Compressing comic books (CBR, CBZ files) via the command line (on macos)

README.md

Comic Book Compression Script

A Bash script that compresses CBR and CBZ comic book files by converting images to WebP format while maintaining optimal quality and proper aspect ratios for two-page spreads.

Features

• Supports both CBR, CBZ and PDF formats - Extracts and repacks comic books
• WebP conversion - Reduces file size by 80-90% while maintaining good quality
• Smart two-page spread detection - Maintains proper height for wide images
• Configurable quality and size - Adjust compression settings as needed
• Multiple conversion methods - Uses cwebp when available, falls back to sips
• Cross-platform - Works on macOS with Homebrew packages

Requirements

Required Tools

• 7-Zip - For extracting CBZ files and creating new archives

  brew install sevenzip

• unrar - For extracting CBR files

  brew install carlocab/personal/unrar

• pdftoppm - For extracting PDF files

Optional Tools (Recommended)

• WebP - For better WebP conversion quality

  brew install webp

• bc - For precise aspect ratio calculations

  brew install bc

• ImageMagick - For better image dimension detection

  brew install imagemagick

Installation

1. Download the script:

   curl -O https://gist.githubusercontent.com/your-username/your-gist-id/raw/compress_comics.sh

2. Make it executable:

   chmod +x compress_comics.sh

3. Install required dependencies:

   brew install sevenzip carlocab/personal/unrar webp bc imagemagick

Usage

./compress_comics.sh <comic_file.cbr|.cbz> [quality]

Parameters

• comic_file: CBR or CBZ file to compress (required)
• quality: WebP quality from 1-100 (optional, default: 75)
  • Higher values = better quality, larger files
  • Recommended: 85-95 for high quality, 65-80 for balanced, 40-60 for small files

Examples

# Compress with default quality (75)
./compress_comics.sh "My Comic Book.cbr"

# Compress with high quality (90)
./compress_comics.sh "My Comic Book.cbr" 90

# Compress with smaller file size (60)
./compress_comics.sh "Another Comic.cbz" 60

The script will create a new file with _optimized_webp_q{quality}.cbz suffix in the same directory as the original file.

Configuration

You can modify these variables at the top of the script:

TARGET_HEIGHT=1800  # All images scaled to this height
WEBP_CONVERSION_METHOD="cwebp"  # "cwebp" or "sips"

Note: WebP quality is now controlled via the command line parameter rather than editing the script.

How It Works

1. Extraction - Uses unrar for CBR files, 7zz for CBZ files
2. Image Analysis - Detects image dimensions and aspect ratios
3. Consistent Height Scaling - All images (covers, regular pages, spreads) are scaled to the same height for uniform appearance
4. WebP Conversion - Converts all images to WebP format with specified quality
5. Progress Tracking - Shows a real-time progress bar during processing
6. Repacking - Creates a new CBZ file with optimized images
7. Cleanup - Removes temporary files

Image Processing

The script processes all images consistently:

• Height Uniformity: All images are scaled to the same height (TARGET_HEIGHT=1800) for consistent appearance
• Aspect Ratio Preservation: Images maintain their original proportions during scaling
• Two-Page Spread Detection: Wide images (aspect ratio > 1.3) are detected for logging purposes but processed the same way
• Progress Display: Shows a visual progress bar with percentage completion

Output

• Original CBR/CBZ: Kept unchanged
• Optimized CBZ: Created with _optimized_webp_q{quality}.cbz suffix
• Typical compression: 80-95% file size reduction depending on quality setting
• Quality: Adjustable from 1-100 via command line parameter

Example Results

Original:  My Comic Book.cbr (800 MB)
Quality 75: My Comic Book_optimized_webp_q75.cbz (50 MB) - 94% reduction
Quality 90: My Comic Book_optimized_webp_q90.cbz (85 MB) - 89% reduction

Troubleshooting

Common Issues

1. "unrar not found"

   brew install carlocab/personal/unrar

2. "7zz not found"

   brew install sevenzip

3. Poor WebP quality

   • Use higher quality parameter (e.g., ./compress_comics.sh file.cbr 90)
   • Install webp for better conversion: brew install webp

4. Two-page spreads look wrong

   • Install bc for better calculations: brew install bc
   • Install imagemagick for better dimension detection: brew install imagemagick

Performance Tips

• Process smaller comics first to test quality settings
• Use SSD storage for faster temporary file operations
• Start with quality 75, then adjust up (90+) or down (60-) based on results
• Higher quality values significantly increase processing time and file size

License

This script is provided as-is for personal use. Feel free to modify and distribute.

