Use ImageMagick to trim extra pixels from an image and replace with a uniform border (default 10 pixels); good for screenshots

reborder

#!/usr/bin/env bash
##
##  Trim extra pixels from around an image, e.g., a screenshot, and replace
##  with a border of uniform width, of a color sampled from the four image
##  corners, using ImageMagick 6.x (or above?)
##
##  Author:    Kevin Ernst <ernstki -at- mail.uc.edu>
##  Date:      29 August 2024
##  License:   WTFPL or ISC at your option
##  Homepage:  https://gist.github.com/ernstki/74aba058622a9cea43bebc4028aba5cd
##  Usage:     See the output of `reborder --help` or HELP below
##
##  References:
##    1. https://imagemagick.org/Usage/crop/#border
##    2. https://stackoverflow.com/a/48685590/785213
##
if (( DEBUG )); then
    set -eExo pipefail
    trap 'echo "Trapped at line #$LINENO${FUNCNAME:+ in $FUNCNAME}."' ERR
fi
set -u

ME=${BASH_SOURCE[0]##*/}
HELP="
  $ME - trim extra pixels from an image, then add a border of the same color

    usage:
      $ $ME [-h|--help]
      $ $ME [-f|--force] [-n|--dry-run] [BORDERSIZE] IMAGE [IMAGE…]

    where:
      IMAGE          is any image ImageMagick can handle
      BORDERSIZE     is a valid ImageMagick '-bordersize' (default: 10x10)
      -f, --force    forces overwriting of existing rebordered image(s)
      -n, --dry-run  simulates what would happen; does not modify any images
      -q, --quiet    suppresses \"Wrote 'newimage.ext'.\" messages

    homepage:
      https://gist.github.com/ernstki/74aba058622a9cea43bebc4028aba5cd
"

plurality() {
    # read hex triplet color values and print the one that appears most often
    # or return an error if there's no plurality
    awk '
        { colorcounts[$1]++ }
        END {
            for (c in colorcounts) {
                if (colorcounts[c] > max) {
                    it = c
                    max = colorcounts[c]
                }
            }
            if (max <= NR/2) exit 1
            else print it
        }'
}

images=()
borderwidth=10
force=
# could make an option for this later
fuzz='1%'
suffix='+rebordered'
dryrun=${DRYRUN:-}
quiet=
endofopts=

while (( $# )); do
    if (( endofopts )); then images+=("$1"); shift; continue; fi
    case $1 in
        --)
            endofopts=1
            ;;
        -h|--help)
            echo "$HELP"
            exit
            ;;
        1|1x1|[0-9]*[0-9]|[0-9]*[0-9]x[0-9]*[0-9])
            borderwidth=$1
            ;;
        -f|--force|--force-overwrite)
            force=1
            ;;
        -n|--dryrun|--dry-run)
            dryrun=1
            ;;
        -q|--quiet|--silent)
            quiet=1
            ;;
        *)
            images+=("$1")
            ;;
    esac
    shift
done

if [[ -z ${images[*]} ]]; then
    echo "No images specified to operate on. Try '--help'." >&2;
    exit 1
fi

tl='%[hex:u.p{0,0}]'
tr='%[hex:u.p{w-1,0}]'
bl='%[hex:u.p{0,h-1}]'
br='%[hex:u.p{w-1,h-1}]'
processed=0

for i in "${images[@]}"; do
    if [[ ! -r $i ]]; then
        echo "Unreadable or non-existent file '$i'. Skipping." >&2;
        continue
    fi

    newi="${i%%.*}$suffix.${i##*.}"
    cornerpixels=$(convert "$i" -format "$tl\n$tr\n$bl\n$br\n" info:)

    if (( $? )); then
        echo "Problem running ImageMagick 'convert'; try DEBUG=1" >&2
        exit 1
    fi

    if color=$(echo "$cornerpixels" | plurality); then
        if [[ -s $newi ]] && (( !force && ! dryrun)); then
            read -rp "Image '$newi' already exists. Overwrite it? [y/N] "
            if [[ -z $REPLY || $REPLY =~ ^[nN] ]]; then
                if (( !quiet )); then
                    echo "Not overwriting existing '$newi'." >&2
                fi
                continue
            fi
        fi
        ${dryrun:+echo [DRY RUN] }convert "$i" -trim -fuzz "$fuzz" +repage \
                                          "$newi"
        ${dryrun:+echo [DRY RUN] }mogrify -bordercolor "#$color" -border \
                                          "$borderwidth" "$newi"
        if (( !dryrun && !quiet )); then echo "Wrote '$newi'." >&2; fi
        processed=$(( processed + 1 ))
    else
        echo "Corner pixels of '$i' are too different, can't add a border." \
             "Skipping." >&2
    fi
done

if (( !processed )); then
    echo "No images were processed." >&2;
    exit 1
fi

Installation

Make sure ~/bin is in your search path. These days, it usually is. Then:

GIST=https://gist.github.com/ernstki/74aba058622a9cea43bebc4028aba5cd
SCRIPT=$GIST/raw/reborder
(curl -sL $SCRIPT || wget -qO- $SCRIPT) > ~/bin/reborder
chmod a+x ~/bin/reborder

# test it
which reborder
reborder --help

Example

Running reborder with default settings turns this:

into this:

License

WTFPL or ISC, at your option.