Grayscale PDF

Turn every page of a colour document grey, at the resolution you choose, without the file leaving your machine.

Runs on your devicePDFWorkingNo account needed

What this tool does

Grayscale PDF opens your document with pdf.js and draws each page onto a canvas at the resolution you pick, over a white background, so anything transparent in the original arrives as white. Every pixel is then reduced to one grey value using the Rec. 709 luminance weights — green carries most of the brightness, red about a fifth of it, blue the small remainder. The grey pages are encoded as JPEGs and assembled into a fresh document by pdf-lib, each one keeping the width and height in points that it had before.

That method is also the whole limitation, and it is worth reading before you convert anything you care about. A browser cannot reach into a PDF's content streams and rewrite the colour operators, so the only conversion available here is to re-render each page and embed the result as a picture. The text becomes part of that picture: it stops being selectable and searchable, and links, bookmarks, form fields, annotations and document metadata are not carried into the new file. Line art is fixed at whatever resolution you rendered it, and recolouring vector content in place — the approach that would preserve all of this — needs a server-side toolchain that this tool does not use.

File size moves in whichever direction the source invites, and it is not always downwards. A colour scan usually shrinks, because one channel of grey detail compresses more tightly than three channels of colour. A text-only report usually grows, sometimes several times over, because crisp glyph instructions are replaced by 200 dpi photographs of themselves. If what you actually want is a mono printout, the greyscale setting in your printer driver costs nothing, changes no file, and leaves the text intact; this tool is for the cases where the document itself has to be grey when it arrives somewhere.

One further consequence of working from brightness is that the primaries are spread very unevenly. A saturated blue falls to about 18 of 255 and reads as almost black, yellow rises to about 237 and reads as almost white, while a saturated red and a saturated green stay far apart at roughly 54 and 182. What does collide is the middle of the range: the mid blue, green and purple that charting libraries reach for by default can finish within a couple of dozen levels of each other and become genuinely hard to tell apart. The contrast control, adjustable from 50 to 200 per cent, multiplies each level's distance from the mid-tone and can pull such lines apart, at the cost of clipping — anything pushed beyond either end lands on pure white or pure black and stays there. All of this happens in this browser tab on your own processor, page by page, with the PDF read from disk into memory rather than sent anywhere.

How to use it

  1. Add the document. Convert one PDF, or queue several — each is processed in turn and comes back with -grayscale added to its name.
  2. Choose the rendering resolution. 150 dpi for reading on screen, 200 dpi as the default, 300 dpi when the result is going to a printer. Each step up means a longer run and a larger file, and a poster-sized page at 300 dpi can ask for more canvas than the browser will allocate, which ends the run with an error instead of a file.
  3. Set the JPEG quality and contrast. Quality runs from 40 to 100 per cent and defaults to 85. Contrast defaults to 100 per cent, which keeps the greys exactly as the luminance measured them.
  4. Inspect a page before you rely on it. Open the result and look at the smallest type and the thinnest rules. If either has softened, run it again at 300 dpi or with the quality raised.

Processing & privacy

Runs on your device. Your file is processed directly in this browser.

Common use cases

Printing where colour pages are billed separately

Copy shops and office printers often count any page containing colour as a colour page. A file with no colour in it cannot be counted that way.

Stripping a tinted letterhead or brand wash

A pale corporate colour behind body text prints as an unpredictable grey. Removing colour beforehand means you see on screen what will come off the press.

Archiving a colour scan of a black-ink document

The scanner captured three channels the paper never used. Flattening to grey keeps the content and drops the rest.

Checking a design for mono legibility

Pale yellow on white, or two brand colours of equal weight, look fine in colour and vanish in grey. Converting a proof shows the problem while it can still be fixed.

Questions

Does the document leave my computer?
No. Grayscale PDF renders, desaturates and rebuilds every page inside this browser tab, using copies of pdf.js and pdf-lib served from this site. The file is read from your disk into memory and is not transmitted, logged or stored.
Is a black and white PDF the same as a greyscale one?
Not strictly. Black and white in the technical sense means every pixel is one or the other, which suits line drawings and ruins photographs. This tool produces greyscale — the full range of levels between black and white — which is what is usually meant by a black and white PDF in everyday use.
Is the text still searchable in the grey copy?
No. Each page is re-rendered as an image, so the text layer does not survive the conversion. Keep the original if you need to search it, or run PDF OCR over the grey copy to put a new text layer behind the pictures — that one is a server tool, so the file is uploaded for the OCR pass.
Why is the greyscale file larger than the colour original?
Because a page of type is cheap to store as instructions and expensive to store as a photograph. A 200 dpi rendering holds millions of pixels where the source held a few thousand references to glyphs. Dropping to 150 dpi or lowering the JPEG quality narrows the gap; nothing closes it while the page is an image.
What happens with a password-protected document?
If a password is needed to open it, the renderer stops and the message names the file. Remove the password with Unlock PDF first, using the password you already hold — that tool runs on the server, so the document goes up to it — then convert the result here. A file encrypted only to restrict printing or copying, with no password on opening, converts normally.
Will a print shop accept the result as a true greyscale file?
Usually, but ask if the job depends on it. The pages are embedded as ordinary JPEGs whose pixels happen to be neutral, not as a single-channel grey image, so a pre-press check that looks at colour space may still report them as RGB even though no colour remains in them.

Related tools

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  • Compress PDF — Reduce PDF file size while preserving the quality that matters.
  • PDF to JPG — Export every page of a PDF as a JPG image.
  • JPG to PDF — Turn one or many JPG photos into a single PDF.
  • Protect PDF — Add a password and set permissions on a PDF.