How it works

Inverting a page is easy and looks terrible. Here is what we do instead.

The problem with inverting

A naive dark mode flips every colour. White paper becomes black, which is what you wanted, and a photograph of a beach becomes an orange sky over a purple sea, which is not. Charts lose their meaning, brand colours turn into their opposites, and a scanned signature ends up glowing.

Working in perceptual colour

Every colour decision is made in a perceptual colour space rather than raw RGB. That lets us change how light something is while leaving its hue alone. Paper lands exactly on the background of the style you picked, black ink lands exactly on its text colour, and every grey in between rides the same ramp so nothing looks out of place.

Saturated colours are treated differently again. A brand orange or a chart cyan already reads perfectly well on a dark background, so we keep it — and only brighten it if it would otherwise be hard to read. We never make a colour less readable than it was on white, and never artificially louder either, so a faint watermark stays faint.

Pictures are looked at individually

Every image in the document is classified before anything happens to it:

Photographs keep their colours and are gently dimmed so they do not glare on a dark page.
Charts and diagrams keep their data colours while their white background goes dark and their labels go light.
Scans and screenshots get the full dark treatment, because they are documents wearing an image costume. Scanner dust is removed first, so it does not turn into a field of bright specks.
Images that were already dark are left alone.

Layouts survive too

A CV with a dark sidebar, an invoice with a coloured header band, a slide with a black backdrop — these already have light text on a dark ground, and inverting them would destroy them. The converter notices when light text is drawn on a dark block and leaves that whole region as it was. Highlighter strokes are handled the same way in reverse: the highlight stays bright and the text on it stays dark, exactly as you marked it.

It is still a real PDF

Rather than turning pages into pictures, the converter rewrites the colour instructions inside the file. Text stays selectable and searchable, hyperlinks keep working, bookmarks stay put, page sizes are untouched and the file stays close to its original size. A small number of unusual pages — exotic colour spaces, JPEG 2000 imagery — fall back to an image-based conversion so they still look right, at the cost of text selection on those pages.

Four styles

Midnight — Balanced charcoal. The best all-round choice.
OLED — True black. Saves battery on OLED screens.
Warm — Low blue light. Easier on the eyes late at night.
Slate — Softer contrast for long reading sessions.

Try it on one of your own PDFs — the preview is free.

More on this

Same converter, pages written for a specific job:

By what you want to do

By device or document

Why inverting a PDF looks bad — the colour theory behind all of this, for anyone who wants the detail.