Invert the colours of a PDF
Flip a PDF to a dark background for comfortable night reading while keeping hues intact — or make a full photographic negative.
- Runs in your browser
- Files are never uploaded
- Free, no account
Every page is rendered, inverted and rebuilt, giving you a dark-background copy that is far easier on the eyes at night and uses a fraction of the light on an OLED screen.
A dark copy that stays dark everywhere
Most PDF readers have some kind of night mode, and it always stops at the edge of that reader. Send the file to a colleague, open it on an e-reader, load it on a phone, project it in a dark lecture theatre or print it as a slide handout, and you are back to a full page of white.
Inverting the file itself makes the change permanent and portable. The document is dark in every viewer, on every device, with no setting to find and nothing to re-enable.
Dark mode versus a true negative
These produce very different results and the distinction matters.
| Input colour | Dark mode (lightness flip) | True negative (channel inversion) |
|---|---|---|
| White paper | Black | Black |
| Black text | White | White |
| Red stamp | Red | Cyan |
| Blue heading | Blue | Orange |
| Mid grey | Mid grey | Mid grey |
Dark mode works on each pixel's lightness while leaving hue and saturation where they are:
for a channel value c with the pixel's brightest and darkest channels
max and min, the new value is 255 − max − min + c.
The ordering of the three channels — which is what your eye reads as hue — is preserved
exactly, while the lightest becomes the darkest. A true negative simply computes
255 − c per channel, which flips hue to its complement as a side effect.
Use dark mode for reading. Use the true negative when you actually want a negative: reading a scanned film strip, recovering a photograph of a chalkboard, or inspecting a lithography mask.
Battery and eye comfort, honestly
On an OLED or AMOLED screen — most modern phones, many tablets, some laptops — black pixels are switched off rather than illuminated. A page of text is overwhelmingly background, so an inverted document genuinely cuts panel power, often substantially at high brightness.
On an LCD the backlight stays on regardless and there is no power saving at all. The benefit there is comfort: less light thrown into a dark room, which most people find easier over a long reading session. Neither effect is a health claim, and the evidence on dark text versus light text for reading speed and eye strain in normal daylight actually favours dark-on-light. Invert for night reading, not as a default.
What inversion costs
- The text layer. Recolouring means rendering every page, so the output is images. Nothing is selectable, searchable or screen-reader accessible, and links stop working. Keep the original.
- Photographs. Inverting a page inverts the pictures on it. Dark mode is less alarming than a true negative because hues survive, but a page dominated by photographs is usually better read as it is.
- File size. Rendered pages are frequently larger than a compact vector original. The result panel shows exactly how much changed.
- Printing. Do not. A fully inverted page uses an enormous amount of toner and looks terrible. This is a screen-reading format.
Practical settings
For reading on a phone or tablet, 110 or 150 DPI at 82% quality gives a compact file that still looks sharp on a high-density display. For a large-format technical drawing you intend to zoom into, go to 200 or 300 DPI and accept the size. Use the compare button to hold the original on screen — flicking between the two is the quickest way to judge whether dark mode or a true negative suits the document.
Related
PDF to Grayscale shares the same rendering pipeline and is the tool for cheap mono printing, including a true 1-bit mode. PDF to PNG exports pages as image files if you would rather invert them in an image editor. Compress PDF is the right answer if all you actually want is a smaller file with its text intact.
Questions
What is the difference between dark mode and a true negative?
A true negative inverts every colour channel, so white becomes black and red becomes cyan — correct for reading a scanned film negative, jarring for a document. Dark mode flips lightness while leaving hue and saturation alone: the paper goes black, the text goes white, and a red stamp is still red. For night reading you want dark mode; for a photographic negative you want the true inversion.
Why not just use my reader's night mode?
Because it only applies inside that reader. An inverted file is inverted everywhere — on an e-reader, on a phone, on a projector in a dark lecture theatre, and when printed as a dark slide handout. It also survives being emailed to someone whose reader has no such setting.
Does this save battery?
On an OLED or AMOLED screen, yes, meaningfully — black pixels are switched off rather than lit, and a page of documents is mostly background. On an LCD the backlight stays on regardless, so the benefit is comfort rather than power.
Will the text still be selectable?
No. Recolouring requires rendering each page and rebuilding the document from the resulting images, so the output has no text layer. Keep the original for searching and quoting, and treat the inverted copy as a reading version.
Should I invert a document that contains photographs?
Probably not the whole thing. Inverting a page turns its photographs into negatives too, which usually looks wrong. Dark mode keeps hues so it is less alarming than a true negative, but a page dominated by images is better read as it is.