Combining Scanned Images into a PDF with OCR on Mac OS X

Combining Scanned Images into a PDF with OCR on Mac OS X

This guide will walk you through the process of combining multiple scanned images of book pages into a single PDF file on Mac OS X and using OCR (Optical Character Recognition) to convert the text into searchable, selectable electronic text.

1. Installing Required Tools

First, we need to install a few tools to handle image and PDF processing, as well as perform OCR. The following tools are required:

• ImageMagick: For image format conversion and processing.
• ocrmypdf: For performing OCR on PDF files.
• Tesseract: OCR engine used for text recognition.
• Poppler: A PDF utilities suite, which includes tools like pdfunite for merging PDFs.

Install these tools using Homebrew:

brew install imagemagick    # Install ImageMagick
brew install ocrmypdf       # Install OCRMyPDF
brew install tesseract-lang # Install Tesseract language packs
brew install poppler        # Install Poppler

2. Merging Images into a PDF

If your scanned output is in image format (e.g., JPG), you can use ImageMagick to combine multiple image files into a single PDF document. This ensures that the subsequent OCR process works on a single PDF file.

To combine all .jpg images in the current directory into a single 001.pdf file:

magick *.jpg 001.pdf

This command uses the magick tool from ImageMagick to merge all .jpg files in the directory into one PDF file named 001.pdf.

3. Running OCR on the PDF

Next, we use the ocrmypdf tool to perform OCR on the generated PDF file and save the output as a new file. In this step, we specify the OCR languages as English (eng) and Traditional Chinese (chi_tra).

Run the following command:

ocrmypdf -l eng+chi_tra+chi_tra_vert 001.pdf 001a.pdf

This command will apply OCR to the 001.pdf file and save the result as 001a.pdf. The -l eng+chi_tra+chi_tra_vert option indicates that both English and Traditional Chinese will be used for text recognition.

4. Merging Multiple OCR Processed PDFs

If you have multiple PDF files that need to be combined into a single final PDF, the pdfunite tool can do this easily. To merge the processed PDF files into a single output named combined_pdf.pdf, use the following command:

pdfunite 001a.pdf 002a.pdf 003a.pdf combined_pdf.pdf

This command merges 001a.pdf, 002a.pdf, and 003a.pdf into a single combined_pdf.pdf file.

Summary

By following these steps, you can:

1. Merge scanned images into a PDF file.
2. Use the Tesseract engine via ocrmypdf to perform OCR text recognition.
3. Combine multiple PDF files into a final merged PDF.

This allows you to convert scanned images of book pages into a searchable, selectable, and copyable PDF document.