Contributing

Improvements and bug fixes are welcome! Please test thoroughly before submitting changes.

compress_comics.sh

#!/bin/bash

# Function to display usage information
usage() {
    echo "Usage: $0 <comic_file.cbr|.cbz|.pdf> [quality]"
    echo "  comic_file: CBR, CBZ, or PDF file to compress"
    echo "  quality:    WebP quality (1-100, default: 75)"
    echo "              Higher values = better quality, larger files"
    echo "              Recommended: 85-95 for high quality, 65-80 for balanced, 40-60 for small files"
    echo ""
    echo "This script extracts CBR files using 'unrar', CBZ files using '7zz', and PDF files using 'pdftoppm'."
    echo "It then re-encodes images to WebP and repacks them into a new CBZ file using '7zz'."
    echo "Requires 'unrar' (brew install carlocab/personal/unrar if mainline fails), 'sevenzip' (brew install sevenzip),"
    echo "and 'poppler' (brew install poppler) for PDF support to be installed."
    echo "For WebP conversion: 'webp' (cwebp) (brew install webp) is recommended, but sips is a fallback."
    exit 1
}

# Check if a file path is provided
if [ -z "$1" ]; then
    usage
fi

COMIC_FILE="$1"
WEBP_QUALITY="${2:-85}"  # Use second argument or default to 85

# Validate quality parameter
if ! [[ "$WEBP_QUALITY" =~ ^[0-9]+$ ]] || [ "$WEBP_QUALITY" -lt 1 ] || [ "$WEBP_QUALITY" -gt 100 ]; then
    echo "Error: Quality must be a number between 1 and 100"
    usage
fi

FILENAME=$(basename "$COMIC_FILE")
DIRNAME=$(dirname "$COMIC_FILE")
BASENAME="${FILENAME%.*}" # File name without extension
EXTENSION="${FILENAME##*.}" # Extension (cbr or cbz)
TEMP_DIR="${DIRNAME}/${BASENAME}_temp_webp_comic_processing"
OUTPUT_FILE="${DIRNAME}/${BASENAME}_optimized_webp_q${WEBP_QUALITY}.cbz"

# --- Configuration for Image Optimization ---
MAX_DIMENSION=1200 # Set the maximum dimension (width or height) for the images
TARGET_HEIGHT=1800 # All images will be scaled to this height


# --- Choose WebP Conversion Method ---
# Set to 'cwebp' to use cwebp (recommended, requires installation)
# Set to 'sips' to use sips (fallback, built-in)
WEBP_CONVERSION_METHOD="cwebp"

echo "🚀 Starting comic book optimization for: ${FILENAME}"
echo "-----------------------------------------------------"

# 1. Check for necessary tools
echo "🔍 Checking for required tools..."
if ! command -v 7zz &> /dev/null; then
    echo "Error: '7zz' (from sevenzip package) is not installed. Please install it using 'brew install sevenzip'."
    exit 1
fi
echo "✅ '7zz' found."

if [ "$EXTENSION" == "cbr" ]; then
    if ! command -v unrar &> /dev/null; then
        echo "Error: 'unrar' is not installed. Please install it using 'brew install carlocab/personal/unrar'."
        exit 1
    fi
    echo "✅ 'unrar' found."
fi

if [ "$EXTENSION" == "pdf" ]; then
    if ! command -v pdftoppm &> /dev/null; then
        echo "Error: 'pdftoppm' is not installed. Please install it using 'brew install poppler'."
        exit 1
    fi
    echo "✅ 'pdftoppm' found."
fi

if [ "$WEBP_CONVERSION_METHOD" == "cwebp" ]; then
    if ! command -v cwebp &> /dev/null; then
        echo "Warning: 'cwebp' not found. Falling back to 'sips' for WebP conversion."
        WEBP_CONVERSION_METHOD="sips"
    else
        echo "✅ 'cwebp' found."
    fi
fi

