[Python] Convert multiple-page PDF files to PNG quickly

I have a folder containing 600 PDF files, and each PDF has 20 pages. I need to convert each page into a high-quality PNG as quickly as possible.

I wrote the following script for this task:

import os
import multiprocessing
import fitz # PyMuPDF
from PIL import Image

def process_pdf(pdf_path, output_folder):
try:
pdf_name = os.path.splitext(os.path.basename(pdf_path))[0]
pdf_output_folder = os.path.join(output_folder, pdf_name)
os.makedirs(pdf_output_folder, exist_ok=True)

doc = fitz.open(pdf_path)

for i, page in enumerate(doc):
pix = page.get_pixmap(dpi=850) # Render page at high DPI
img = Image.frombytes("RGB", [pix.width, pix.height], pix.samples)

img_path = os.path.join(pdf_output_folder, f"page_{i+1}.png")
img.save(img_path, "PNG")

print(f"Processed: {pdf_path}")
except Exception as e:
print(f"Error processing {pdf_path}: {e}")

def main():
input_folder = r"E:\Desktop\New folder (5)\New folder (4)"
output_folder = r"E:\Desktop\New folder (5)\New folder (5)"

pdf_files = [os.path.join(input_folder, f) for f in os.listdir(input_folder) if f.lower().endswith(".pdf")]

with multiprocessing.Pool(processes=multiprocessing.cpu_count()) as pool:
pool.starmap(process_pdf, [(pdf, output_folder) for pdf in pdf_files])

print("All PDFs processed successfully!")

if __name__ == "__main__":
main()


Issue:

This script is too slow, especially when processing a large number of PDFs. I tried the following optimizations, but they did not improve speed significantly:

• Reduced DPI slightly – Lowered from 1200 DPI to 850 DPI. (I also tested 600-800 DPI.)
• Enabled alpha=False in get_pixmap() – Reduced memory usage.
• Used ThreadPoolExecutor instead of multiprocessing.Pool – No major improvement.
• Reduced PNG compression – Set optimize=False when saving images.
• Converted images to grayscale – Helped slightly, but I need color images for my task.

Possible Solutions I Considered:

• Parallel Processing of Pages Instead of Files – Instead of processing one file at a time, process each page in parallel to fully utilize CPU cores.
• Use ProcessPoolExecutor instead of ThreadPoolExecutor – Since rendering is CPU-intensive, multiprocessing should be better.
• Use JPEG Instead of PNG – JPEG is much faster to save and takes less storage, but I need high-quality images.
• Lower DPI to 500-600 – Provides a balance between speed and quality.
• Batch Write Files Instead of Saving One by One – Reduces I/O overhead.

What I Need Help With:

• How can I significantly speed up this PDF-to-PNG conversion while maintaining high image quality?
• Are there better libraries or techniques I should use?
• Is there a way to fully utilize CPU cores efficiently?

Any suggestions would be greatly appreciated!

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