pdf-invert 0.1.0

Vector-preserving dark-mode (colour inversion) for PDFs

pdf-invert

Convert a PDF into a dark-mode version by inverting its colours — without rasterizing. Text stays selectable and searchable, vector graphics stay vector, and the file stays roughly the same size.

$ uvx pdf-invert paper.pdf
Wrote paper-dark.pdf

Usage

pdf-invert INPUT [-o OUTPUT] [--invert-images] [--linearize] [-q]

• INPUT — the source PDF.
• -o, --output — destination (default: <name>-dark.pdf beside the input).
• --invert-images — also invert raster images. Off by default so photos, figures, and logos don't become negatives.
• --linearize — linearize output for faster web viewing.
• -q, --quiet — suppress warnings.

How it works

For every colour-setting operator in every content stream (page bodies, form XObjects, tiling patterns, Type3 glyphs, annotation appearances), each channel value v is replaced with 1 - v, and a black backdrop is placed behind the page. Because only colours change, the text and vector geometry are untouched.

A few deliberate choices make this robust on real documents — establishing white as the default colour (so text drawn without an explicit colour doesn't vanish on the black backdrop), tracking the current colourspace so sc/scn are only inverted when that's meaningful, visiting shared objects once, and never entering soft masks. See KNOWN_LIMITATIONS.md for what's out of scope.

Why not Ghostscript / rasterizing?

Ghostscript's setcolortransfer inverts at the render pipeline and is excellent, but it needs a system binary and inverts everything, including images. A rasterize-and-invert approach loses selectable text and bloats file size (often 20×). pdf-invert is pure Python (pikepdf), installs anywhere uv/pip reaches, keeps text, and lets you preserve images.

Development

uv run pdf-invert some.pdf      # run from source