A Bash script to crop 9 images and create a 3x3 montage using ImageMagick

crop9_montage3x3.sh

#!/bin/bash
#
# ./crop9_montage3x3.sh souryoku_20250502/char 1265x1265+1422+366 result_char.png
# ./crop9_montage3x3.sh souryoku_20250502/mamono 1284x1284+1323+169 result_mamono.png
#

# Get the absolute path to the script's directory and set tmp directory
SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
TMP_DIR="$SCRIPT_DIR/tmp"

# Argument check
if [ -z "$1" ] || [ -z "$2" ]; then
  echo "\nError: Missing required arguments.\n" >&2
  echo "Usage: $0 <image_directory> <crop_param> [output_file]" >&2
  echo "Example: $0 souryoku_20250502/char 1265x1265+1422+366 [output.png]" >&2
  echo "\n  <image_directory> : Directory containing 9 images (sorted by filename)" >&2
  echo "  <crop_param>     : Crop parameter, e.g., 1265x1265+1422+366" >&2
  echo "  [output_file]    : (Optional) Output file name, default is result.png" >&2
  exit 1
fi
IMG_DIR="$1"
CROP_PARAM="$2"
OUTPUT_FILE="${3:-result.png}"

# 1. Get the first 9 files sorted by filename
files=($(ls "$IMG_DIR" | sort | head -n 9))

# 2. Crop each image and save to tmp directory
for i in "${!files[@]}"; do
  convert "$IMG_DIR/${files[$i]}" -crop "$CROP_PARAM" +repage "$TMP_DIR/crop_$i.png"
done

# 3. Combine the 9 cropped images into a 3x3 grid
montage "$TMP_DIR"/crop_{0..8}.png -tile 3x3 -geometry +0+0 "$OUTPUT_FILE"

# 4. Remove temporary cropped images
rm "$TMP_DIR"/crop_{0..8}.png