OCRmyPDF — Image Processing Guide

Overview

OCRmyPDF includes powerful image processing capabilities to improve scan quality before OCR. These tools help fix skewed pages, remove noise, clean borders, and enhance readability.

For core OCR functionality, see the ocrmypdf skill. For optimization and PDF/A options, see ocrmypdf-optimize. For batch/Docker/scripting, see ocrmypdf-batch.

Deskew

Deskew corrects pages that are slightly rotated (e.g., from feed scanner skew).

# Auto deskew (recommended)
ocrmypdf --deskew input.pdf output.pdf

# Force deskew even if rotation is minimal
ocrmypdf --deskew --force-ocr input.pdf output.pdf

Rotation

Rotate pages to correct upside-down or sideways scans:

# Auto-rotate based on text orientation
ocrmypdf --rotate-pages input.pdf output.pdf

# Force rotate all pages
ocrmypdf --rotate-pages --force-ocr input.pdf output.pdf

Remove Borders / Cleaning

Remove unwanted borders, artifacts, and noise from scanned pages:

# Remove borders (dots, solid borders)
ocrmypdf --remove-bordering input.pdf output.pdf

# Combine with cleanup
ocrmypdf --remove-bordering --clean input.pdf output.pdf

Despeckle

Remove speckles and isolated noise pixels:

# Remove speckles
ocrmypdf --despeckle input.pdf output.pdf

# Aggressive despeckle for very noisy scans
ocrmypdf --despeckle --clean input.pdf output.pdf

Unpaper

unpaper provides advanced post-processing:

# Apply unpaper with default settings
ocrmypdf --unpaper input.pdf output.pdf

# Custom unpaper board options
ocrmypdf --unpaper-args "--board A4" input.pdf output.pdf

Oversampling

Increase image resolution before OCR for better accuracy:

# Oversample to 300 DPI before OCR
ocrmypdf --oversample 300 input.pdf output.pdf

# Common for low-resolution scans
ocrmypdf --oversample 400 input.pdf output.pdf

Combined Recipes

Fix a skewed scan

ocrmypdf --deskew --remove-bordering --despeckle scanned.pdf fixed.pdf

Clean up a very noisy scan

ocrmypdf --deskew --rotate-pages --despeckle --clean --oversample 300 noisy.pdf clean.pdf

Remove all artifacts

ocrmypdf --remove-bordering --unpaper --despeckle dirty.pdf clean.pdf

Quick Reference

Task	Command
Auto deskew	--deskew
Auto rotate	--rotate-pages
Remove borders	--remove-bordering
Remove speckles	--despeckle
Unpaper	--unpaper
Oversample DPI	--oversample N

Troubleshooting

• Poor OCR after cleaning: Try --oversample 300 to increase input quality.
• Artifacts remain: Use --unpaper for aggressive cleanup.
• Over-cleaned image: Reduce cleaning options for preserve original quality.