# Check for bc calculator (for aspect ratio calculations)
if ! command -v bc &> /dev/null; then
    echo "Warning: 'bc' calculator not found. Two-page spread detection may be less accurate."
    echo "Install with: brew install bc"
else
    echo "✅ 'bc' found."
fi

# 2. Create a temporary directory
echo "📂 Creating temporary directory: ${TEMP_DIR}"
mkdir -p "$TEMP_DIR" || { echo "Error: Could not create temporary directory. Exiting."; exit 1; }

# 3. Extract the comic book based on extension
echo "📦 Extracting comic book..."
case "$EXTENSION" in
    cbz)
        # Use 7zz for CBZ (ZIP)
        echo "  Using 7zz to extract CBZ file."
        7zz x "$COMIC_FILE" -o"${TEMP_DIR}/" -y &> /dev/null || { echo "Error: Failed to extract CBZ file with 7zz. Exiting."; rm -rf "$TEMP_DIR"; exit 1; }
        echo "✅ CBZ extracted by 7zz."
        ;;
    cbr)
        # Use unrar for CBR (RAR), fallback to 7zz if it's actually a ZIP file
        echo "  Using unrar to extract CBR file."
        if unrar x -inul "$COMIC_FILE" "$TEMP_DIR" 2>/dev/null; then
            echo "✅ CBR extracted by unrar."
        else
            echo "  unrar failed, trying 7zz (CBR might be a ZIP file)..."
            7zz x "$COMIC_FILE" -o"${TEMP_DIR}/" -y &> /dev/null || { echo "Error: Failed to extract CBR file with both unrar and 7zz. Exiting."; rm -rf "$TEMP_DIR"; exit 1; }
            echo "✅ CBR extracted by 7zz (was actually a ZIP file)."
        fi
        ;;
    pdf)
        # Use pdftoppm for PDF with high DPI for better quality
        echo "  Using pdftoppm to extract PDF file at 300 DPI."
        pdftoppm -png -r 300 "$COMIC_FILE" "${TEMP_DIR}/page" || { echo "Error: Failed to extract PDF file with pdftoppm. Exiting."; rm -rf "$TEMP_DIR"; exit 1; }
        echo "✅ PDF extracted by pdftoppm at 300 DPI."
        ;;
    *)
        echo "Error: Unsupported file type. Only .cbr, .cbz, and .pdf are supported."
        rm -rf "$TEMP_DIR"
        exit 1
        ;;
esac

# 4. Skip the target height calculation - we use a fixed height for all images
echo "📏 Using fixed target height: $TARGET_HEIGHT"

# 5. Process and re-encode images to WebP
echo "🖼️ Re-encoding images to WebP (target height ${TARGET_HEIGHT}, quality ${WEBP_QUALITY})..."

# Count total images first
TOTAL_IMAGES=0
for IMG in "$TEMP_DIR"/*.jpg "$TEMP_DIR"/*.jpeg "$TEMP_DIR"/*.png; do
    [ -f "$IMG" ] && TOTAL_IMAGES=$((TOTAL_IMAGES + 1))
done

# Process images one by one with progress indicator
CURRENT_IMAGE=0
for IMG in "$TEMP_DIR"/*.jpg "$TEMP_DIR"/*.jpeg "$TEMP_DIR"/*.png; do
    # Skip if no files match the pattern
    [ ! -f "$IMG" ] && continue
    CURRENT_IMAGE=$((CURRENT_IMAGE + 1))
    ORIGINAL_IMG="$IMG"
    BASENAME_IMG="${ORIGINAL_IMG%.*}"
    NEW_WEBP_IMG="${BASENAME_IMG}.webp"
    
