positive integer'
    usage
    exit $WRONG_ARGS
fi

if (( rotation > 360 )); then
    echo 'ERROR: parameter for <-r|--rotation> must be in degrees b/w 0 and 360'
    usage
    exit $WRONG_ARGS
fi

if ! isNumberBetweenZeroAndOne $black_level ; then
    echo 'ERROR: parameter for <-b|--black_level> must be a number b/w 0 and 1'
    usage
    exit $WRONG_ARGS
fi

# handle non-option arguments
if [[ $# -eq 0 ]]; then
    FILES_TO_VECTORISE=*
else
    FILES_TO_VECTORISE="$@"
fi

# install programs if uninstalled
if ! loc="$(type -p "potrace")" || [[ -z $loc ]]; then
    sudo apt-get update
    sudo apt-get install potrace
fi

if ! command -v pdftoppm -png $FILES_TO_VECTORISE &> /dev/null; then
    sudo apt-get update
    sudo apt-get install poppler-utils
fi

something_to_vectorise=false

# finally, vectorise
for file in $FILES_TO_VECTORISE; do
    if [ ${file#*.} == "pdf" ]; then
        pdftoppm -png ${file} "${file%%.*}"
        mv "${file%%.*}-1.png" "${file%%.*}.png"
        file="${file%%.*}.png"
    fi

    if [ ${file#*.} != "jpg" ] && [ ${file#*.} != "png" ] ; then
        continue
    fi

    # convert to tmp file usable by potrace
    convert ${file} "${file%%.*}.ppm"

    # now, vectorise
    potrace --svg --rotate $rotation --turdsize $turd_size --blacklevel $black_level "${file%%.*}.ppm"

    # remove tmp file
    rm "${file%%.*}.ppm"

    something_to_vectorise=true

    # check if filesize of svg is smaller than that of img
    non_vectorised_filesize=$(stat -c%s "$file")
    vectorised_filesize=$(stat -c%s "${file%%.*}.svg")
    if (( vectorised_filesize > non_vectorised_filesize )); then
        echo "WARNING: Vectorised file size ($vectorised_filesize bytes) is greater than pre-vectorised file size ($non_vectorised_filesize bytes) for $file"
    fi
done

if [ "$something_to_vectorise" = false ] ; then
    echo 'No files (.jpg, .png, .pdf) to vectorise.'
fi

echo 'End of script'