MammothPDF
Tools

Convert PDF to grayscale

Every colour in the file becomes its grey: the text and vector drawing rewritten operator by operator, the images re-encoded, the gradients and spot colours recomputed, the annotations included. The pages are not rendered to pictures, so text stays sharp and selectable, and the file usually gets a little smaller. For a print job in black, a photocopy-ready handout, or an archive that shouldn't carry colour.

Drop PDF files here

Drag them straight from your desktop

or
  • PDF files only
  • Up to 15 MB each
  • 2 files a run - unlimited with Pro

Frequently asked questions

Does it turn the pages into pictures?

No. The file is rewritten, not rendered: every colour operator in the page content becomes its grey value, images are converted in place, gradients get grey colour functions. Text stays text - sharp at any zoom, selectable, searchable - and bookmarks, links and forms survive.

How is the grey computed?

As the PDF standard recommends: 0.299 × red + 0.587 × green + 0.114 × blue, which is how the eye weighs the three; CMYK goes through the same weights plus the black channel. Dark red and dark blue come out as different greys, as they would on a black-and-white printer.

Does the file get bigger?

Usually a little smaller. JPEG photos are re-encoded at the same size class, and raw images lose two thirds of their bytes as one channel replaces three. A file that carries a JPEG 2000 or 16-bit image keeps it in colour - the tool says so.

Is the PDF uploaded?

Nothing is uploaded: the file is opened and processed inside your browser and never leaves your device. Close the tab and it is gone.

Missing something, or did the result surprise you?