HOW TO CREATE A LINUX BASH SCRIPT TO CONVERT PDF TO PNG

I needed to find a way to convert over 100 PDF files to PNG and make sure the files PNG were compressed and as small as possible. After doing some research and asking ChatGPT, I was able to get it working by using the below bash Linux script. There are online tools available to assist with conversions, but I desired more control over the process, particularly for a large number of files requiring conversion. To summarise, these were the Linux tools that were needed to complete this task:

• install pdftoppm (sudo apt-get install poppler-utils)
• install convert (sudo apt-get install imagemagick)
• install pngquant (sudo apt-get install pngquant)

Some of the requirements were:

• convert to the PDF file to a max resolution of 2384×3370
• if the filesize was greater than 2 MB then run the compressions
• use a quality of 80 for the compression
• ability to enter the folder name as an input argument

#!/bin/bash

# Check if the folder name is provided as an argument
if [ -z "$1" ]; then
    echo "Usage: $0 <folder_name>"
    exit 1
fi

# Set input folder and output folder based on the argument
input_folder="$1"
output_folder="${input_folder}-new"

# Create output directory if it doesn't exist
mkdir -p "$output_folder"

# Initialize variables
failed_files=()
conversion_summary=()
total_converted=0
max_filesize=2097152  # 2 MB in bytes

# Loop through all PDF files in the input folder
for pdf_file in "$input_folder"/*.pdf; do
    # Get the base filename without extension
    filename=$(basename "$pdf_file" .pdf)
    
    # Display status message before conversion
    echo "Converting $pdf_file to $output_folder/$filename.png..."
    
    # Convert the PDF to PNG using pdftoppm (multiple files are generated per page)
    pdftoppm "$pdf_file" "$output_folder/$filename" -png
    
    # Check if the conversion was successful
    if [ $? -eq 0 ]; then
        # Rename first page if present (remove the -1 suffix)
        first_page_png="$output_folder/$filename-1.png"
        final_png="$output_folder/$filename.png"
        
        if [ -f "$first_page_png" ]; then
            mv "$first_page_png" "$final_png"
        fi
        
        # Handle all the PNG files (including the renamed one)
        for png_file in "$output_folder/$filename"-*.png "$final_png"; do
            # Check if file exists before processing
            if [ -f "$png_file" ]; then
                # Get the PNG image size and file size
                dimensions=$(identify -format "%wx%h" "$png_file")
                filesize=$(stat -c%s "$png_file")

                # Check if the dimensions exceed 2384x3370
                if [[ $(echo "$dimensions" | awk -Fx '{print $1}') -gt 2384 || $(echo "$dimensions" | awk -Fx '{print $2}') -gt 3370 ]]; then
                    echo "Resizing $png_file to 2384x3370..."
                    convert "$png_file" -resize 2384x3370 "$png_file"
                    echo "Resized: $png_file"
                fi
                
                # Adjust quality only if file size exceeds 2 MB
                if [ "$filesize" -gt "$max_filesize" ]; then
                    echo "Setting quality to 80 for $png_file (File size: $filesize bytes)..."
                    convert "$png_file" -quality 80 "$png_file"
                    # Update filesize after adjusting quality
                    filesize=$(stat -c%s "$png_file")
                fi

                # Compress PNG using pngquant
                echo "Compressing $png_file using pngquant..."
                pngquant --quality=80-80 --ext .png --force "$png_file"
                
                # Report final dimensions and file size
                dimensions=$(identify -format "%wx%h" "$png_file")
                filesize=$(stat -c%s "$png_file")
                
                echo "Successfully converted: $filename.pdf"
                echo "Output: $png_file | Dimensions: $dimensions | File size: ${filesize} bytes"
                
                # Add to conversion summary
                conversion_summary+=("$png_file | Dimensions: $dimensions | File size: ${filesize} bytes")
                total_converted=$((total_converted + 1))
            fi
        done
    else
        echo "Failed to convert: $filename.pdf"
        failed_files+=("$pdf_file")
    fi
done

# Display summary of failed conversions
if [ ${#failed_files[@]} -ne 0 ]; then
    echo "The following files failed to convert:"
    for failed_file in "${failed_files[@]}"; do
        echo "$failed_file"
    done
else
    echo "All files converted successfully!"
fi

# Summary of all conversions
echo -e "\n--- Conversion Summary ---"
for summary in "${conversion_summary[@]}"; do
    echo "$summary"
done

# Display total number of files converted
echo "Total files converted: $total_converted"

The end result was very surprising since I thought convert was compressing the file really well and that pngquant wouldn’t do much. Here’s a file size comparison before and after using pgnquant:

It’s important to note that most of the images saw savings of over 50%. You might be concerned about the quality, given that it was adjusted to 80, but I couldn’t notice any difference. I might modify the requirements to convert all files instead of checking if the file size is greater than 2 MB.

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Marco Tran

I am an entrepreneur based in Sydney Australia. I was born in Vietnam, grew up in Italy and currently residing in Australia. I started my first business venture Advertise Me from a random idea and have never looked back since. My passion is in the digital space, affiliate marketing, fitness and I launched several digital products. You will find these on the portfolio page.

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