Recrops images to 16:9 resolution, either in 1080p (1920 x 1080), 1440p (2560 x 1440) or 4K (3840 x 2160).

recrop16-9.sh

/#!/usr/bin/bash

# Recrops images in working directory to 16:9 resolution.
# Picks the smallest resolution which fits the image with minimal cropping.

OUTPUT_DIR="recropped"
EXT="jpg"

mkdir -p "$OUTPUT_DIR"

for file in *.$EXT; do
    echo "$OUTPUT_DIR/$file"
    touch "$OUTPUT_DIR/$file"
    WIDTH=`identify -ping -format "%w" "$file"`
    HEIGHT=`identify -ping -format "%h" "$file"`
    let "IDEAL_WIDTH = $HEIGHT * 16 / 9"
    let "IDEAL_HEIGHT = $WIDTH * 9 / 16"

    echo $WIDTH, $HEIGHT, $IDEAL_WIDTH, $IDEAL_HEIGHT

    # Max height / width restrictions
    if [ "$WIDTH" -gt 3840 ] || [ "$HEIGHT" -gt 2160 ]; then
        convert "$file" -background black -gravity center -extent 3840x2160 -flatten "$OUTPUT_DIR/$file"
    # Too wide -> add black bars on top / bottom
    elif [ $IDEAL_WIDTH -ge $WIDTH ]; then
        convert "$file" -background black -gravity center -extent "${IDEAL_WIDTH}x${HEIGHT}" -flatten "$OUTPUT_DIR/$file"
    # Too narrow -> add black bars on sides
    else
        convert "$file" -background black -gravity center -extent "${WIDTH}x${IDEAL_HEIGHT}" -flatten "$OUTPUT_DIR/$file"
    fi


    ## Old algorithm: resize to standard sizes of 1080p, 1440p, 4K
    # if [ "$WIDTH" -gt 2560 ] || [ "$HEIGHT" -gt 1440 ]; then
    #     convert "$file" -background black -gravity center -extent 3840x2160 -flatten "$OUTPUT_DIR/$file"
    # elif [ "$WIDTH" -gt 1920 ] || [ "$HEIGHT" -gt 1080 ]; then
    #     convert "$file" -background black -gravity center -extent 2560x1440 -flatten "$OUTPUT_DIR/$file"
    # else
    #     convert "$file" -background black -gravity center -extent 1920x1080 -flatten "$OUTPUT_DIR/$file"
    # fi
done