How does veil keep images intact in dark mode?

veil walks the PDF.js operator list to detect image regions, then composites the original image pixels over the inverted background using a second canvas. Photos, charts, histology slides, and microscopy images keep their original colors while text and backgrounds are inverted.

Yes. veil is free and open source under the MIT license. There is no signup, no account, no paid tier. Anyone can fork, modify, or self-host.

Where do my PDFs go when I open them in veil?

Nowhere. veil runs entirely in your browser. PDFs are processed locally on your device and never leave it. The app works offline after the first visit and has no server-side component.

Can I save a dark mode PDF that opens in other readers?

Yes. veil exports a PDF with selectable text, working internal and external links, existing document bookmarks with their hierarchy and destinations, and images preserved in their original colors. The exported file opens correctly in any standard PDF reader on any device.

Does veil work on scanned PDFs?

Yes. veil detects scanned documents automatically and runs OCR in the background via Tesseract.js. The recognized text becomes a selectable layer. Scans with embedded invisible OCR text layers (a format used by some scanning tools) are also detected and inverted correctly.

What does veil do that a dark mode browser extension doesn't?

Browser extensions invert every pixel including images, which destroys photos, charts, and figures. veil detects image regions structurally via the PDF operator list and protects them from inversion. The result is dark mode that respects color-critical content like medical imaging, histology, and scientific figures.

No. veil contains no AI, no machine learning models, no neural networks. Image regions are detected via deterministic operator list walking with a transformation matrix stack. OCR via Tesseract.js is statistical pattern recognition, not generative AI.

Why isn't veil's dark mode pure black?

veil uses invert(0.86) instead of full inversion because pure black backgrounds with pure white text are too harsh for long reading sessions. 0.86 produces a soft dark gray (around #242424) and a slightly muted white (around #DBDBDB), which reduces eye strain on prolonged use.

Dark mode PDFs
without destroying your
histology slides

True dark mode that understands your document.
Text inverted, images kept intact.

Start reading

100% Private / Works Offline

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VEIL

Three layers, one experience

What happens when you drop a PDF

Pure Engineering

PDF.js operator list detects images. Deterministic, inspectable, yours.

Your Device Only

OCR, rendering, export,
all client-side.
Files never leave your browser.

Nothing Lost

Text stays selectable.
Images stay protected.
Already-dark pages left untouched.
Scanned docs get OCR automatically.
Export works in any reader.

Pure Engineering

PDF.js operator list detects images.
Deterministic, inspectable, yours.

Your Device Only

OCR, rendering, export, all client-side.
Files never leave your browser.

Nothing Lost

Text stays selectable, images stay protected. Already-dark pages left untouched. Scanned docs get OCR automatically. Export works in any reader.

Only in veil

OCR on images inside your PDFs

The text in your document is selectable. The text trapped inside images isn't. Until now.

veil scans images inside your document and makes their text selectable. Chart labels, axis numbers, figure captions. Copy them like any other text.

Chart labelsAxis textTable headersFigure captions

Take it with you

Your dark PDF, everywhere. Download with dark mode baked in, open it on any device, send it to anyone.

Export dark PDFs

On desktop, veil exports a dark PDF with selectable, searchable text and high-quality rendering while preserving existing document bookmarks and their hierarchy.

Links preserved

Internal navigation and external references work in the viewer and remain active in exported PDFs, including page links, DOIs, and bibliographic references.

Works offline

Once installed, veil runs offline and continues to process PDFs entirely on your device without an internet connection.

Built for the researcher reading papers at 2 AM, the medical student reviewing slides before rounds, and anyone who thinks a PDF reader should respect both their eyes and their images.

If veil is useful in your reading sessions, feel free to buy me a coffee.

Support veil

Dark mode PDFswithout destroying yourhistology slides

Three layers, one experience

OCR on images inside your PDFs

Take it with you

Dark mode PDFs
without destroying your
histology slides