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dps(1) -- a DjVu to PDF converter

SYNOPSIS

dpsprep [options] src [dest]

DESCRIPTION

This tool, initially made specifically for use with Sony's Digital Paper System (DPS), is now a general-purpose DjVu to PDF converter with a focus on small output size and the ability to preserve document outlines (e.g. TOC) and text layers (e.g. OCR).

OPTIONS

  • -q, --quality: Quality of images in output. Used only for JPEG compression, i.e. RGB and Grayscale images. Passed directly to Pillow and to OCRmyPDF's optimizer.
  • -v, --verbose: Display debug messages.
  • -o, --overwrite: Overwrite destination file.
  • -w, --preserve-working: Preserve the working directory after script termination.
  • -d, --delete-working: Delete any existing files in the working directory prior to writing to it.
  • -t, --no-text: Disable the generation of text layers. Implied by --ocr.
  • -p, --pool-size : Size of MultiProcessing pool for handling page-by-page operations.
  • -m, --mode <infer|bitonal|grayscale|rgb>: Override the image modes encoded in the DjVu file for individual pages. It sometimes makes sense to force bitonal images since they compress well.
  • --dpi : Override DPI values encoded in the DjVu file for individual pages.
  • --ocr : Perform OCR via OCRmyPDF rather than trying to convert the text layer. If this parameter has a value, it should be a JSON dictionary of options to be passed to OCRmyPDF.
  • -O1: Use the lossless PDF image optimization from OCRmyPDF (without performing OCR).
  • -O2: Use the PDF image optimization from OCRmyPDF.
  • -O3: Use the aggressive lossy PDF image optimization from OCRmyPDF.
  • --help: Show help message and exit.
  • --version: Show the version and exit.

EXAMPLES

Produce file.pdf in the current directory:

dpsprep /wherever/file.djvu

Produce output.pdf with reduced image quality and aggressive PDF image optimizations:

dpsprep ---quality=30 -O3 input.djvu output.pdf

Produce an output file using a large pool of workers:

dpsprep --pool=16 input.djvu

Force bitonal images:

dpsprep --mode bitonal input.djvu

Produce an output file by disregarding the text layer and running OCRmyPDF instead:

dpsprep --ocr '{"language": ["rus", "eng"]}' input.djvu

Or simply disregard the text layer without OCR:

dpsprep --no-text input.djvu

NOTE REGARDING COMPRESSION

We perform compression in two stages:

  • The first one is the default compression provided by Pillow. For bitonal images, the PDF generation code says that, if libtiff is available, group4 compression is used.

  • If OCRmyPDF is installed, its PDF optimization can be used via the flags -O1 to -O3 (this involves no OCR). This allows us to use advanced techniques, including JBIG2 compression via jbig2enc.

If manually running OCRmyPDF, note that the optimization command suggested in the documentation (setting --tesseract-timeout to 0) may ruin existing text layers. To perform only PDF optimization you can use the following undocumented tool instead:

python -m ocrmypdf.optimize <input_file> <level> <output_file>