    # Calculate and display progress
    PROGRESS=$((CURRENT_IMAGE * 100 / TOTAL_IMAGES))
    printf "\r  Progress: [%-50s] %d%% (%d/%d)" "$(printf '%*s' $((PROGRESS / 2)) '' | tr ' ' '=')" "$PROGRESS" "$CURRENT_IMAGE" "$TOTAL_IMAGES"

    # Get image dimensions to detect two-page spreads
    if command -v identify &> /dev/null; then
        # Use ImageMagick if available
        DIMENSIONS=$(identify -format "%w %h" "$ORIGINAL_IMG" 2>/dev/null)
        WIDTH=$(echo $DIMENSIONS | cut -d' ' -f1)
        HEIGHT=$(echo $DIMENSIONS | cut -d' ' -f2)
    else
        # Fallback to sips
        DIMENSIONS=$(sips -g pixelWidth -g pixelHeight "$ORIGINAL_IMG" 2>/dev/null | tail -2 | awk '{print $2}')
        WIDTH=$(echo "$DIMENSIONS" | head -1)
        HEIGHT=$(echo "$DIMENSIONS" | tail -1)
    fi

    # Check if this is a two-page spread (width > height * 1.3)
    if [ -n "$WIDTH" ] && [ -n "$HEIGHT" ] && [ "$WIDTH" -gt 0 ] && [ "$HEIGHT" -gt 0 ]; then
        ASPECT_RATIO=$(echo "scale=2; $WIDTH / $HEIGHT" | bc -l 2>/dev/null || echo "1.0")
        IS_SPREAD=$(echo "$ASPECT_RATIO > 1.3" | bc -l 2>/dev/null || echo "0")
        
        RESIZE_PARAM="0 $TARGET_HEIGHT"  # All images resized to same height
    else
        RESIZE_PARAM="$MAX_DIMENSION 0"  # Default fallback
    fi

    if [ "$WEBP_CONVERSION_METHOD" == "cwebp" ]; then
        cwebp -q $WEBP_QUALITY -resize $RESIZE_PARAM "$ORIGINAL_IMG" -o "$NEW_WEBP_IMG" &> /dev/null || {
            echo "    Warning: Failed to convert $(basename "$ORIGINAL_IMG") to WebP with cwebp. Keeping original format."
            sips -Z $MAX_DIMENSION "$ORIGINAL_IMG" &> /dev/null
            continue
        }
    else # WEBP_CONVERSION_METHOD == "sips"
        # For all images with sips, resize to target height
        # sips doesn't support resize by height only, so we calculate width from aspect ratio
        TARGET_WIDTH=$(echo "scale=0; $WIDTH * $TARGET_HEIGHT / $HEIGHT" | bc 2>/dev/null || echo "$MAX_DIMENSION")
        sips -Z $TARGET_WIDTH "$ORIGINAL_IMG" --setProperty format webp "$NEW_WEBP_IMG" &> /dev/null || {
                echo "    Warning: Failed to convert $(basename "$ORIGINAL_IMG") to WebP with sips. Keeping original format."
                sips -Z $MAX_DIMENSION "$ORIGINAL_IMG" &> /dev/null
                continue
            }
    fi

    # Remove the original image after successful conversion
    rm "$ORIGINAL_IMG"
done
echo ""  # New line after progress bar
echo "✅ Images re-encoded to WebP."

# 5. Repack into a new CBZ file using 7zz (cannot use unrar for compression)
echo "📦 Compressing the re-encoded WebP images into a new CBZ file with 7zz..."
7zz a -tzip -mx=9 "${OUTPUT_FILE}" "${TEMP_DIR}"/* &> /dev/null || { echo "Error: Failed to repack CBZ file with 7zz. Exiting."; rm -rf "$TEMP_DIR"; exit 1; }
echo "✅ New CBZ file created: ${OUTPUT_FILE}"

# 6. Clean up temporary directory
echo "🧹 Cleaning up temporary directory: ${TEMP_DIR}"
rm -rf "$TEMP_DIR"
echo "✅ Cleanup complete."

echo "🎉 Optimization finished! Enjoy your smaller, WebP comic book."
echo "-----------------------------------------------------"