pdf2print 0.1.0

Convert design-heavy PDFs into print-friendly versions via hue-preserving lightness inversion.

print-friendly-pdf

Install

pip install pdf2print

Usage

pdf2print input.pdf
pdf2print input.pdf --dpi 300

Converts design-heavy PDFs (dark backgrounds, white text, colored charts) into print-friendly versions — without destroying chart colors.

Live: https://print-friendly-pdf.indyri.se

Why this exists

Dark-background PDFs are ink-expensive to print. Existing inverters do naive RGB inversion, which makes text readable but flips every chart color (red becomes cyan, orange becomes blue). This tool does neither-or:

1. Hue-preserving lightness inversion. Lightness is inverted in HSL space, which reduces to a closed-form RGB operation: RGB' = RGB + (1 − max(RGB) − min(RGB)). White text becomes black, dark backgrounds become light, and saturated chart colors — which sit near mid-lightness — pass through nearly unchanged. Provably no clipping.

2. Surgical page replacement. Only dark-detected pages are rasterized and replaced. Every other page keeps its original vector content — searchable, sharp, and small. A document with no dark pages is returned byte-identical.

Usage

CLI

python cli.py input.pdf [--dpi 150] [--no-invert]

Writes input_print.pdf alongside the input.

Web

Upload a PDF at the live URL. The converted PDF opens in a new tab with the browser's native print button. Chrome-first.

Known limitations

• Light-panel preservation uses a size threshold. Large white content panels (cards, callout boxes) on dark pages are detected via connected-component analysis and preserved with their original colors. Regions below ~2% of page area (small icons, white text) invert with the page — by design. The threshold is conservative and fails open: if no region qualifies, the page inverts normally.
• Dark-page detection uses corner sampling — centered dark panels on light pages are not detected (v1.5 adds AI classification)
• Replaced pages lose their searchable text layer
• 32MB file ceiling
• Password-protected PDFs not supported

Stack

PyMuPDF, Pillow, numpy, Flask, Python 3.11 · Cloud Run backend · Vercel static frontend · GoDaddy CNAME

License

License

This project is licensed under the MIT License — see LICENSE for details.

Dependency notice: This project uses PyMuPDF (fitz), which is licensed under the GNU AGPL v3. If you deploy this software as a network service, the AGPL requires you to make the complete source code available to users. This repository satisfies that requirement.