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Adding OCR text to a PDF (even a noisy one)
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| # usage: ocr-pdf scanned.pdf | |
| set -euf -o pipefail -o xtrace | |
| INFILE=$1 | |
| BASENAME=$(basename "$1" .pdf) | |
| TIFFFILE=$BASENAME.tiff | |
| OCRDPDFNOEXT=$BASENAME-OCRd-big | |
| OCRDPDF=$OCRDPDFNOEXT.pdf | |
| SMALLEROCRDPDF=$BASENAME-OCRd.pdf | |
| # Make a multipage TIFF of the original PDF ~700MB | |
| gs -o "$TIFFFILE" -sDEVICE=tiff32nc -r300 "$INFILE" | |
| # OCR the TIFF using tesseract4 alpha in docker, store as PDF of images+positioned text ~16MB | |
| docker run --rm -v $PWD:$PWD tesseractshadow/tesseract4re tesseract "$PWD/$TIFFFILE" "$PWD/$OCRDPDFNOEXT" pdf | |
| rm "$TIFFFILE" | |
| # Convert images in PDF to jpeg to reduce size ~4MB | |
| gs -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook -sOutputFile="$SMALLEROCRDPDF" "$OCRDPDF" |
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