Invert PDF Colours

1. 1Add the PDF you want to read at night.
2. 2Choose a resolution — Standard is fine for reading on screen.
3. 3Press Invert colours and wait while the pages are processed.
4. 4Download the inverted copy and read it in any viewer.

Every pixel is replaced by its opposite: each of the red, green and blue channels is subtracted from 255. White paper becomes near-black, black text becomes near-white, and the contrast between them is preserved exactly.

Many readers offer a night mode, but it is a viewing setting the file does not carry with it — send the document to a tablet or an e-reader and you are back to a white page. Inverting the file itself means it looks the same everywhere, which is the point.

Photographs invert too, and look like film negatives. For a document that is mostly photographs this is the wrong tool; it suits text documents, papers and slide decks with plain backgrounds. As with any re-rendered page, the text in the result is no longer selectable.

The file is read into your browser's memory, changed there, and handed straight back to you. Nothing is uploaded, so there is no queue and no copy sitting on a server afterwards.

• Use it on text documents, papers and slide decks with plain backgrounds. Photographs come out looking like film negatives.
• Keep the original. The inverted copy is for reading, and its text can no longer be selected.
• Do not print the inverted version — a page that is mostly black uses a great deal of ink or toner.
• If you only read on one device, its reader's night mode may be enough. Inverting the file is for when you want the dark version everywhere.

• How to read PDFs comfortably on a tablet, phone or e-reader
• How to read a PDF in dark mode