colour-wash.sh

#!/bin/bash
set -e

if [[ "$1" != /* ]]; then
    # Relative path name
    FILENAME_WITH_EXT=$(basename "$1")
    FILENAME="${FILENAME_WITH_EXT%.*}"
    ABSPATH=$(unset CDPATH && cd "$(dirname "$0")" && echo $PWD)
    DIRNAME="$ABSPATH/$FILENAME"
    FILEEXT="${FILENAME_WITH_EXT##*.}"
    ORIG_FILEPATH="$ABSPATH/$FILENAME_WITH_EXT"
else
    # Absolute path name
    FILENAME_WITH_EXT=$(basename "$1")
    DIRNAME="${1%.*}"
    FILENAME="${FILENAME_WITH_EXT%.*}"
    FILEEXT="${FILENAME_WITH_EXT##*.}"
    ORIG_FILEPATH="$1"
fi

# Create a new directory, new to the original file, for storing new color variants
echo "Creating the output directory"
mkdir -p "$DIRNAME"

NEW_FILEPATH=""
set_new_filepath(){
    local MODIFIER="$1"
    NEW_FILEPATH="$DIRNAME/$FILENAME-$MODIFIER.$FILEEXT"
}

echo "Creating a gray scale version of image"
set_new_filepath "gray"
GRAY_FILEPATH="$NEW_FILEPATH"

# If you want use the image in slides (ie. crop image to 16:9 and make it smaller) :
convert "$ORIG_FILEPATH" -colorspace gray -geometry 1920x1080^ -gravity center -crop 1920x1080+0+0 "$GRAY_FILEPATH"
# If you just want to create colourful version of the original pic (without cropping and etc.) :
# convert "$ORIG_FILEPATH" -colorspace gray "$GRAY_FILEPATH"

COLORS=(
    "rgb(2, 33, 90)"      "rgb(230, 245, 221)"
    "rgb(70, 45, 152)"    "rgb(255, 240, 212)"
    "rgb(79, 16, 89)"     "rgb(238, 243, 245)"
    "rgb(3, 52, 64)"      "rgb(206, 236, 228)"
    "rgb(8, 90, 75)"      "rgb(225, 220, 220)"
    "rgb(56, 157, 70)"    "rgb(255, 244, 179)"
    "rgb(253, 145, 146)"  "rgb(242, 238, 230)"
    "rgb(129, 157, 174)"  "rgb(255, 244, 179)"
    "rgb(252, 84, 71)"    "rgb(238, 243, 245)"
    "rgb(190, 196, 229)"  "rgb(238, 243, 245)"
    "rgb(239, 214, 196)"  "rgb(255, 255, 255)"
    "rgb(225, 220, 220)"  "rgb(255, 255, 255)"
)

printf "%s" "Creating color washed versions of image"
for ((c=0;c<${#COLORS[@]};c=c+2)); do
    printf "%s" "."

    NUMBER=$(($((c/2))+1))
    DARK_COLOR=${COLORS[c]}
    LIGHT_COLOR=${COLORS[c+1]}

    set_new_filepath "gradient"
    GRADIENT_FILEPATH="$NEW_FILEPATH"
    convert \( -size 1x1 xc:"$DARK_COLOR" xc:"$LIGHT_COLOR" +append \) -filter cubic -resize 256x1! -scale 256x20! "$GRADIENT_FILEPATH"

    set_new_filepath "$NUMBER"
    convert "$GRAY_FILEPATH" "$GRADIENT_FILEPATH" -clut "$NEW_FILEPATH"
done
printf "%s\n" " "

# Remove the gradient file, because we don't need that one
echo "Removing temporary files"
rm -f "$GRADIENT_FILEPATH"

echo "All color versions created"